The role of immune semaphorins in multiple sclerosis
Tatsusada Okunoa,b,c, Yuji Nakatsujia, Atsushi Kumanogohb,c,d,⇑
aDepartment of Neurology, Osaka University Graduate School of Medicine, Osaka, Japan
bDepartment of Immunopathology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
cWorld Premier International Immunology Frontier Research Center, Osaka University, Osaka, Japan
dDepartment of Respiratory Medicine, Allergy and Rheumatic disease, Osaka University Graduate School of Medicine, Osaka, Japan
a r t i c l e i n f o
Received 28 February 2011
Revised 15 March 2011
Accepted 16 March 2011
Available online 22 March 2011
Edited by Richard Williams, Alexander
Flügel and Wilhelm Just
Multiple sclerosis (MS)
a b s t r a c t
The nervous and immune systems have similar functional characteristics. Both have an intricate net-
transduction. Although semaphorins were originally identified as guidance cues in neural develop-
ment, accumulating evidence indicates that several semaphorins called ‘immune semaphorins’, such
asSema3A,4A,4D, 6Dand 7A,are critically involved invarious phasesof theimmuneresponse by reg-
ulating immune cell–cell contacts or cell migration. In this review, we present recent knowledge on
the functions of semaphorins and their receptors in the immune system and their potential roles in
the pathogenesis of multiple sclerosis (MS), a representative CNS autoimmune disease, and its animal
model, experimental autoimmune encephalomyelitis (EAE).
? ? 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
Semaphorins, named after the system of signaling flags used in
maritime communications, were originally described as chemore-
pulsive cues that were required to guide neuronal axons to the
appropriate targets. Since semaphorins and their functions were
originally discovered in the early 1990s, more than 20 types of
these proteins have been identified . Although they have been
largely studied as axonal guidance cues, semaphorins are currently
known to have pleiotropic and important functions in other phys-
iological and pathogenic processes, including heart development
, vascular growth, tumor progression  and immune cell regu-
Studies on the roles of semaphorins in neurological disorders
have examined these molecules from two perspectives, as guidance
molecules in CNS development or regeneration and as immune reg-
ulators. Semaphorins have been shown to be aberrantly expressed
during pathogenesis in the CNS. For example, Sema3A has been
shown to be expressed in neurons during Alzheimer’s disease and
at the neuromuscular junction in amyotrophic lateral sclerosis
(ALS) [5,6]. Increased Sema3A and 3F expression was observed
around MS lesions in the brain, where Sema3A and 3F respectively
act as a repellant and attractant for oligodendrocyte precursor cell
(OPC) migration . Sema4D, an inhibitor of axonal growth, is up-
regulated in oligodendrocytes after spinal cord injury . Thus,
these findings suggest that these semaphorins participate in the
pathology of neurological disorders as inhibitors/accelerators of
On the other hand, semaphorins have also been shown to have
various immune regulatory functions, in terms of immune cell–cell
contacts and immune cell trafficking. Sema4D was the first
semaphorin that was determined to have roles in the immune sys-
tem . Since this seminal study, other semaphorins, such as Se-
ma3A, Sema4A, Sema6D and Sema7A, have been shown to have
crucial roles in pathogenic immune responses in EAE [10–14], an
animal model of MS (Fig. 1).
Multiple sclerosis (MS) is an inflammatory demyelinating dis-
ease of the CNS. The number of MS patients has been increasing,
disease . As younger females are more susceptible, MS is a lead-
ing cause of neurological disabilities in young adults. Although the
cur in genetically predisposed individuals after they are exposed to
an environmental trigger that stimulates myelin-specific T cells
[16,17]. Indeed, the IL-2 receptor and MHC class II were shown to
be associated with disease susceptibility in genome-wide associa-
tion studies . Thus, antigen presentation and subsequent T-cell
0014-5793/$36.00 ? 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
⇑Corresponding author at: Department of Immunopathology, Research Institute
for Microbial Diseases, Osaka University, 3-1 Yamada-oka, Suita, Osaka 565-0871,
E-mail address: email@example.com (A. Kumanogoh).
