Interleukin-5 and IL-5 receptor in health and diseases
By Kiyoshi TAKATSU*1,*2,†
(Communicated by Tadamitsu KISHIMOTO, M.J.A.)
growth and terminal differentiation of mouse B cells in vitro into antibody-secreting cells,
recombinant IL-5 exerts pleiotropic activities on various target cells including B cells, eosinophils,
and basophils. IL-5 is produced by both hematopoietic and non-hematopoietic cells including T
cells, granulocytes, and natural helper cells. IL-5 exerts its effects for proliferation and
differentiation via receptors that comprise an IL-5-specific , and common O-subunit. IL-5R,
expression in activated B cells is regulated by a complex of transcription factors including E12, E47,
Sp1, c/EBPO, and Oct2. IL-5 signals are transduced through JAK–STAT, Btk, and Ras/Raf-ERK
signaling pathways and lead to maintenance of survival and functions of B cells and eosinophils.
Overexpression of IL-5 in vivo significantly increases eosinophils and B cells in number, while mice
lacking a functional gene for IL-5 or IL-5 receptor display a number of developmental and functional
impairments in B cells and eosinophil lineages. In humans, the biologic effects of IL-5 are best
characterized for eosinophils. The recent expansion in our understanding of eosinophil development
and activation and pathogenesis of eosinophil-dependent inflammatory diseases has led to advance
in therapeutic options. Intravenous administration of humanized anti-IL-5 monoclonal antibody
reduces baseline bronchial mucosal eosinophils in mild asthma; providing important implications for
strategies that inhibit the actions of IL-5 to treat asthma and other allergic diseases.
While interleukin-5 (IL-5) is initially identified by its ability to support the
cytokine, eosinophil, B cells, innate immunity, acquired immunity, asthma
The immune system consists of at least two
categories, innate and acquired immune responses.
Innate immune responses are responsible for the first
line of defense against many microorganisms or tissue
injury. They are mediated by macrophage/dendritic
cells (DC), NK and NKT cells and leukocytes
including eosinophils, neutrophils, and mast cells
that recognize pathogen-associated molecular pat-
terns (PAMPs) through germline-encoded pattern
recognition receptors such as the toll-like receptor
(TLR) or Nod-like receptor (NLR) family.1),2)TLRs,
expressed on a diverse variety of cells, recognize
PAMPs derived from various classes of pathogens.
Activation of TLRs by relevant ligands induces a
conserved host defense program, which includes
production of inflammatory cytokines and interfer-
ons, upregulation of costimulatory molecules, and
induction of antimicrobial defenses. The NLR family
is important for inflammation and tissue damage
that is activated by various crystals, ATP and
amyloid-O.3)Activation of DC by TLR ligands plays
a critical role necessary for maturation and conse-
quent ability to initiate and activate acquired
Department of Immunobiology and Pharmacological
Genetics, Graduate School of Medicine and Pharmaceutical
Sciences, University of Toyama, Toyama, Japan.
Research, Toyama, Japan.
Correspondence should be addressed: K. Takatsu, Depart-
ment of Immunobiology and Pharmacological Genetics, Graduate
School of Medicine and Pharmaceutical Science, University of
Toyama, Toyama 930-0194, Japan (e-mail: email@example.com-
Abbreviations: AID: activation-induced cytidine deami-
nase; ASC: antibody-secreting cells; BCGFII: B cell growth factor
II; CSR: class switch recombination; DC: dendritic cells; EDF:
eosinophil differentiation factor; IL: interleukin; PAMPs: patho-
gen-associated molecular patterns; SHM: somatic hypermutation;
STAT: signal transducer and activator of transcription; Tbc:
Mycobacterium tuberculosis; TH: CD4DT helper cells; TLR: Toll-
like receptor; TRF: T cell-replacing factor.
Proc. Jpn. Acad., Ser. B 87 (2011)No. 8]463
©2011 The Japan Academy
Acquired immune responses are involved in
the late phase of infection and the generation of
immunological memory that is mediated by a series
of interactions among T, B, and antigen-presenting
cells.4)Activation of T cells by antigenic peptide
through specific T-cell receptor (TCR) induces the
release of cytokines and chemokines that augments
the phagocytosis and triggers B and T cells leading
to regulation of both humoral and cell-mediated
Mature B cells expressing surface IgM as B-cell
receptor (BCR) are destined to differentiate into
antibody-secreting cells (ASC) after appropriate
stimulation with antigen and T helper (TH) cells.
The B cells are subdivided into B-1 and conventional
B (B-2) cells that regulate the innate and acquired
immune responses, respectively. B-1 cells can be
distinguished from B-2 cells by their expression of
surface markers and have numerous noteworthy
characteristics, such as their self-replenishing ability,
particular tissue distribution (abundant in the
peritoneal and pleural cavity), VH gene usage of
IgM, and production of autoantibodies.5)B-1 cells
form a minor population (less than 5%) of the total
splenic B cell pool and are absent from lymph nodes.
Coupled to the observation that autoimmune mice
have a higher number of B-1 cells as compared to
normal mice, B-1 cells may play important roles in
the development of autoimmune diseases.6)
Activated B-2 cells respond to protein antigens
and interact with THcells, which express a TCR,
resulting in proliferation and differentiation into
ASC. THcells recognize the peptide–MHC complex
presented on the B cells and transiently express CD40
ligand (CD40L) on their surface, which is required for
interaction with B cells through CD40 and LMP1,
and produce cytokines.7)
stimulation of B-2 cells induces genetic events in
their IgH gene loci that are essential for the generation
of functional diversity in the humoral immune
response and for efficient antigen elimination. Class
switch recombination (CSR) replaces the heavy chain
constant region (CH) from C7 to other CHregions to
diversify the effector function of the Ig.8),9)The
process of CSR is highly regulated by cytokines, B
cell activators or both. The efficiency of antigen
elimination is also augmented by affinity maturation
of antibodies, which is accomplished by excessive
point mutations in the V-region gene by somatic
hypermutation (SHM). Activation-induced cytidine
deaminase (AID) is the essential and sole B cell-
specific factor required for CSR and SHM.10),11)
Antigen and TH cell
Transcriptional regulators, including Blimp-1, Bach
2, Bcl6, IRF4, Xbp-1 and Pax5 organize the transition
from the mature switched B cell genetic programs to
high level antibody synthesis and secretion.12),13)
Allergic diseases including asthma and atopic
diseases are characterized by inflammation with
pronounced infiltration of T cells and granulocytes
such as mast cells, eosinophils, and neutrophils.14),15)
IgE-mediated degranulation of mast cells contributes
to inflammatory infiltrates and acute bronchocon-
striction in the early phase of allergic inflammation,
whereas recruitment of CD4DT cells and eosinophils
is a central feature of the late-phase response.
Pulmonary allergen exposure results in both in-
creased output of eosinophils from hemopoietic
tissues and increased migration to the lung. Eosino-
phils are produced in bone marrow and proliferate
under a wide variety of conditions, including allergic
diseases, helminthes infections, drug hypersensitivity,
and neoplastic disorders. T-cell-derived cytokines
and eosinophils are thought to play critical roles
in the induction of airways hyperreactivity and the
development of lesions that underpin chronic airway
In the 1980s, numerous attempts were made
to disclose the molecular nature of T-cell derived
cytokines17)–20)such as T cell-replacing factor (TRF)
that are involved in activated B cell differentiation
in the absence of T cells. We have analyzed the
roles of a T-cell-derived cytokine, at first calling it
“Enhancing factor on anti-hapten antibody response”
and later “TRF” on anti-hapten IgG response of
T-cell-depleted mouse B cells.21),22)We developed
monoclonal antibody (mAb) against TRF23)and
isolated cDNA encoding the TRF active molecule.24)
As recombinant TRF exerts pleiotropic activities on
various target cells beside B cells, we proposed calling
TRF as “interleukin 5 (IL-5)”.24),25)Recombinant
IL-5 activates mouse B cells and eosinophils for
their proliferation and differentiation. In humans,
the biological effects of IL-5 are best characterized
This review summarizes the advances of IL-5
and IL-5R researches in studying the structure,
physiologic functions, and unique mode of receptor-
mediated signaling. The pathophysiology of aberrant
expression of IL-5 and its receptor regarding allergic
inflammation is also discussed.
