Staphylococcal Pericarditis, and Liver and Paratracheal
Abscesses as Presentations in Two New Cases of
Interleukin-1 Receptor Associated Kinase 4 Deficiency
Jeannette L. Comeau, MSc,* Tong-Jun Lin, MD, PhD,* Marian B. Macken, MB BCh,† Bo Li, PhD,*
Cheng-Lung Ku, PhD,‡§ Horst von Bernuth, MD,‡§ Jean-Laurent Casanova, MD, PhD,‡§?
and Andrew C. Issekutz, MD*
Background: A deficiency in the interleukin-1 receptor activated
kinase 4 (IRAK-4) has recently been associated with severe recur-
rent, predominantly Gram-positive bacterial infections.
Clinical Presentation: Two unrelated Canadian children with
unique presentations of IRAK-4 deficiency are described. Both
children had multiple Gram-positive bacterial infections, specifically
Staphylococcus aureus and Streptococcus pneumoniae. Although
these microorganisms in patients with IRAK-4 deficiency com-
monly cause invasive infections, such as meningitis, arthritis, and
sepsis, the sites of infection in our patients were unique. In the first
patient, staphylococcal pericarditis and, on a separate occasion,
staphylococcal liver abscesses with generalized peritonitis were
presentations. In the second child, S. aureus infection caused sub-
mandibular and periauricular lymphadenitis with unsuspected para-
tracheal abscess as well. These severe infections were not accom-
panied by the expected constitutional symptoms or hematologic and
acute phase responses despite findings of advanced infection on
Methods: Cytokine production ?interleukin (IL)-6, IL-8, and tumor
necrosis factor (TNF)-?? by whole blood leukocytes and adherent
monocytes after stimulation with IL-1? or various Toll-like receptor
agonists ?lipopolysaccharide, Poly I:C, S. aureus peptidoglycan (PGN)?
was analyzed. IRAK-4 genes were sequenced by standard techniques.
Results: Failure by whole blood leukocytes to produce IL-6 or
TNF-? in response to any of these stimuli was the most consistent
finding. In striking contrast, IL-8 production in response to PGN was
normal in both cases. Both patients had novel and heterozygous
mutations and deletions in the IRAK-4 gene.
Conclusions: Our results indicate that PGN-induced IL-6 produc-
tion is via IRAK-4 dependent mechanisms, whereas IL-8 response to
PGN is via IRAK-4 independent mechanisms. Patients with rela-
tively silent but invasive bacterial infection should raise suspicion of
Key Words: infection, immunodeficiency, Toll-like receptor,
(Pediatr Infect Dis J 2008;27: 170–174)
part on the recognition of microbe-associated molecular patterns
via increasingly recognized families of molecules expressed on
immune and nonimmune cells, among which the best charac-
terized are the Toll-like receptors (TLRs). These have an intra-
cellular signaling domain that is similar to that of the interleu-
kin-1 (IL-1) receptor (TIR domain), and all TLRs except for
TLR3 signal via the IL-1 receptor associated kinase-4 (IRAK-4)
intracellular signaling molecule.1IRAK-4 is critical for signal-
ing to proceed via these receptors to activation of NF-?B
(p50/p65) and its translocation to the nucleus where it initiates
transcription of inflammatory cytokine genes.2
Recently, human IRAK-4 deficiency has been found to
be associated with invasive pneumococcal and other primarily
Gram-positive bacterial infections, characterized by a remark-
able lack of systemic, clinical, or laboratory indication of seri-
ous, often life-threatening infection.3,4Since these reports, ad-
ditional patients have been identified from various countries and
ethnic backgrounds, and an increasing variety of invasive Gram-
positive and occasionally Gram-negative bacterial infections
have been associated with this immune deficiency, usually with
serious morbidity and often fatal outcome.4–12
The full spectrum of disorders relating to these defects is
not yet clear; to date, 20 cases have been reported with the most
common pathogens being Streptococcus pneumoniae4–12and to
a lesser degree Staphylococcus aureus.4–6,8–10Common infec-
tions are meningitis,4,6,8–12arthritis, sepsis, and cellulitis.4,5,8,10
There are a few reports of Gram-negative bacterial infections
including Pseudomonas aeruginosa, Shigella sonnei, Esche-
richia coli, and Clostridium difficile,5,7however Gram-positive
he earliest host defense response to microbial invasion is
dependent on the innate immune system. This depends in
Accepted for publication August 7, 2007.