FEBS Letters 585 (2011) 3829–3835
journal homepage: www.FEBSLetters.org
activation are essential for the onset of MS. In addition, CD4+ T-cell
differentiation and transmigration through the blood-brain barrier
cells, as well as cell migration play crucial roles in the pathogenesis
of MS (Fig. 2). Because semaphorins have been shown to regulate
these processes, it is plausible that they are involved in the patho-
genesis of MS. In this review, we focus on the immune regulatory
functions of these semaphorins with particular emphasis on their
relationship with the representative neuroimmunological disease
MS and its animal model EAE.
2. EAE and MS
In this review, we described the function of immune semapho-
rins and their possible relevance to MS on the basis of the experi-
mental findings obtained from EAE. EAE reflects some of the
pathogenic, clinical, and therapeutic features of MS, thereby pro-
viding some insight into the molecular and cellular basis. However,
the findings obtained from EAE experiment do not always reflect
MS [17,20]. Indeed, we described the possible involvement of
semaphorins in the initial inflammation of MS rather than demye-
lination and degeneration in this review.
3. Semaphorins and their receptors
The semaphorin family includes secreted and membrane-
associated proteins that are characterized by a conserved amino-
terminal ‘‘Sema’’ domain. Semaphorins range in size from 400 to
1000 amino acid residues, depending on additional C-terminal
sequence motifs such as an immunoglobulin domain, thrombo-
spondin domain, or glycosylphosphatidylinositol (GPI) linkage site.
Based on structural elements and amino acid sequence similarities,
the semaphorin family has been further classified into eight sub-
classes. Invertebrate semaphorins are grouped into classes I and
II, whereas classes III–VII are expressed in vertebrates. Addition-
ally, some DNA viruses encode functional semaphorin proteins.
Semaphorins in classes I and IV–VII are membrane-associated,
whereas those in classes II and III and the viral semaphorins are se-
creted . Two groups of proteins, plexins and neuropilins, have
been identified as the primary receptors for semaphorins. Most
membrane-bound semaphorins directly bind plexins, but class III
semaphorins require neuropilins as obligate co-receptors [21,22].
However, recent reports have demonstrated that receptor usage
by semaphorins is more complex than was previously imagined.
For example, Sema7A utilizes integrin receptors to exert its func-
tion, and Sema3E signals independently of neuropilin through
Representative immune semaphorins
Neuronal axon guidance
Activation of DCs,
Formation of the
Neuronal axon guidance
Secreted semaphorinMembrane-type semaphorin
Fig. 1. Representative immune semaphorins and their receptors in lymphoid and non-lymphoid cells. Sema3A is a secreted semaphorin, whereas Sema4D, 4A, 6D and 7A are
membrane-associated semaphorins. Sema3A binds to neuropilin-1 to assemble a NP-1/plexin-A1 receptor complex and is involved in axon guidance. Sema4D binds to plexin-
B1 to transduce chemorepulsive signals in the CNS. In the immune system, CD72 or plexin-B1 serves as the functional receptor for Sema4D in B cells, DCs and microglia and
enhances the activation of these cells. Sema4A associates with TIM-2 and is involved in T-cell activation and differentiation in the immune system. In the vascular system,
however, Sema4A recognizes plexin-B proteins and plexin-D1. Sema6D induces different biological activities through plexin-A1, depending on its co-receptors. During chick
cardiogenesis, plexin-A1 differentially binds to Off-track and VEGFR2, and these receptor complexes have distinct functions in heart morphogenesis. In the immune system,
plexin-A1 forms a receptor complex with TREM-2 and DAP12, and upon Sema6D binding, this complex transduces signals that stimulate DCs and osteoclasts. Sema7A uses b1
integrin as a receptor in both the nervous and immune systems. In the immune system, Sema7A is expressed on activated T cells and stimulates macrophages through a1b1
integrin to promote inflammatory reactions. DC, dendritic cell; DAP12, DNAX-activating protein 12; NP-1, neuropilin-1; OTK, Off-track kinase; TIM-2, T-cell immunoglobulin
and mucin domain-containing protein 2; TREM-2, triggering receptor expressed on myeloid cells 2; VEGFR2, vascular endothelial growth factor receptor 2.