2. Interleukin 5, IL-5
(1) Historical background.
induces terminal differentiation of B cells to Ig-
A factor that
secreting cells is originally designated as TRF.18)
Dutton et al.17)as well as Schimpl and Wecker18)
demonstrated that supernatants of mixed lymphocyte
cultures or concanavalin A-stimulated T cells contain
TRF activity. These TRF preparations exert remark-
able effects in a number of different assays of T- and
B-cell activity. TRF activity is mainly screened with
the use of dinitrophenyl (DNP)-primed mouse B cells
by its ability to support the anti-DNP IgG-ASC18)
response. Biochemical characterization of TRF takes
a long time partly because purification of TRF is
difficult and its assay system is complicated.
Howard et al.29)described the first B-cell growth
factor (BCGF, later referred to as BCGFI) distinct
from IL-2 that had the ability to support B-cell
proliferation. This BCGF synergizes with anti-IgM
antibody for inducing DNA synthesis of resting B
cells. Then Swain and Dutton30)reported the second
T-cell-derived BCGF (BCGFII) active on murine B
cells and distinct from BCGFI, suggesting the
existence of at least two distinct factors affecting B
cell proliferation. They found that TRF-containing
supernatants also showed BCGFII activity for
in vivo growing murine chronic B-cell leukemia
(BCL1) and dextran-sulfate stimulated B cells.
We found TRF activity in supernatants of the
lymph node cell culture of Mycobacterium tuber-
culosis (Tbc)-primed mice after stimulation with the
extracts from Mycobacterium tuberculosis, which
are so called purified protein derivatives (PPD). We
monitored TRF activity by its ability to induce anti-
DNP IgG-ASC from T-cell-depleted DNP-primed B
cells in an adoptive cell transfer system.21)We then
established an in vitro culture system to assess the
TRF activity and examined the TRF-producing T
cell subset.22)We showed that TRF-producing TH
cells were a different subset from Tbc-primed TH
cells for cognate interaction with DNP-primed B cells
through DNP-PPD22),31)(Fig. 1). We also found a
strain of mice, DBA/2Ha whose DNP-primed B cells
are low-responders to TRF preparations, while they
are good responders with Tbc-primed TH cells for
cognate interaction through DNP-PPD,32)–34)sug-
gesting the existence of two different subsets in
activated B cells.
We developed a TRF-producing T cell hybrid-
oma and established a reproducible TRF assay
system using BCL1 cells. Cultured supernatants of
the hybridoma showed TRF activity on BCL1 cells
and induced their differentiation into IgM-ASC.35)–37)
HPLC-purified TRF-active molecule exerts BCGFII
activity on BCL1 cells (Fig. 2A). By using the
HPLC-purified TRF as immunogen, we generated
mAbs that could neutralize TRF activity.23)The
anti-TRF mAb does not neutralize IL-1, IL-2, IL-3,
IL-4 or IFN-. activities. Affinity-purified TRF has a
molecular mass of 50 to 60kDa under non-reducing
conditions and migrates to a smaller mass (25 to
30kDa) under reducing conditions (Fig. 2B). The
reduced and alkylated TRF does not show any
Fig. 1. Schematic illustrations of two different modes of T and B cell interaction for antibody production. APC, antigen-presenting cells.
Details are described in the text.
IL-5 in the immune system and inflammationNo. 8]465
activities, indicating that T-cell-derived TRF con-
sists of homodimers and its dimer formation is
essential for exerting biological activities.
The molecular cloning of cDNA encoding mouse
TRF and functional assessment of recombinant TRF
have convincingly demonstrated that a single mole-
cule is responsible for both TRF and BCGFII
activities.24)Furthermore, recombinant TRF exerts
pleiotropic activities on activated T cells and
eosinophils besides B cells.38)–41)We therefore pro-
posed calling TRF “IL-5”. IL-5 is a synonym of
cytokine called TRF, BCGFII, IgA-enhancing factor,
IL-2R,-inducing factor, killer helper factor, EDF,
and eosinophil colony stimulating factor.
(2) Cloning of the gene and its organization.
Mouse IL-5 cDNA was isolated by using the expres-
sion vector system containing the SP6 promoter. The
cDNA libraries were constructed from poly(A)DRNA
of allo-reactive T-cell clone, 2.19.24)Pools of recombi-
nant plasmid DNA from the SP6 library of 2.19
mRNA were transcribed in vitro into mRNA using
SP6 RNA polymerase. mRNA synthesized in vitro
was microinjected into Xenopus oocytes and oocytes’
culture supernatants were assayed for TRF activ-
ities.42)Pools that scored positive in the biological
assays were further divided into smaller pools, which
were synthesized in the same manner until single
cDNA clones capable of directing the synthesis of
biologically active TRF preparations were obtained.
The isolated IL-5 cDNA clone was subjected to
nucleotide sequencing analyses. The mouse (m) IL-5
cDNA, thus obtained, codes for a polypeptide chain
of 133 residues that contains the N-terminal signal
sequence of 20 residues and the secreted core
polypeptide with a molecular mass of 12.3kDa.24)
Three putative N-glycosylation sites as well as three
Fig. 2.Structure of IL-5. (A) Hydrophobisity of B151-TRF/IL-5. B151-TRF samples from gel permeation column chromatography are
analyzed with HPLC.23)TRF and BCGFII activity of each fraction are determined. (B) SDS-PAGE analysis of affinity purified B151-
TRF/IL-5 (left panel) and TRF activity on BCL1 cells. TRF activity is diminished by reduction with 2-mercaptoethanol and
alkylation with iodoacetamide.23)(C) Alignment of the primary amino acid sequences for recombinant, mouse IL-5.24)(D) Schematic
illustration of tertiary structure of hIL-5 in comparison to hGM-CSF and human growth factor (hGH). Boxes and arrows indicate ,
helices and O-strands.61)
[Vol. 87, 466
cysteine residues are present in the polypeptide
sequence (Table 1 and Fig. 2C). Using the mIL-5
cDNA clone as a probe, human (h) IL-5 cDNA was
isolated from a cDNA library constructed with
poly(A)DmRNA extracted from ATL-2 cells.43)The
isolated hIL-5 cDNA clone encodes a polypeptide
consisting of 134 residues, containing an N-terminal
signal peptide of 19 residues. The nucleotide and
amino acid sequence homologies of the coding regions
of hIL-5 and mIL-5 are 77% and 70%, respectively.
The cDNA clone coding for hEDF is independently
isolated by other groups and entire amino acid
sequences are identical to that of hIL-5.44)
The chromosomal genes for mouse and human
IL-5 are isolated using IL-5 cDNAs as probes.