From the Departments of *Pediatrics and †Diagnostic Imaging, Dalhousie
University, Nova Scotia, Canada; ‡Laboratory of Human Genetics of
Infectious Diseases, University of Paris Rene ´ Descartes; §University
Paris Descartes, Necker Medical School; and ?Pediatric Immunology-
Hematology Unit, Necker-Enfants Malades Medical School, Paris,
Supported by Grant MT-7684 from Canadian Institutes of Health Research
(to A. C. I.), and a grant from Canadian Cystic Fibrosis Foundation (to
T.-J. L.). H. V. B. was supported by grants from the Deutsche For-
schungsgemeinschaft (VO 995/1-1 and VO 995/1-2). The Laboratory of
Human Genetics of Infectious Diseases is supported by the March of
Dimes, the BNP-Paribas Foundation, and the Schlumberger Foundation.
J.-L. C. is an International Scholar of the Howard Hughes Medical Institute.
Address for correspondence: Dr Andrew C. Issekutz, MD, Dalhousie Uni-
versity, Department of Pediatrics, Room K8518, IWK Health Centre,
5850/5980 University Avenue, Halifax, NS, Canada B3K 6R8. E-mail:
Copyright © 2008 by Lippincott Williams & Wilkins
The Pediatric Infectious Disease Journal • Volume 27, Number 2, February 2008
infections remain most common. A current IRAK-4 case regis-
try of 28 cases confirms these findings (Ku C.-L. et al, submit-
ted). Here, we report 2 new cases with hitherto undescribed S.
aureus infections associated with IRAK-4 deficiency, namely
pericarditis, peritonitis secondary to ruptured liver abscesses,
and unsuspected paratracheal abscess. The presentation and
course of these infections, the radiologic findings, response to
therapy, differential inflammatory cytokine responses to micro-
bial stimuli and IRAK-4 gene mutation in a 16-year-old male
and an unrelated 2.5-year-old female are described.
Patient 1. Patient 1 is a boy born in 1990 to a mother who was
adopted. Neither parent had any significant immunologic/infec-
tious disease history, and there was no known consanguinity.
At 14 months of age, he presented with irritability,
fever (39.5°C), and vomiting, but normal white blood cells
(WBC) at 11.9 ? 109/L with neutrophilia (90%). The cere-
brospinal fluid (CSF) leukocytes were only 270 ? 106/L
(neutrophil predominance), and glucose (4.1 mM) and protein
(0.4 g/L) were within normal range. Gram stain of CSF
showed Gram-positive cocci and S. pneumoniae as isolated.
Response to antibiotic therapy was satisfactory but residual
left-sided leg weakness remained.
At 20 months, irritability, tachypnea, and tachycardia
were noted initially with low-grade fever (38.5°C) and leukocy-
tosis (WBC ? 25.2 ? 109/L) with 73% neutrophils and 4%
bands. Investigations demonstrated S. aureus pericarditis requir-
ing pericardial drainage. Response to therapy and recovery was
At 28 months, the patient had been thought to have
staphylococcal skin infections for approximately 1 month
preceding admission for antibiotic therapy because of pre-
sumed cellulitis of the right foot. Upon presentation, redness,
swelling, and warmth were noted on the dorsum of the foot
and his temperature was 38.7°C. Antibiotic therapy resulted
in complete recovery without relapse.
At 9 years, he had intermittent abdominal pain, decreased
to continuous abdominal pain. The patient was afebrile, but
abdominal ultrasound and computed tomography (CT) scan
showed free fluid and multiple abscesses in the right lobe of the
liver. The CBC was normal with WBC of 11 ? 109/L. Lapa-
rotomy revealed generalized peritonitis caused by S. aureus
secondary to ruptured hepatic abscess. Fever (39.1°C), leukocy-
tosis (24 ? 109/L) with neutrophilia (52%) and left-shift, eleva-
tions in C-reactive protein (CRP) and erythrocyte sedimentation
rate (ESR) (71 mg/L and 60 mm/h, respectively) were observed
only after laparotomy and drain insertion into the liver abscess.