T. Okuno et al./FEBS Letters 585 (2011) 3829–3835
plexin-D1 in both the nervous and immune systems [23,24]. Some
plexins further associate with various co-receptors to exert the
diverse functions of semaphorins. Additionally, in the immune sys-
tem, two molecules unrelated to plexins and neuropilins, CD72
 and T-cell immunoglobulin and mucin domain protein-2
(TIM-2) , functionally interact with Sema4D and Sema4A,
respectively (Fig. 2).
4. Plexins and semaphorin–plexin signaling
The physiological functions of semaphorins are mediated
through a family of transmembrane receptors called plexins, which
are classified into four sub-families plexin-A1-4, plexin-B1-3, plex-
in-C1 and plexin-D1 . In the nervous system, small GTPases,
including Rho, Rac, R-Ras and Rnd1, have been shown to play cru-
cial roles in mediating diverse neural functions through semapho-
rin–plexin signaling . One of the most important and common
plexin signaling pathways is mediated by the ability of plexin to
exert R-Ras GAP (GTPases activating protein) activity and associate
with Rnd1 [27–29]. Rnd1 binds to a linker region between the
highly conserved C1 and C2 subdomains in the cytoplasmic tails
of plexins. Rnd1 binding to the region between the C1 and C2
domains allows plexins to function as R-Ras GAPs. Therefore, sem-
aphorin-induced clustering of the plexin-Rnd1 complex promotes
the down-regulation of R-Ras activity, leading to reduced inte-
grin-mediated cell adhesion and growth cone collapse. Aside from
controlling integrin-mediated attachment through R-Ras activity,
plexin-B1 also mediates axon guidance by regulating the activities
of RhoA through PDZ-Rho guanine nucleotide exchange factors and
However, only the plexin-B subfamily has been shown to bind
to PDZ-RhoGEF/LARG,and PDZ-RhoGEF/LARG-mediated
activation is not a common signaling pathway for the plexin fam-
ily. In addition to the machineries described above, plexins are
reportedly involved in actomyosin contraction  and microtu-
bule destabilization [32,33].
In addition to small GTPases, plexins can associate with different
co-receptors, including cytoplasmic/receptor-type protein kinases
in distinct tissues, which allows semaphorins to exert diverse func-
tions. For instance, plexin-A1 is associated with the tyrosine kinase
the other hand, plexin-A1 forms a receptor complex with TREM-2/
DAP12 during osteoclastogenesis . Furthermore, plexin-B1 has
been shown to associate with the receptor tyrosine kinases Met
and ErbB2, triggering the invasive growth of epithelial cells .
5. Immune semaphorins: regulation of immune cell–cell
contacts and migration
There are a number of similarities between the nervous and im-
mune systems. Both systems consist of highly organized networks
that interact with each other using shared molecules such as
chemical mediators and cytokines . The immune response is
composed of a series of cell–cell contacts, including interactions be-
tween T cells and antigen-presenting cells (APCs), such as B cells,
macrophages and dendritic cells (DCs). These types of cell–cell con-
tact activate immune responses that are characterized by the clonal
expansion and development of effector T cells, in which the T-cell
receptor (TCR) closely contacts the cognate antigen peptide-major
histocompatibility complex on the APC surface. This structure is
ical synapse’’. A number of membrane-associated semaphorins or
their receptors are known to function as co-stimulatory molecules
that regulate the immunological synapse. For example, plexin-A1
MS pathogenesis and involvement of semaphorins
Blood Brain Barrier
CD4+ T cells
CD4+ T cells (Th1/Th17)
Peripheral Immune System
Fig. 2. Models of the significance of immune semaphorins in the pathogenesis of MS. During the priming phase in the periphery, T cell-derived Sema4D or Sema6D enhances
DC activation and maturation through CD72 and plexin-A1, respectively, that then contribute to the generation of myelin-specific T cells. Sema3A can promote the
transmigration and subsequent invasion of immune cells, including DCs, into the CNS. After these immune cells invade the CNS, Sema4D or Sema7A from effector CD4+ T cells
interacts with plexin-B1or VLA-1 expressed on microglia/macrophages, respectively, and increases the production of inflammatory molecules, including nitric oxide (NO) and
cytokines that are toxic to oligodendrocytes. OLG; oligodendrocytes.
T. Okuno et al./FEBS Letters 585 (2011) 3829–3835
is recruited to lipid rafts on DCs that accumulate at the immunolog-
ical synapse between T cells and DCs and affects T-cell priming .