Nucleotide sequence analyses of the IL-5 genes as
well as flanking regions show that IL-5 genes consist
of four exons and three introns.42)Conserved TATA-
like motif and the lymphokine element (CLE0, CLE1,
CLE2) are found at about 30 and 70 base pairs,
respectively, upstream of the transcription initiation
sites. The CLE0 element has been shown to be crucial
for IL-5 expression.45)As the exon–intron organiza-
tion and the location of the cysteine codons of the
IL-5 genes resemble those of the GM-CSF, IL-2,
and IL-4, the IL-5 gene might be evolutionarily
related to the genes for IL-2, IL-4, and GM-CSF
genes. The genes encoding IL-3, IL-4, IL-5, IL-13, and
GM-CSF are located in a cluster on mouse chromo-
some 11 and in the syntenic region of human
During TH2 cell differentiation from naïve T
cells, changes in the chromatin structure of the TH2
cytokines (IL-4/IL-5/IL-13) gene loci are induced. It
is frequently asserted that the expression of IL-4 and
IL-5 is coordinately controlled, implying a common
mechanism of gene expression. GATA-3 antisense
RNA inhibits IL-5 but not IL-4 promoter activa-
tion.47)Furthermore, ectopic expression of GATA-3
is sufficient to drive IL-5, but not IL-4 gene
expression. Hyperacetylation of histone H3 on
nucleosomes observed in TH2 cells is associated with
IL-5 gene expression that is STAT6- and GATA-3-
dependent.48)Interestingly, the loss of GATA-3
expression results in decreased TH2 cytokine produc-
tion and reduction of histone hyperacetylation at the
IL-5 gene locus but not so at the IL-13/IL-4 gene
loci.48)Collectively, GATA-3 is sufficient for optimal
expression of the IL-5 gene but not the IL-4 gene.
(3) Protein in structure. A single polypeptide
with a molecular mass of 14kDa is secreted when
mIL-5 mRNA is transiently translated in rabbit
reticulocyte lysates.49)Mouse (m) and human (h) IL-
5 are disulfide-linked homodimer with a molecular
mass of 50 to 60kDa.23),42)The large variation in the
molecular weight of IL-5 is predominantly as a result
of the heterogeneous addition of carbohydrate in
Table 1.Physical properties of IL-5
1. Gene locus
2. Gene structure
3. Primary structures
3 N-glycosylation sites
4 alpha helices
2 beta strands
2 helical bundle motifs
2-fold axis of symmetry
Natural helper cells
2 N-glycosylation sites
4 alpha helices
2 beta strands
2 helical bundle motifs
2-fold axis of symmetry
NK and NKT cells
Reed Sternberg cells
4. Secondary structure
5. Tertiary structure
6. Molecular weight
7. Producing cells
IL-5 in the immune system and inflammation No. 8]467
The crystal structure analysis of hIL-5 has
revealed that IL-5 is a unique member of the short-
chain helical-bundle subfamily of cytokines whose
canonical motif contains four helices (A–D) arranged
in an up-up-down-down topology (Fig. 2D). Other
subfamily members fold unimolecularly into a single
helical bundle, while IL-5 forms a pair of helical
bundles of two identical monomers that contribute a
D helix to the other’s A–C helices.51)The tertiary
structure of hIL-5 can explain why IL-5 is required
for dimerization in expressing its biological activities.
The lack of bioactivity by an IL-5 monomer is
predicted to be due to a short loop between helices C
and D that physically prevents unimolecular folding
of helix D into a functionally obligate structural
motif. By engineering an insertional mutant of IL-5
that is expressed as a monomer with biological
activity similar to that of native IL-5, Dickason
and Huston demonstrate that all of the structural
features necessary for IL-5 to function are contained
within a single helical bundle.52)
(4) IL-5-producing cells.
producing T-cell hybridoma constitutively expresses
1.7-kb IL-5 mRNA whose expression is augmented by
stimulation with PMA plus calcium ionophore.49)
The T cells from Tbc-primed mice and nematode-
infected mice express the IL-5 mRNA and produce
IL-5 upon stimulation with PPD and nematode-
antigens, respectively. IL-1 is required for efficient
IL-5 production by TH cells. The mIL-5 mRNA
expression is undetectable in PMA plus calcium
ionophore-stimulated spleen cells from naïve mice,
while remarkable mIL-2 mRNA expression is de-
tected.25),49)We proposed that IL-5-producing TH
cells could comprise a different subset from that of
IL-2-producing TH cells. Mosmann and Coffman
clearly demonstrate that IL-5, IL-4, and IL-10 are
produced by TH2 cells that are distinct T-cell subsets
from TH1 cells, which produce IL-2, IFN-., and TNF-
O.53)Our results are good in good agreement with
The significant IL-5 mRNA expression is detect-
able in the lungs, spleen, and small intestine of wild
type, RAG-2!/!and TCRO!/!/!/!mice.54)Further-
more, IL-5 mRNA expression is detected in c-Kit!IL-
5R,!/!cells in the lungs and small intestine of RAG-
2!/!mice. CD4!c-Kit!CD3C!IL-2R,Dcells in the
mouse Peyer’s patch (designated PP CD3!IL-2RD
cells) are also reported to produce high levels of IL-5
upon stimulation with IL-2 or PMA plus A23187.55)
The exact origin of PP CD3!IL-2RDcells has not
been clarified. Recently, Moro et al. identified IL-5-
In mice, IL-5-
producing c-KitDnatural helper cells in lymphoid
clusters in adipose tissues in the peritoneal cavity.56)
The natural helper cells, a new type of innate
lymphocyte subset of Lin!c-KitDSca-1DIL-7RDIL-
33RDcells, proliferate in response to IL-2 resulting
in the production of large amounts of IL-5 together
with IL-6 and IL-13. They also produce large
amounts of IL-5 upon stimulation with IL-33 or
To analyze the localization of IL-5-producing
cells, we generated IL-5/Venus knock-in mice and
found that the expression of IL-5 along with Venus
was detected in IL-5D/VenusT cells cultured under
TH2-skewing conditions. No IL-5 but strong Venus
expression was detected in IL-5Venus/VenusCD4DT
cells or in TH1-skewed T cells. We also identified
innate IL-5-producing VenusDLin!c-KitDSca-1D
T1/ST2Dcells (referred to as innate IL-5-producing
cells) in the small and large intestines, peritoneal
cavity, and the lung in non-immunized IL-5D/Venus
naïve mice. The innate IL-5-producing cells possess
several similarities with natural helper cells, but show
different tissue localization (Ikutani and Takatsu,
unpublished data). Innate IL-5-producing cells in the
intestine proliferate in response to IL-25 and IL-33
resulting to enhance mucosal IgA production. A
higher proportion of innate IL-5-producing cells is
observed in the lung of IL-5D/VenusC57BL/6 mice
than IL-5-producing T cells, while IL-5-producing TH
cells reside mainly in the peritoneal cavity in IL-
5D/VenusBALB/c mice.57)As BALB/c and C57BL/6
mice differ in the nature of the pathophysiology of
allergic airway diseases and also exhibit variations in
underlying mechanisms,58),59)different localization of
innate IL-5-producing cells in the lung in C57BL/6
than BALB/c mice may have relevance with strain
difference for asthma pathogenesis.
The hIL-5 mRNA is detected in bronchoalveolar
lavage T cells of mild atopic asthma subjects. It is
also detected in HTLV-1-infected T cells, trans-
formed human B cells by the Epstein–Barr virus,
and Reed–Sternberg cells of Hodgkin’s disease with
eosinophilia. The Reed–Sternberg cells are malignant
cells that are essential to the diagnosis of Hodgkin
lymphoma. In situ hybridization studies on cyto-
preparations of Hodgkin’s disease with eosinophilia
reveal striking localization of the hIL-5 mRNA to the
cytoplasm of Reed–Sternberg cells and variants,60)
while it is undetectable in a case of Hodgkin’s disease
without eosinophilia. This observation indicates the
IL-5 mRNA may explain the eosinophilia associated
with Hodgkin’s disease.