Clinical recovery was complete after 6 months of antistaphylo-
coccal antibiotic therapy with resolution of abscesses but resid-
ual scarring of the right lobe of the liver.
Immunologic workup showed that neutrophil (PMN) ni-
troblue tetrazolium dye reduction (NBT), PMN chemotaxis and
bacterial killing, alternate and classic pathway of complement
activity, serum mannose binding lectin, IgG, IgA, IgM, and IgE
were normal, although there was a borderline decrease in IgG2,
which was persistent (0.76–1.0 g/L). Specific antibody to teta-
nus and diphtheria toxoids was normal but antibody to pneumo-
coccal polysaccharide at age 9–10 years was low and increased
only after repeated immunizations with pneumococcal polysac-
charide (7-serotype)-diphtheria toxoid conjugate and then pure
pneumococcal polysaccharide (23-serotype) vaccines. Ultra-
sound of spleen was normal.
After this S. aureus abdominal infection, prophylactic
antibiotic therapy was initiated empirically with cotrimoxazole
and has been continued since 2001. The diagnosis of IRAK-4
deficiency was subsequently considered based on analysis of
IL-6 production by blood leukocytes (Table 1). There have not
been any subsequent serious infections except for 1 episode of
maxillary sinusitis in 2006, at 15.5 years, which resolved with 1
month of amoxicillin/clavulanic acid therapy.
Amplification and sequencing of the patient’s IRAK-4
gene revealed 1 allele that carries a frameshift mutation in
EXON 11 (1240Ins_A) that leads to a premature stop codon
at amino acid 413. The second allele contains a large deletion
(942-1481_1125 ? 547 del), which leads to skipping the
entire EXON 9, subsequent frame shift, and a premature stop
codon at amino acid 317.
Patient 2. Patient 2 was born in August 2004 to healthy,
unrelated parents whose relatives had no unusual immuno-
logic or infectious disease problems. The patient was well
Production of IL-6, IL-8, and TNF-? in Response to IL-1? and Microbial Stimuli
LPS PGN PICUnst.IL-1?
A: Whole blood IL-6 (pg/mL)
C: Whole blood IL-8 (pg/mL)
E: Whole blood TNF-? (pg/mL)
B: Adherent MNC IL-6 (pg/mL)
D: Adherent MNC IL-8 (pg/mL)
F: Adherent MNC TNF-? (pg/mL)
Control values are means of 4 (*), 2 (†) or 3 (‡) donors, with each donor showing significant increase as compared to unstimulated condition. Quantitation was by ELISA.
ND indicates not determined.
The Pediatric Infectious Disease Journal • Volume 27, Number 2, February 2008 Infections in IRAK-4 Deficiency
© 2008 Lippincott Williams & Wilkins
until 4.5 months of age, when she presented with right
preauricular and left submandibular masses, presumed to be
adenitis clinically, although relatively cold and nontender.
The patient was afebrile and had a normal WBC (13.1 ?
109/L) and neutrophil count (4.1 ? 109/L) with normal CRP
(?5 mg/L) and ESR (9 mm/h) but platelets were increased
(630 ? 109/L). S. aureus was isolated from purulent material
(including PMN) obtained by lymph-node aspiration. Re-
sponse to cloxacillin therapy for 10 days was poor, and
additional therapy with clindamycin and cefalexin was re-
quired for clinical resolution. The total antistaphylococcal
therapy was 26 days.
At 5 months, the patient presented with acute otitis
media but was again afebrile. Treatment with amoxicillin led
to rapid resolution without relapse. At 8 months, she was
hospitalized for a week with herpetic stomatitis. Treatment
with oral acyclovir and nystatin was effective.