In addition, Sema7A in activated T cells is recruited to the immuno-
with integrin receptors to promote inflammatory cytokine produc-
mulates at contact sites between basophils and CD4+ T cells,
data suggest that membrane-type semaphorins play critical roles in
T cell–APC interactions by regulating the immunological synapse.
In addition to cell–cell contacts, recent evidence indicates that
several semaphorins function as navigators for migrating immune
cells in both primary and secondary lymphoid organs. In the ner-
vous and cardiovascular systems, semaphorin–plexin signaling
regulates cytoskeletal dynamics by activating GTPases, resulting
in the modulation of integrin-mediated cell adhesion and actomy-
osin contractility . In this context, it is possible that semapho-
rins also regulate immune cell trafficking using similar machinery.
In fact, we recently found that Sema3A induces phosphorylation of
the myosin light chain (MLC) to promote actomyosin contraction
through the plexin-A1/neuropilin-1 complex, which resulted in
greater DC transmigration as these cells passed through narrow
gaps. Consistently, when plexin-A1-deficient DCs were adoptively
transferred into the dermis of oxazolone-treated mice, they were
retained along the lymphatics due to their impaired transmigration
across the lymphatics . In addition, Sema3E, which interacts
with plexin-D1 in a neuropillin-1-independent manner, partici-
pates in thymocyte development by regulating thymocyte migra-
tion. Sema3E binds to positively selected CD69+ double positive
(DP, CD4+, CD8+) thymocytes and inhibits CCL25-mediated migra-
tion towards corticomedullary junctions in the thymus. Consistent
with this function, Sema3E-deficient mice have an abundance of
CD69+ DP thymocytes in the cortex and disrupted corticomedul-
lary junctions . In contrast to the association between mem-
brane type semaphorins and cell–cell contact, these data suggest
that secreted-type class III semaphorins are critically involved in
immune cell trafficking.
Taken together, accumulating evidence indicates that immune
semaphorins regulate immune cell–cell contacts and migration,
leading to proper immune responses.
6. ‘Immune semaphorins’ involved in cell migration
6.1. Sema3A, neuropillin-1 and plexin-A1
Sema3A is a representative secreted-type semaphorin and it is
well documentedthat Sema3Afunctions as an axon guidance mole-
cule. Interestingly, Sema3A has been shown to be aberrantly ex-
pressed in brains with MS , suggesting that Sema3A is involved
in the regeneration of oligodendrocytes or axons. Sema3A directly
binds to neuropilin-1, which induces the activation of plexin-A pro-
teins and the transduction of axon guidance signals. In the immune
system, plexin-A1 is expressed in DCs. We recently demonstrated
that Sema3A produced in the lymphatics functions as a ligand for
the plexin-A1–neuropilin-1 receptor complex expressed by DCs
, leading to greater DC transmigration as these cells passed
through narrow gaps. These results suggest that Sema3A is not only
an axon guidancemoleculein the CNS but also an important regula-
tor of immune cell migration.
6.2. Sema3A and EAE/MS
As described above, lack of Sema3A/neuropilin-1/plexin-A1
interactions results in impaired DC migration to the draining lymph
nodes after immunization, leading to impaired antigen-specific
T-cell priming. In addition, Sema3A is suggested to inhibit OPCs
migration to the demyelinated lesions in MS. Indeed, immunizing
plexin-A1-deficient mice with the MOG peptide in Freund’s com-
plete adjuvant (CFA) results in less severe EAE, which is consistent
cent evidence has shown the significance of immune cell migration
in MS therapy. Fingolimod (FTY 720) or anti-a4b1integrin (VLA4),
ropillin-1/plexin-A1 interactions has beneficial roles in both reduc-
ing immune cell invasion and increasing remyelination.
7. ‘Immune semaphorins’ involved in T cell–APC interactions
was the first semaphorin shown to have immune regulatory func-
tions. In the immune system, Sema4D is abundantly expressed in
and DCs but is markedly up-regulated after cellular activation .