Eosinophils infiltrating into the mucosa of
patients with active coeliac disease express the
hIL-5 mRNA, suggesting that eosinophils have the
potential to synthesize IL-5. Mast cells, ./T cells, NK
and NKT cells, and non-hematopoietic cells including
epithelial cells can also produce IL-5.61)
3. IL-5 receptor
IL-5 acts on target cells by binding to its specific
IL-5 receptor (IL-5R). In mice, IL-5 responsive B cells
and eosinophils express small numbers (approxi-
mately 50) of high-affinity IL-5R (Kd of 10–
150pM) and large numbers (around 1,000) of low-
affinity IL-5R (Kd of 2–10nM)62),63)(Fig. 3A). Bio-
logical responsiveness to mIL-5 depends on interac-
tion with the high affinity IL-5R. Chemical cross-
linking studies of mIL-5R with IL-5 reveal that the
high affinity mIL-5R consists of two distinct sub-
units, , and O (Fig. 3B).63)IL-5 specifically binds to
the IL-5R, subunit. We developed anti-IL-5R,
mAb, H7 that could recognize 60kDa proteins on
IL-5-responsive cells and specifically inhibit IL-5-
dependent cell proliferation.64),65)Rolink and his
R52.120, which partially inhibited IL-5-induced
cell proliferation and recognized 130kDa proteins.66)
Interestingly, addition of H7 and R51.120 mAbs to
the cell culture completely inhibited IL-5-induced
proliferation (Fig. 3C).67)As anti-IL-3R mAb, Aic2B
showed similar inhibitory activity to that of R52.120,
we speculated that H7 and R52.120 could recognize
IL-5R, and IL-5RO subunit, respectively (Fig. 3D).
(1) IL-5R , subunit.
cDNA encoding mIL-5R, on IL-5-dependent early B
cell line is carried out by using anti-mIL-5R, mAb.68)
Nucleotide sequence analysis of the cDNA reveals
that the mIL-5R, is a type-I transmembrane protein
of 415 amino acids including an amino-terminal
Expression cloning of
Fig. 3.IL-5 binding and chemical crosslinking of IL-5 binding protein. (A) IL-5 binding assay shows existence of the low- and high
affinity IL-5 receptor on IL-5 responsive B cell lines.63)(B) Chemical crosslinking of IL-5 binding protein from B cell lines. Crosslinking
studies using3SS-labeled IL-5 detected 160kDa and 92.5kDa band under high-affinity conditions, while only 92.5kDa bands were
detected under low-affinity conditions.63)(C) Inhibitory effects of anti-IL-5R mAb (H7 and R52) and anti-IL-3R mAb (Aic-2B) on
IL-5-induced DNA synthesis of IL-5-dependent Y16 cells.67)(D) Schematic illustration of IL-5 receptor complex. Details are described
in the text.
IL-5 in the immune system and inflammationNo. 8]469
signal peptide, a glycosylated extracellular domain, a
single transmembrane segment, and a cytoplasmic
tail (Fig. 4A). The sequence of amino-terminal 17
amino acids of affinity purified mIL-5R, from BCL1
is identical to that deduced from the nucleotide
sequence of the mIL-5R, cDNA, confirming the
inferred amino-terminus of the mature mIL-5R,
protein.41),68)The extracellular domain of the mIL-
5R, contains two motifs that are conserved in a set
of type I cytokine receptor family;69)a particular
spacing of four cysteine residues and the tryptophan-
serine-X-tryptophan-serine (WSXWS) motifs located
close to the transmembrane domain. In addition, the
extracellular region comprises three tandemly re-
peated sets of a fibronectin type III domain, while the
cytoplasmic domain does not contain the consensus
sequences for a tyrosine kinase domain. Interestingly,
the cytoplasmic domain has a motif rich in proline,
PPXP motif following the transmembrane domain
that is well conserved among IL-5R,, IL-3R,, GM-
CSFR,, prolactin and growth hormone receptor.68)
The carboxy-terminal region of IL-5R, is essential
for regulating IL-5-induced IgH class switch recombi-
cDNAs of the hIL-5R, subunit have been
isolated from human eosinophils and a cell line,
HL60.71),72)The entire nucleotide sequence of hIL-
5R, cDNAs shows considerable similarity to the
coding sequence of the mIL-5R,, and the amino acid
sequence of the hIL-5R, has about 70% homology
with the mIL-5R, and retains features common to
the cytokine receptor superfamily. The cytoplasmic
regions rich in proline residues following the trans-
membrane domain are well conserved.
COS7 transfectants expressing the mIL-5R,
cDNA bind IL-5 with low-affinity, but they do not
respond to IL-568)(Fig. 4B). cDNAs coding for
soluble forms of both mIL-5R, and hIL-5R, have
been isolated.68),71),73)Human eosinophils express,
through differential splicing, two forms of soluble
Fig. 4. Structure of IL-5 receptor. (A) Comparison of molecular constitution of mIL-5R, and hIL-5R,. Conserved four cysteine residues,
WSXWS motif in the extracellular regions and proline-rich residues in the cytoplasmic regions are shown in the figure. (B) Scatchard
plot analysis of35S-labeled IL-5 binding to the recombinant IL-5R, transfectants in COS7 cells.68)(C) IL-5-induced proliferation
of FDC-P1 transfectants expressing recombinant mIL-5,.68)(D) Schematic illustration of molecular components for the IL-5R,
GM-CSFR and IL-5R complex. The mOc and hOc are AIC2B and KH197 protein, respectively.
[Vol. 87, 470
forms of hIL-5R, (s-hIL-5R,) in addition to the
membrane-bound receptor isoform from the same
hIL-5R, locus.73)s-hIL-5R, arises from splicing to a
soluble-specific exon, which precedes the exon encod-
ing the transmembrane domain. In the case of mice,
no evidence for a “soluble” exon has been obtained,
indicating that a different splice pattern is used
for the generation of s-IL-5R, in humans and mice.
It is unclear whether that represents an interspecies
variation or a cell-type-dependent difference. The
recombinant s-hIL-5R, binds hIL-5 with high
affinity and inhibits the hIL-5 activities; however, it
has not been detected in serum or in supernatants of
The mIL-5R, genomic gene is divided into
eleven exons and ten introns and spans more than
35-kb. The gene organization shows a pattern of
considerable structural homology with genomic genes
coding for other cytokine genomic genes such as IL-
2RO, IL-3R, IL-4R, IL-7R, and EpoR. Chromosomal
localization of the mIL-5R, and hIL-5R, genes is
mapped on the distal half of mouse chromosome 6
and human chromosome 3 (3p24–3p26), respectively.
(2) IL-5R O subunit.
mIL-5R, in IL-3-dependent FDC-P1 cells enabled
them to reconstitute high-affinity mIL-5R and
(Fig. 4C), indicating that IL-3-dependent FDC-P1
cells constitutively express the IL-5RO subunit. Anti-
IL-3R mAb was shown to recognize both mIL-3R
(AIC2A) and a homologue protein of mIL-3R
(AIC2B).74)Transfection of Aic2B cDNAs into
mIL-5R,-expressing L cells could induce the high-
affinity IL-5R expression.75)Furthermore, enforced
expression of mIL-5R, and AIC2B in CTLL enabled
them to proliferate in response to IL-5. We conclude
that AIC2B is the mIL-5RO subunit that plays an
indispensable role for the IL-5 signal transduction.