At 12 months, after several months of failing to
thrive, a right submandibular mass developed. Presentation
was afebrile with normal WBC (11.3 ? 109/L), normal
CRP and ESR (9 mm/h) but elevated platelet count (636 ?
109/L). CT scan at this time revealed multiple submandib-
ular and cervical lymphadenitis and unsuspected paratra-
cheal lymphadenitis with mass effect. Only these areas
were visualized by gallium scan. Drainage and packing of
submandibular and paratracheal nodes was associated with
fever (39.3°C) and acute phase response (increased CRP
?40.7 mg/L? and ESR ?32 mm/h?) briefly 24 hours after
surgery. Response to prolonged antistaphylococcal therapy
was good with resolution of thrombocytosis and all lesions
on follow-up CT scans.
Immunologic evaluation indicated normal immuno-
globulins, and presence of normal amounts of specific IgG
antibodies except for low antipneumococcal polysaccharide
IgG. Complement activity, neutrophil NBT, splenic ultra-
sound, lymphocyte subpopulations, and lymphocyte prolifer-
ative response to antigens and mitogens were normal. The
IgG response to pneumococcal polysaccharides was weak
despite repeated immunization with pneumococcal-diphtheria
toxoid conjugate vaccine.
Diagnosis of IRAK-4 deficiency was suspected based
on clinical and routine laboratory findings and results of
blood leukocyte IL-6 production assay. The child’s DNA was
amplified and IRAK-4 gene was sequenced. Compound het-
erozygosity was determined with 1 allele containing a dele-
tion (631del_G) resulting in a premature stop codon at amino
acid 212. The other allele contained the point mutation
C144G, resulting in a tyrosine-to-stop-codon (Y48X) substi-
tution at position 48.
Since diagnosis in October 2005, the patient has been
well and is thriving while receiving prophylaxis with
cotrimoxazole and penicillin V, and repeated immuniza-
tion with pneumococcal and meningococcal conjugate vac-
MATERIALS AND METHODS
Whole-blood Cytokine Production. Anticoagulated whole
blood (10 U/mL sodium heparin) was collected from healthy
adult donors and from patients after informed consent in
accordance with the guidelines of the IWK Health Centre.
Blood was diluted as follows: 0.2 mL blood ? 0.6 mL
RPMI-1640 (endotoxin-free; Sigma Chemical Co., St. Louis,
MO) and cultured for 20 hours at 37°C in 5-mL polypro-
pylene tubes. The samples were either unstimulated, or stim-
ulated with IL-1? (Peprotech, Rocky Hill, NJ) at 50 ng/mL,
E. coli O111 lipopolysaccharide (LPS; List Biologicals,
Campbell, CA) at 10 ng/mL, S. aureus peptidoglycan (PGN;
Sigma Chemical Co.) at 30 ?g/mL or poly inosine-cytosine
(Poly I:C, PIC; Sigma Chemical Co.) at 30 ?g/mL. Super-
natants were harvested and cleared of cellular elements by
centrifugation (2000 g ? 10 minutes) and stored frozen until
Fresh adherent monocytes were prepared from heparin-
ized whole blood by separation on Ficoll-Paque Plus (GE
Healthcare Biosciences Inc., Baie d’Urfe ´, QC) and adherence to
24-well flat-bottom tissue culture plates for 2 hours. The adher-
ent monocytes (?95%) were washed to remove contaminating
cells and then stimulated in RPMI-10% fetal calf serum (Sigma
Chemical Co.) with the above stimuli for 20 hours as for whole
blood before harvesting the supernatants.
IL-6, IL-8 and TNF-? Assays. IL-6, IL-8, and TNF-? were
assayed using a sandwich ELISA method (R&D Systems, Min-
neapolis, MN) with low limit of detection in the range of 20–60
pg/mL, depending on the cytokine. Recombinant human IL-6,
IL-8, and TNF-? were used as standards (R&D Systems).
IRAK-4 Western Blotting on Fibroblasts. Human dermal
fibroblasts were grown from skin samples from patients and
controls with no immunologic condition. IRAK-4 protein was
detected by Western blotting technique using lysates from the
fibroblasts and probing the blots with rabbit antihuman
IRAK-4 antibody (eBioscience, San Diego, CA).