Regarding the Sema4D receptors, plexin-B1 [21,39] and CD72 
B1. On the other hand, CD72 contains two immunoreceptor
tyrosine-based inhibitory motifs (ITIM) in its cytoplasmic domain
atively regulates B cells by recruiting a tyrosine phosphatase SHP-1
is dissociated from CD72, resulting in B-cell activation . Se-
ma4D-deficient mice have impaired antibody production , indi-
cating that Sema4D is involved in B-cell activation.
In addition to its role in B-cell responses, Sema4D also exerts a
role in T-cell responses by activating DCs . Sema4D expressed
on T cells interacts with its cognate receptor on DCs to promote DC
activation and maturation, resulting in enhanced T-cell activation.
generation. Although Sema4D is a transmembrane protein, the
extracellular region is proteolytically cleaved from the surface of
activated lymphocytes through a metalloprotease-dependent pro-
cess . Sema4D is also cleaved from the surface of platelets by
themetalloprotease ADAM17. ElevatedlevelsofthesolubleSe-
lymphocytes and in the sera of either immunized or autoimmune
mice and patients with systemic sclerosis [41,43]. Interestingly,
soluble Sema4D levels are increased in the cerebrospinal fluid of
patients with HTLV-1-associated myelopathy (HAM) . T cell-
derived Sema4D was shown to induce microglia-mediated inflam-
mation or neural cell damage through microglial or neural
plexin-B1, suggesting that Sema4D has a pathological role within
the CNS [39,44].
7.2. Sema4D and EAE/MS
As described earlier, Sema4D expressed on T cells is crucially in-
volved in the initial activation of T cells through the maturation of
DCs. When Sema4D-deficient mice are immunized with a MOG
peptide in CFA, they exhibit attenuated EAE. CD4+ T cells from
the draining lymph nodes of immunized Sema4D-deficient mice
exhibit impaired antigen-specific T-cell responses, particularly
the generation of cytokine-producing effector cells, after in vitro
antigen restimulation. These observations indicate that Sema4D
is involved in the pathogenesis of EAE during the interaction
between T cells and DCs . In addition to the priming phase,
we recently found that T cell-derived Sema4D also contributes to
T. Okuno et al./FEBS Letters 585 (2011) 3829–3835
neuroinflammation by activating microglial cells through plexin-
B1. When MOG-specific T cells derived from wild-type mice were
adoptively transferred into plexin-B1-deficient mice or bone mar-
row chimera mice with plexin-B1-deficient CNS resident cells, EAE
development was considerably attenuated. Consistently, when
anti-Sema4D blocking antibodies were administered after disease
onset, this treatment significantly inhibited neuroinflammation
during EAE development . In addition, T cell-derived Sema4D
causes the collapse of process extensions in immature oligoden-
drocytes and the death of immature neural cells . Collectively,
these findings indicate that inhibiting the function of T cell-derived
Sema4D is potentially a valuable therapeutic target for MS, because
it will not only prevent the generation of encephalitogenic T cells
but also ameliorate inflammation and neural damage even after
Sema4A is constitutively expressed on DCs and up-regulated after
activation . Sema4A is also expressed in activated T cells and T
helper type 1 (Th1)-polarized cells . DC-derived Sema4A and T
cell-derived Sema4A play different roles during immune responses.
DC-derived Sema4A is crucial for antigen-specific T-cell priming,
whereas T cell-derived Sema4A is involved in helper T-cell differen-
tiation . Indeed, the phenotypes of Sema4A-deficient mice illus-
trate the critical roles of Sema4A in the differentiation of helper T
cells. Sema4A-deficient mice exhibit impaired responses to heat-
killed Propionibacterium acnes, a Th1-inducing agent. In contrast,
Sema4A-deficient mice show enhanced T helper type 2 (Th2)
responses to Nippostrongylus brasiliensis, a Th2-inducing intestinal
nematode . In addition, Sema4A-deficient mice on a Th2-prone
BALB/c background spontaneously develop atopic dermatitis (AD)
(unpublished data), supporting the notion that Sema4A is involved
in the regulation of Th1/Th2 development.