AIC2B does not bind IL-5 in the absence of mIL-
The IL-5RO has a relatively long cytoplasmic
portion and contains motifs conserved among cyto-
kine receptor families. It does not bind any cytokines,
but it contributes to the signaling molecule for mIL-
5, mGM-CSFR and mIL-3R. Thus it is called the
common O subunit (Oc).74)Receptors for IL-5, IL-3,
and GM-CSF are composed of a ligand-specific ,
subunit and a shared Oc as a signal-transducing
subunit (Fig. 4D). Cytoplasmic domains of both IL-
5R, and Oc are indispensable for IL-5 signal trans-
duction. In particular, the membrane proximal motif
rich in proline in the cytoplasmic regions of the IL-
Enforced expression of
5R, and Oc are essential for the signal trans-
duction.76)–78)In humans, KH97, a homologue of
mouse AIC2 could reconstitute high affinity hIL-5R
with hIL-5R,72),79)and transduce IL-5 signals. As
KH97 has been shown to be the O subunit of hGM-
CSFR and hIL-3R,74)KH97 is the hOc and common
signal transducing molecule for hIL-5, hIL-3, and
hGM-CSF. The X-ray structure of the hOc is an
intertwined homodimer in which each chain contains
four domains with approximate fibronectin type-III
topology.80)By fluorescence resonance energy trans-
fer imaging, Oc subunit is demonstrated to exist as
preformed homo-oligomers and the IL-5 stimulation
induces Oc assembly in the presence of IL-5R,.81)
Martinez-Moczygemba and his colleagues dem-
onstrated that following cytokine ligation, Oc signal-
ing is terminated partially by ubiquitination and
proteasome degradation of its cytoplasmic domain,
resulting in the generation of truncated Oc products,
The truncated IL-5R complex (IL-5R, and OIP) is
degraded in the lysosome.
progenitors for B cells and eosinophils.
expression is readily detectable on mouse B-1 cells
and eosinophils.65),83)B-1 cells in the mouse perito-
neum respond to IL-5 resulting in survival and
differentiation to ASC.54),83)IL-5 transgenic mice
show marked increase in proportion and numbers of
B-1 cells with concomitant hypergammaglobulinemia
and autoantibody production.84)They also show
increase in the number of eosinophils in the
peripheral blood (Fig. 5A), and eosinophil infiltra-
tion in various tissues (Fig. 5B and 5C). Passive
administration of anti-IL-5 or anti-IL-5R, mAb into
IL-5 transgenic mice decreases the elevated levels
of B-1 cells and eosinophil numbers in peripheral
blood to normal levels (Fig. 5C).83)IL-5R, deficiency
causes decrease in numbers of B-1 cells and eosino-
phils in the peritoneal cavity up to one-third of wild-
type littermates (Fig. 6A).85)In IL-5R,!/!mice,
serum levels of IgM and IgG3 are decreased
(Fig. 6B). The frequency of IgA-ASC in mucosal
effector sites such as intestinal lamina propria in IL-
5R,!/!mice is reduced. IgA-committed sIgADB-1
cells, but not sIgADB-2 cells in the inductive site such
as Peyer’s patches are also decreased (Fig. 6C),86)
indicating the importance of the IL-5/IL-5R system
for the development of sIgADB-1 cells in mucosal
tissues. Hyperreactivity in the airways of mice that
were immunized and challenged with ovalbumin were
ameliorated in IL-5R,!/!mice (Fig. 6D). These
IL-5 in the immune system and inflammation No. 8] 471
results imply the involvement of IL-5 in the early
development of B-1 cells and eosinophils.
A key question is when and how IL-5R,
expression is triggered in B-1 cell progenitors. IL-
5R,Dcells are found in the lineage marker negative
(Lin!) fraction in fetal bone marrow, but not in
CD19DB220!B-1 progenitor cells87)(Fig. 7). There
are IL-5R,Dcells in the fetal liver that do not
differentiate into B-1 cells in vivo, while IL-5R,!
CD19DB220!fetal liver cells differentiate into B-1
cells. CD19DB220!B-1 progenitor cells in the fetal
liver may acquire inducing signals for IL-5R expres-
sion during migration from the fetal liver to and
maturation in the bone marrow microenvironment.
IL-5 is important for proliferation and survival of
mature B-1 cells.
Most mouse resting B-2 cells constitutively
express Oc and less than 5% of them express IL-
5R,. Once B cells are activated by TH cells and
antigen through BCR and CD40, they express IL-
5R, and become responsive to IL-5 resulting in
integration into the plasma cell differentiation pro-
gram. Corcoran and colleagues reported that Oct-2
contributes to, but does not entirely control IL-5R,
levels.88)Oct2 binds directly to the promoter of the
IL-5R, gene to activate its transcription specifically
in mouse B cells and enhances the ability of the B
cells to differentiate into ASC under T cell-dependent
conditions, through direct genetic regulation of the
gene encoding IL-5R,. The CD38 ligation of splenic
B cells also induces increase in the proportion of IL-
5R,DB cells. In our analysis, the region between bp
!250 and !111 from proximal to the transcriptional
start site is involved in the regulation of IL-5R,
expression in CD38-stimulated mouse B cells. A
complex of transcription factors including E12, E47,
Sp1, c/EBPO, and Oct2 together with unidentified
protein coordinately bind to the promoter of the
mIL-5R, gene and regulate the IL-5R, expres-
Eosinophilic progenitors and mature eosinophils
in mice and humans constitutively express IL-5R,.
The IL-5R, expression in the bone marrow cells is
one of the most critical issues in the eosinophil lineage
commitment.91)The RFX family of DNA binding
proteins binds to the cis element of IL-5R, pro-
moter.92),93)Although expression of RFX1, RFX2,
and RFX3 homodimers and heterodimers is ubiqui-
Fig. 5.Functional characteristics of IL-5 transgenic mouse. (A) Construct of IL-5 transgene and biological properties of the transgenic
mouse.84)(B). Eosinophil infiltration in skeletal muscle. (C) Effect of anti-IL-5 and anti-IL-5R, mAbs on IL-5-induced eosinophilia.
One milligram of anti-IL-5 (NC17) mAb or anti-IL-5R, mAb (H7 and T21) was injected into IL-5 transgenic mouse on Day 0.83)
[Vol. 87, 472
tous, they contribute to the activity and lineage
specificity of the IL-5R, promoter in cooperation
with other factors.93)As for down-regulation of IL-
5R,, all-trans retinoic acid suppresses eosinophilo-
poiesis by down-regulating membrane-bound IL-5R,
and up-regulating s-IL-5R,.
The IL-5R,Dcells in the fetal liver are able to
differentiate into eosinophils in vitro culture under
the influence of cytokine cocktails.91)In the normal
bone marrow, Lin!Sca-1!CD34Dfraction containing
a small number of cells expressing IL-5R, and a low
level of c-Kit,91)which are blastic cells with scattered
eosinophilic granules, respond in vitro to IL-5 or
SCF, IL-3, IL-9, GM-CSF, Epo, and Tpo, leading
to differentiation exclusively into eosinophils. They
are eosinophil progenitor cells (EoPs). In the bone
marrow of mice infected with Trichinella spiralis,
expand in number, while numbers of granulocyte/
monocyte progenitors and common myeloid pro-
5R,DCD34Dc-KitloEoPs may be involved in the
physiological eosinophil development.
are notaffected.Thus, Lin!Sca-1!IL-
4. IL-5R-mediated signaling
IL-5 stimulation induces rapid tyrosine phos-
phorylation of cellular proteins including the Oc,
SH2/SH3-containing proteins such as Vav and Shc,
Btk and Btk-associated molecules, JAK1/JAK2
and STAT1/STAT5, PI3K, and MAP kinases that
activate downstream signaling molecules76)–78),94)–101)
(Fig. 9). Activation of tyrosine kinases and signal
transducer and activator of transcription (STAT)
protein plays an indispensable role in the IL-5
signaling. Regarding the negative regulation of IL-5
signaling, STAT5-induced cytokine inducible SH2
protein (CIS) and JAK2-binding SH2-containing
protein (JAB, also called SOCS1) play a role in
eosinophils, which are one of the feedback loops of IL-
5 signaling.96)IL-5 also activates NF-5B in activated
Fig. 6.Functional features of IL-5R,!/!mouse. (A) Expression of IL-5R, on B cells from the peritoneal cavity of wild-type (D/D) and
IL-5R, deficient (!/!) mouse.85)(B) Serum levels IgM, IgG3, IgG1, and IgA. Each spot represents an individual mouse. ( ) denotes
wild-type and ( ) denotes the IL-5R,!/!mouse.85)(C) Confocal immunofluorescence microscopy analysis of IgA-producing cells in
the intestinal tract of IL-5R,!/!mouse.86)(D) Histological analysis of lung sections from wild-type (WT) and IL-5R,!/!mice 24hr
after OVA challenge. Mice were immunized with OVA in alum 2wks before the OVA challenge.118)
IL-5 in the immune system and inflammation No. 8]473
B-2 cells and eosinophils, which is dependent on
TNFR-associated factor 6 (TRAF6).100)IL-5 enhan-
ces the gene expression of c-Myc, c-Fos, c-Jun, Cis,
Cish1/Jab, and pim-1 in B cells.77),96)The JAK/c-
Myc pathway is indispensable for IL-5-induced cell
proliferation and anti-apoptosis, and IL-5-induced
up-regulation of c-Myc is dependent upon JAK1 and
(1) JAK and STAT pathway. Binding of IL-5
to IL-5R on mouse B cells and eosinophils from
mice and humans activates JAK1/2 and STAT1/
5.76)–78),98),99)Analyses of JAK kinase activation
domain in the cytoplasmic domain in human
eosinophils revealed that JAK2 was constitutively
associated with hIL-5R, regardless of IL-5 stimula-
tion.76)JAK1 was constitutively associated with Oc
and was able to associate with hIL-5R, only after
cells were stimulated with IL-5. As with the IL-5R
system, JAK2 and JAK1 are reported to constitu-
tively associate with the hIL-3R, and Oc, respec-
tively in the hIL-3R system.98)The region of hIL-5R,
necessary for JAK2 binding is located in amino acid
residues 346–387 including proline-rich sequences
of the cytoplasmic domain (Fig. 9B). These results
indicate that the downstream region of motif rich in
proline (PPXP motif) in hIL-5R, is indispensable for
significant JAK2 binding and signal transduction.
The JAK1 N-terminus binds to conserved regions of
proline-rich motif (Box 1 and Box 2) of Oc, but signal
activation requires JAK1 C-terminus.98)
By using COS7 transfectants expressing intact
Oc and a kinase-negative form of JAK1 and JAK2
(DN-JAK1 and DN-JAK2, respectively), we demon-
strate that over-expression of DN-JAK2 completely
inhibits IL-5-induced activation of both JAK2 and
JAK1, tyrosine phosphorylation of Oc, and cell
proliferation.76),89)Overexpression of DN-JAK1 com-
pletely inhibits JAK1 activation, but it does not
suppress JAK2 activation. These results imply that
JAK2 activation is critical and indispensable for
inducing tyrosine-phosphorylation of Oc and activa-
tion of JAK1.
It is worthwhile to note that inhibition of Oc
proteasome degradation results in prolonged activa-
tion of Oc, JAK2, STAT5, and SHP-2 in which JAK
kinase activity is required for the direct ubiquitina-
tion of the Oc cytoplasmic domain and proteasome
(2) Btk activation. Btk is the gene responsible
for human X-linked agammaglobulinemia (XLA),
which is characterized by a near absence of peripheral
B cells, low concentrations of serum Igs and varying
degrees of bacterial infections.102)Btk is a cytoplas-
mic tyrosine kinase expressed in myeloid, erythroid
and B lineage cells except plasma cells. IL-5 induces
tyrosine phosphorylation and activation of Btk in an
Fig. 7. IL-5R, expression of on progenitors of B-1 cells and eosinophils. Mouse eosinophil progenitors in the fetal liver express IL-5R,.
However B-1 cell progenitors in the fetal liver do not express IL-5,, although B-1 cell progenitors in the bone marrow express IL-5,.87)
[Vol. 87, 474
Fig. 9.Signal transduction through IL-5R. (A) Comparison of amino acid residues among IL-5R,, IL-3R,, and GM-CSFR, and their
functional domains.41),70)(B) Molecular basis of IL-5 signal transduction in human eosinophils. IL-5 stimulation of eosinophils
activates JAK2/STAT5 and Ras–MAP kinase pathways leading to induction of the expression of genes involved in eosinophil growth,
survival, and activation.76)Activation of JAK2 is critical for IL-5 signaling. Spred-1 is a negative regulator of Erk activation and
regulates IL-5-induced eosinophil activation. (C) IL-5 stimulation of mouse B cells activates three different signaling pathways,
namely JAK2/STAT5, Btk, and Ras–MAP kinase leading to induction of the expression of genes involved in B cell proliferation and
survival, and differentiation.
Fig. 8. Schematic illustration of our model regarding transcriptional regulation of the mIL-5R, gene. The mIL-5R, gene has multiple
promoter regions. The region from !250 to !115 of mIL-5R, gene is important for B-cell-specific transcriptional activation.
Nucleoproteins binding to the !250 to !115 region are specifically detected in mIL-5,DB cell lines and activated B cells. E12/E47,
C/EBPO, Sp1, Oct-2, and unknown protein bind to the region and participate in transcriptional activation.90)Binding of C/EBPO to
the !250–!115 region is found in eosinophils.
IL-5 in the immune system and inflammationNo. 8] 475
IL-5-dependent mouse pro-B cell line.94),103)A spon-
taneous mutation of Btk (a single amino acid
mutation at R28C in the pleckstrin-homology do-
main) in mice produces X-linked immunodeficiency
(xid). The B cells from XID and Btk!/!mice show
impaired B cell development and hyporesponsiveness
to IL-5, IL-10, and LPS and fail to proliferate in
response to stimulation via the BCR or CD38.95)
Activated B cells from transgenic mice expressing IL-
5R, in the xid background do not respond to IL-5 for
differentiation into IgG-ASC.95)It is not clear
whether Btk is involved in IL-5 signaling in human
peripheral B cells or whether the B-cells from XLA
patients respond to IL-5, because human peripheral
B cells from healthy volunteers express few IL-5R,,
We identified Btk-associated
(BAM)11, which binds to the pleckstrin-homology
domain of Btk.104)BAM11 is a murine homologue of
human LTG19/ENL, a fusion partner of MLL/ALL-
1/HRX, in infantile leukemia cells. Forced expression
of BAM11 in B cell progenitors inhibits Btk activity
and IL-5-induced proliferation. BAM11 may nega-
tively regulate Btk-dependent mouse B cell trigger-
ing. BAM11 has transcriptional co-activator activity
that is enhanced by Btk through pleckstrin-homology
and the kinase domain of Btk105)(Fig. 9C). As
BAM11 is co-immunoprecipitated with the INI1/
SNF5 protein, a member of the SWI/SNF complex,
IL-5 might regulate gene transcription in B cells by
activating Btk, BAM11 and the SWI/SNF transcrip-
Eosinophil progenitors in the bone marrow and
mature eosinophils in the periphery of XID mice fully
respond to IL-5 and proliferate in vivo, indicating
that Btk activation may be dispensable for IL-5
signaling in eosinophils. It is not yet clear whether
mature eosinophils or eosinophilic precursors from
XLA patients respond to IL-5 for proliferation or
(3) Ras/ERK activation.