In the immune system, TIM-2 expression is induced on acti-
vated T cells . Several lines of evidence indicate that TIM-2
functions as a receptor for Sema4A. TIM-2 expression is preferen-
Administering the recombinant TIM-2 protein ameliorates EAE
development by inhibiting the generation of Th1 cells . Fur-
thermore, TIM-2-deficient mice have exacerbated lung inflamma-
tion accompanied by dysregulated Th2 responses . Taken
together, it is tempting to speculate that Sema4A-TIM-2 interac-
tions negatively regulate Th2 responses. However, there are some
phenotypic differences between Sema4A- and TIM-2-deficient
mice. For example, T cells from TIM-2-deficient mice, but not
Sema4A-deficient mice, have enhanced basal proliferation. These
observations raise the possibility that Sema4A and/or TIM-2 have
other binding partners. Indeed, T cells express plexin-B proteins
and plexin-D1, both of which can bind Sema4A .
7.4. Sema4A and EAE/MS
Since the dysregulation of helper T (Th) cells has been impli-
cated in the autoimmune pathogenesis of MS, it is plausible that
Sema4A is involved in the Th-mediated pathogenesis of MS and
EAE. Indeed, the development of MOG-induced EAE in wild-type
mice can be improved by intravenously injecting an anti-Sema4A
monoclonal antibody concurrently with MOG immunization .
The infiltration of mononuclear inflammatory cells into the spinal
cord is diminished in anti-Sema4A antibody-treated mice, in which
CD4+ T cells isolated from the draining lymph nodes have mark-
edly decreased responses to the MOG peptide. Thus, anti-Sema4A
monoclonal antibody treatment inhibits the generation of MOG
peptide-specific CD4+ T cells, leading to attenuated EAE. T helper
type 17 (Th17) cells produce IL-17 and play a critical role in inflam-
matory pathology in autoimmune diseases, including EAE and MS.
As Sema4A is critical for helper T-cell differentiation, it is plausible
that Sema4A is involved in EAE development by regulating Th17
cells, although the significance of Sema4A in Th17 cell develop-
ment has not been elucidated. Further studies will clarify the role
of Sema4A in Th17 cell development and the pathogenesis of EAE
7.5. Sema6D and plexin-A1
tor for the class VI semaphorin Sema6D . Sema6D mRNA is
iated signaling, plexin-A1 forms a receptor complex with the trig-
gering receptor expressed on myeloid cell-2 (TREM-2) and the
adaptor molecule DAP12 in DCs and osteoclasts. Plexin-A1- and
DAP12-deficient mice have impaired T-cell responses and develop
osteopetrosis [12,48], and genetic mutations in human DAP12 or
TREM-2 result in a bone fracture syndrome called Nasu-Hakola dis-
TREM-2/DAP12 complex. The function of Sema6D in DCs was eluci-
dated with an RNA interference system and analyses of plexin-A1
knockout mice. Short hairpin RNA-mediated knockdown of plexin-
A1 in DCs impairs their ability to activate T cells in vitro and
in vivo . In addition, plexin-A1-deficient DCs poorly stimulate
antigen-specific T cells , and plexin-A1-deficient mice have im-
paired T-cell priming. These observations indicate that Sema6D is
required for the initial activation and efficient generation of anti-
gen-specific T cells by DCs.
7.6. Sema6D and EAE/MS
Immunization of plexin-A1-deficient mice with the MOG
peptide in CFA results in impaired EAE development, which is con-
sistent with impaired MOG peptide-specific CD4+ T-cell responses
. Consistent with the finding that DAP12 associates with plex-
in-A1, DAP12-deficient mice exhibit attenuated development of
MOG-induced EAE and impaired generation of MOG-specific T cells
. Therefore, inhibiting Sema6D might be a therapeutic target
for MS because this would inhibit DAP12/TREM2 activation and
subsequently prevent the generation of encephalitogenic T cells.