ellular signal-regulated kinase (ERK) pathway has
been implicated in signaling of IL-5 for maintaining
cell-survival, proliferation and differentiation of
eosinophils (Fig. 9B and 9C).106)Sprouty family
proteins are identified as negative regulators for
growth factor-induced ERK activation. Yoshimura
and his colleagues cloned the Sprouty-related Ena/
(Spred)-1 and identified it as a negative regulator of
growth factor-mediated, Ras-dependent ERK activa-
tion. They also demonstrated that Spred-1 negatively
regulated allergen-induced airway eosinophilia and
hyperresponsiveness, without affecting THcell differ-
entiation.107)Spred-1 could suppress IL-5-dependent
cell proliferation and ERK activation. Moreover,
Spred-1 deficiency showed overexpression of IL-13 in
eosinophils. Spred-1 is a negative regulator of ERK
activation and may modulate eosinophil activation
normally mediated by IL-5 (Fig. 9B).
5. IL-5 modulates acquired immune response
(1) Enhancement of B-2 differentiation into
ASC. Signaling through CD40 in combination with
T cell-derived cytokines enhances B-2 cell differ-
entiation, accompanied with IgH class switch recom-
bination (CSR), into the generation of ASC. In mice,
ASC formed in vivo can be identified by their high
expression of syndecan-1 (CD138) in conjunction
with low B220. Syndecan-1Dcells display a gene
expression profile of plasma cells, with increased
expression of the J chain, B lymphocyte-induced
maturation protein 1 (Blimp-1) and X-box-binding
protein 1 (Xbp-1), while expressions of AID, B cell
lymphoma 6 (Bcl-6) and Pax5 are decreased.12),108)
In the mouse, IL-4 is a survival factor for B-2
cells and an inducer of CSR, primarily to IgG1 and
IgE. In contrast, IL-5 acts to increase the likelihood
of differentiation of B-2 cells in the spleen into IgM-,
IgG- and IgA-producing ASC and synergizes with IL-
4. For example, IL-5 acts on sIgADB-2 cells, but not
on sIgA!B cells in Peyer’s patches and to a lesser
extent in the spleen to induce IgA production.86),109)
As IL-5 induces neither the expression of germ-line
C, transcripts nor the formation of IgA-specific
switch circular DNA, IL-5 is not a class switching
factor for IgA. Rather IL-5 acts on the B cells
committed to become IgA-ASC and induces their
terminal differentiation. TGF-O is an inducer of CSR
for C7 to C,.109)
(2) Induction of class switch recombination
to C7 to C.1.
Naïve B cells undergo CSR and
develop into ASC to generate the appropriate class
and amount of antibody necessary for effective
immunity. CSR results in replacement of the C7
heavy chain constant region with other CHsequences
in activated B cells. Cytokines and mitogens are able
to rapidly and selectively up-regulate steady-state
levels of specific germline CHRNA. CSR between S7
and another S region 5′ to a CHsequence includes
looping out and deletion of all CHgenes except for
the one being expressed. For example, CSR from IgM
to IgG1 requires B-cell proliferation, .1 germline
expression, 7 to .1 DNA recombination, and DNA
[Vol. 87, 476
repair. The involvement of AID that attacks DNA
directly or indirectly through RNA editing has been
demonstrated in the regulation or catalysis of the
DNA modification step of CSR.8)–10),106)Several
proteins besides AID such as Bach2, uracil-DNA
glycosylase (UNG), and 53BP1 are also involved in
We have demonstrated that IL-5 induces the
maturation of CD40- and CD38-activated B cells to
IgG1-ASC.112)The CD38 stimulation of B cells
induces the expression of germline .1 transcripts,
NF-5B/Rel activation, and enhancement of IL-5R,
expression.113)IL-5 stimulation of CD38-activated B
cells further induces cell cycle progression and
increase in frequencies of 7 to .1 CSR.97),112)This
IL-5-dependent 7 to .1 DNA CSR is totally IL-4
independent and associated with the enhanced gene
expression of AID, UNG, Bach2 and 53BP114)–116)
and with the activation of Ku70, Ku80, and DNA-
PKcs that are essential for DNA repair. The IL-5-
induced 7–.1 CSR and IgG1 production is totally
dependent on STAT5 activation.97)Carboxy-termi-
nus of IL-5R, is required for the IL-5-induced IgG1
production (Fig. 9A).
We conducted comprehensive analyses of the
expression of IL-5-inducible genes in CD38-stimu-
lated mouse B cells using a microarray system. A
set of genes including BCL6, Aid, and Blimp-1 is
critically regulated by IL-5114)(Fig. 10). These genes
are prone to be induced slowly after IL-5 stimulation.
The Blimp-1 and Aid expression are upregulated
from 24hrs after the IL-5 stimulation,115)while BCL6
mRNA levels decline within 6hrs of IL-5 stimulation.
Significant levels of the J chain and .1–7 reciprocal
circular DNA expression are detectable around 48hrs
after IL-5 stimulation.114)
6. IL-5 in health and diseases
Emerging concepts in understanding the role of
IL-5 in asthma have been discussed through the
integration of results from animal studies and analy-
ses of clinical disorders. The lack of bronchial hyper-
reactivity and eosinophils in the lungs of antigen-
sensitized and aeroallergen-challenged IL-5 gene
deficient or IL-5R, deficient mice strengthens the
linkage of IL-5 to the pathogenesis of asthma.117)–119)
Administration of a neutralizing mAb to IL-5 before
antigen inhalation suppresses the airway hyper-
reactivity of mouse, guinea pig and monkey mod-
els120)–122)and appears to be applicable to inhibit the
development of allergen provoked airway eosinophilia
(1) Anti-IL-5 mAb therapeutics.
philia is associated with a wide variety of conditions,
including asthma and atopic diseases, helminth
infections, and drug hypersensitivity. Case reports
and series of treatment of patients having disorders
with eosinophilia with humanized anti-hIL-5 mAbs
(mepolizumab and reslizumab) suggest promising
Fig. 10.Schematic illustrations of tyrosine kinases, signaling molecules, and transcription factors that are involved in IL-5-induced CSR
of 7 to .1 CSR and IgG1 production by activated mouse B-2 cells.89)IL-5 is produced by not only hematopoietic cells including TH2
cells, mast cells and eosinophils, but also by non-hematopoietic cells in various tissues.
IL-5 in the immune system and inflammationNo. 8]477
A. Clinical trials in bronchial asthma.
asthmatic patients, IL-5 levels are elevated in the
serum and the bronchoalveolar lavage fluid. In
addition, increased eosinophil numbers and airway
hyperresponsiveness are observed upon IL-5 inhala-
tion by asthmatic patients. Leckie and coworkers
have shown that an administration of humanized
anti-IL-5 mAb, mepolizumab to patients with mild
asthma caused decrease in numbers of peripheral
blood and sputum eosinophils, although mepolizu-
mab exhibited no significant improvement in asthma
symptoms.123)The second humanized anti-hIL-5
mAb, reslizumab is also shown to decrease blood
eosinophil counts, but no significant improvement is
observed in asthma symptoms or lung function in
patients with severe asthma.