Sema7A, also known as CD108, is a membrane-associated glyco-
sylphosphatidylinositol (GPI)-linked protein. In the nervous sys-
tem, Sema7A has been shown to promote olfactory bulb axon
outgrowth and is required for the appropriate formation of the lat-
eral olfactory tract during embryonic development . Although
plexin-C1 was initially identified as a receptor for Sema7A , Se-
ma7A has an arginine–glycine–aspartate sequence in its Sema do-
main that is a well conserved integrin-binding motif, and Sema7A
exerts axon attraction through the b1 integrin receptor and not
through plexin-C1 by activating the downstream mitogen-acti-
vated protein kinase pathway . In the immune system, Sema7A
expression is induced in activated T cells and is involved in T cell-
mediated inflammatory immune responses. Recombinant Sema7A
protein stimulates monocytes/macrophages througha1b1 integrin,
also known as very late antigen-1, inducing the activation of the
downstream mitogen-activated protein kinase pathway and the
production of proinflammatory cytokines. As a GPI-anchored pro-
tein, Sema7A is recruited to lipid rafts that accumulate at the
immunological synapse between T cells and macrophages and then
binds toa1b1 integrin. Consistently, Sema7A-deficient anda1 inte-
T. Okuno et al./FEBS Letters 585 (2011) 3829–3835
grin-deficient mice are resistant to the development of inflamma-
tion, including hapten-induced contact hypersensitivity, colitis
and EAE [13,51]. These observations indicate that interactions be-
tween Sema7A and a1b1 integrin are crucial for T cell-mediated
macrophage activation at sites of inflammation. Although plexin-
C1 is also expressed in macrophages, stimulation with recombinant
Sema7A protein induces normal proinflammatory cytokine produc-
tion by plexin-C1-deficient macrophages (unpublished data).
Therefore, at least in the context of T cell–macrophage interactions,
a1b1 integrin, but not plexin-C1, seems to be the predominant Se-
ma7A receptor . Integrin-mediated signaling is a common
mechanism by which Sema7A functions in both the nervous and
7.8. Sema7A and EAE/MS
Sema7A contributes to T cell-mediated inflammation by acti-
vating peripheral macrophages . When Sema7A-deficient mice
are immunized with the MOG peptide in CFA, the T cells are
primed normally and generate MOG peptide-specific CD4+ T cells.
However, these mice are resistant to EAE development. CD4+ T
cells from MOG-immunized Sema7A-deficient mice fail to induce
EAE when they are transferred into wild-type mice. In addition,
MOG peptide-primed CD4+ T cells from wild-type mice fail to in-
duce EAE when transferred into a1 integrin-deficient recipient
mice. Moreover, Sema7A on antigen-primed effector T cells plays
a role in inducing inflammation in EAE through interactions with
a1b1 integrin and contributes to the exacerbation of EAE .
These findings show that Sema7A is pathologically involved in
the effector phase of EAE and suggest that inhibiting Sema7A-
a1b1 integrin interactions may be a valuable therapeutic target
for MS after disease onset.
8. Concluding remarks
As immune regulators, semaphorins exert crucial roles in the
migration of APCs, differentiation of helper T cells, priming of anti-
gen-specific T cells, and modulationof inflammation. Several mech-
anisms are thought to contribute to the pathology of MS, including
the activation of CNS-reactive T cells in the peripheral immune sys-
tem, transmigration into the CNS, and reactivation and augmenta-
tion of inflammation in the CNS. There is increasing evidence that
Th17 cells, in addition to Th1 cells, are significantly involved in MS
pathology. Considering the various roles of semaphorins and the
proposed mechanisms of MS pathology, immune semaphorins
may participate at every step in the development of MS. This idea
was supported by studies on EAE. Knocking down or blocking any
of the immune semaphorins highlighted in this review attenuates
EAE severity or leads to EAE resistance. Furthermore, these results
suggest that immune semaphorins and their receptors are potential
therapeutic targets for MS.
Because immune mechanisms have also been suggested to
contribute to the pathology of other neuroinflammatory diseases,
such as Alzheimer’s disease and ALS, in addition to the autoim-
mune disease MS, it is likely that semaphorins play important roles
in these disorders at various phases. Further studies are needed to
examine the role of semaphorins in neuroinflammatory diseases,
including MS, and this research will not only help us understand
the precise pathological mechanisms but also lead to the develop-
ment of novel therapeutic strategies.
Education, Culture, Sports, Science and Technology ofJapan, grants-
in-aid from the Ministry of Health, Labor, and Welfare, the program
for Promotion of Fundamental Studies in Health Sciences of the
National Institute of Biomedical Innovation (A.K., Y.N. and S.S.),
Health and Labour Sciences Research Grants for research on intrac-
table diseases from the Ministry of Health, Labor, and Welfare (Y.N.
and S.S.), the Target Protein Research Program of the Japan Science
(A.K.) and Takeda Scientific Foundation (T.T. and A.K.).
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