A large-scale clinical trial of mepolizumab in
patients with moderate persistent asthma also
showed that it was ineffective in improving asthma
symptoms.124)As eosinophils downregulate their IL-
5R surface expression, tissue eosinophils may survive
in the absence of IL-5. Therefore, it is desirable to
develop a stronger intervention of eosinophil tissue
accumulation and survival for depletion of eosino-
phils from asthmatic tissues.
B. Clinical trials in hypereosinophilic syndromes.
Hypereosinophilic syndrome (HES) comprises a
heterogeneous group of disorders characterized by
persistent peripheral eosinophilia for a minimum of
6 months, lack of evidence for other causes of
eosinophilia, and organ damage and dysfunction
associated with eosinophil infiltration.125)An inter-
stitial deletion on chromosome 4q12 resulting in the
formation of the Fip1-like 1–platelet-derived growth
factor receptor , fusion gene leads to generation of
FIP1L1–PDGFRA fusion protein. The FIP1L1–
PDGFRA rearrangement results in a constitutively
activated platelet-derived growth factor and repre-
sents a subset of chronic eosinophilic leukaemia.
Rothenberg and his colleagues evaluated the effect
of mepolizumab on HES patients negative for
FIP1L1–PDGFRA by an international, multicenter
randomized, double-blind, and placebo-controlled
trial. They showed that mepolizumab treatment
enabled clinically significant reduction in the cortico-
steroid dose, often corticosteroid discontinuation,
in HES patients negative for FIP1L1-PDGFRA
without major safety concerns.126)This provides an
example of successful therapy targeting eosinophils
in eosinophil-mediated disorders.
(2) Anti-human IL-5R, mAb therapy.
eosinophil precursors and mature eosinophils con-
stitutively express IL-5R,, it is worthwhile attesting
the potential of humanized anti-hIL-5R, mAb for
eliminating eosinophils localized in the inflammatory
tissues by antibody-dependent cell-mediated cyto-
toxicity (ADCC). Koike and his colleagues developed
humanized anti-hIL-5R, mAb, KM1259, which
exerted potent inhibitory activity on IL-5.127)They
also developed a humanized fucose-negative anti-hIL-
5R, mAb (known as MEDI-563), which is recombi-
nant IgG1 mAb and binds with high affinity to the
IL-5R,. MEDI-563 inhibits proliferation of IL-5-
dependent cell lines by blocking the IL-5 binding to
the IL-5R, and shows augmented eosinophil apop-
tosis in vitro via ADCC. Afucosylation enhances the
interaction of MEDI-563 with Fc.RIIIa, the main
activating Fc. receptor (Fc.R) expressed on natural
killer (NK) cells, macrophages and neutrophils,128)
and heightens ADCC functions by more than 1,000-
fold over the parental antibody. In non-human
primates MEDI-563 depleted blood eosinophils and
eosinophil precursors in the bone marrow.129)
Busse and his colleagues assessed the safety
profile, biological effects andpharmacokinetic activity
of MEDI-563.130)They reported that adult patients
with mild atopic asthma received single escalating
doses of intravenous injection of MEDI-563 had
an acceptable safety profile and resulted in marked
reduction of peripheral blood eosinophil counts within
24hrs of dosing at the levels of tested up-to 3mg/Kg.
Although the effect of MEDI-563 on eosinophils
was reported to persist for 8–12wks post dosing, no
deteriorations of lung function were shown. Their
results indicate that single escalating doses of MEDI-
563 have an acceptable safety profile and result
in marked reduction of peripheral blood eosinophil
counts within 24 hours of dosing. This effect persisted
for at least 2 to 3 months in subjects dosed in the
0.03mg/kg to 3mg/kg range. So far no side-effect of
MEDI-563 on B cells have been reported.130)
7. Future perspectives
IL-5 is an interdigitating homodimeric glycopro-
tein and a member of the four , helical bundle motifs
that are conserved among hematopoietic cytokines.
IL-5 exerts its effects on target cells via IL-5R,
comprising an IL-5, and Oc subunit. The membrane
proximal PPXP motif of the cytoplasmic domain of
both the IL-5R, and Oc subunit is essential for IL-5
signal transduction. Elucidation of the functional
residues on IL-5 and IL-5R subunits will expedite the
design and development of therapeutic antagonists
and agonists of IL-5-mediated immune responses.
IL-5 has pleiotropic effects on various cell types
and controls the production and function of myeloid
and lymphoid cells. In mice, the role of the IL-5/
IL-5R system in the production and secretion of IgM
and IgA in mucosal tissues is highly appreciated. In
humans, IL-5 acts mainly on eosinophils and their
precursors; however hIL-5 might also play a crucial
role in the production of IgA in human mucosal
tissues. Structural, functional and clinical studies
provide insight into the role of IL-5 and its receptor
system in the immune response, inflammation, and
disease control (Fig. 11). We also emphasize the
strong impetus for investigating the means of IL-5
regarding linkage between natural and adaptive
immunity specific to the epitope of natural ligands
and exogenous allergens.
In aggregate, the structural, functional, and
clinical studies described herein provide insight into
the role of hIL-5 in health and diseases, and a strong
impetus for investigating the means of modulating
IL-5 effects. In concert with the efficacy of anti-hIL-5
and anti-hIL-5R, antibody therapy in hypereosino-
philic syndrome, entirely new approaches and con-
cepts regarding patient care may emerge in the near
I am grateful to my collaborators for their
tremendous contribution during the course of this
study and sharing data with them. Our project was
supported in part by a Grant-in-Aid for Scientific
Research for Special Project Research, Cancer Bio-
science, and Special Coordination Funds for promot-
ing Science and Technology from the Ministry of
Education, Science, Sports and Culture, and by
Long-term Research Initiatives from Foundation of
Japan Industrial Association. Department of Immu-
nobiology and Pharmacological Genetics, Graduate
School of Medicine and Pharmaceutical Science,
University of Toyama is supported by Toyama
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(Received Feb. 16, 2011; accepted June 3, 2011)
Kiyoshi Takatsu is the Director of Toyama Prefectural Institute of Pharmaceutical
Research and Endowed Professor of Department of Immunobiology and Pharmacological
Genetics at the Graduate School of Medicine and Pharmaceutical Science, University of
Toyama. He is also Emeritus Professor of the University of Tokyo. He was born in 1944,
trained at the Institute of Cancer Research, Graduate School of Medicine, Osaka
University, and received Ph.D. in Medical Research in Osaka University in 1973. He was
appointed in 1982 as Professor of School of Division of Immunobiology, the Institute of
Medical Immunology at the Graduate School of Medicine, University of Kumamoto from
1982 to 1992. Then he was appointed as Professor of Immunology, Department of
Microbiology and Immunology at the Institute of Medical Science, the University of
Tokyo from 1991 to 2007. His research interests are Immunobiology, in particular the regulation of antibody
production by T-cell-derived soluble products, adjuvant activity of Ag85B and its peptide secreted by
Mycobacterium tuberculosis on cytotoxic T cell response, and discovery of useful natural compounds from
medicinal plants. His work has led to the discovery of IL-5 and its receptor. He is a recipient of Academic Award of
the Mochida Memorial Foundation (1992). the Hideyo Noguchi Memorial Award For Medical Sciences (2003), and
Paul Ehrlich Award from International Eosinophil Society (2007). He was also elected as a Fellow of the American
Association for the Advancement of Science (1992).
IL-5 in the immune system and inflammationNo. 8] 485