IRAK-4 Gene Sequencing. Genomic DNA from whole blood
cells or Epstein-Barr virus lymphoblastoid lines was isolated
and the IRAK-4 gene sequenced as previously described.12
Whole blood samples from both patients and healthy
control donors were stimulated with IL-1?, LPS, PGN, and PIC
for 20 hours. The concentrations of IL-6, TNF-?, and IL-8 in the
cell culture supernatants were then measured. Stimulation of
whole blood from control donors with the above stimuli resulted
in a dramatic increase in IL-6 production as compared with
unstimulated samples. In contrast, blood leukocytes from pa-
tients 1 and 2 showed no increase in IL-6 (Table 1A). When
adherent monocytes were stimulated with the same agents, the
monocytes from patient 2 showed no IL-6 response whereas
PIC but not to IL-1? (Table 1B).
Stimulation of whole blood from controls with IL-1?,
LPS, PGN, or PIC induced IL-8 production, with PGN inducing
the greatest response. In contrast with samples from patients 1
and 2, there was virtually no increase in IL-8 production with
IL-1?, LPS, or PIC (Table 1C). However, a considerable
amount of IL-8 was spontaneously produced (unstimulated) by
adherent monocytes of both controls and patients. The mono-
cytes of patient 1 had a weak response to LPS and PIC but none
Comeau et al
The Pediatric Infectious Disease Journal • Volume 27, Number 2, February 2008
© 2008 Lippincott Williams & Wilkins
to IL-1?, and patient 2 showed a small response (?3-fold) to
PIC only (Table 1D). In striking contrast, blood leukocytes and
adherent monocytes of both patients responded to PGN with an
increase in IL-8 production comparable to controls, despite the
fact that PGN failed to induce IL-6 production by the IRAK-4
deficient blood leukocytes.
Stimulation of whole blood or monocytes from control
donors resulted in an increase in TNF-? production as com-
pared with unstimulated samples. There was no increase in
TNF-? production with whole blood preparations from pa-
tient 1 upon IL-1?, LPS, or PIC stimulation, and only a very
weak response to PGN. As for IL-6 and IL-8, the adherent
monocytes of patient 1, but not patient 2, generated a weak
response to LPS and PIC for TNF-? production, despite a
complete lack of response to IL-1?. In contrast to the strong
response of blood leukocytes and adherent monocytes of the
patients to PGN for IL-8 production, the TNF-? response to
PGN was ?20% of controls if compared as fold increases
(Table 1E and 1F).
Western blot analysis was performed to probe for
IRAK-4 protein in primary dermal fibroblasts from patients 1
and 2 and control subjects (see online Supplementary Fig. 1).
No IRAK-4 protein of any size was detected in these cells
from either patient.
Although it has been previously reported that IRAK-4
deficiency may present with S. aureus4–6,8–10infection, to
our knowledge these are the first reports of bacterial pericar-
ditis, paratracheal abscesses, and peritonitis secondary to
In patient 1, pneumococcal meningitis occurred at 14
months. When he presented with irritability and fever, he had
normal WBC and relatively low CSF leukocytosis with nor-
mal CSF glucose and protein levels. This weak inflammatory
response in the CSF is consistent with other IRAK-4 deficient
patients who developed meningitis.7,8At age 9, when patient
1 was found to have hepatic abscesses by ultrasound, he had
only vague abdominal symptoms with no fever and without
elevated WBC. Similarly, patient 2, despite having multiple
lymphadenitis, was afebrile with a normal WBC, ESR, and
CRP before surgery.
In affected patients, it appears that the inflammatory
response is impaired, or fails to develop with localized
infection, and patients report little local tenderness with few
other physical symptoms. Even with bacteremia or bacterial
dissemination, acute phase responses may be absent or
muted. Thus, this immunodeficiency needs to be considered
in any patient where deep tissue bacterial infection and or
invasive infections such as meningitis, arthritis, and sepsis
occur without common constitutional symptoms (fever, local
pain, and inflammation) and/or lack or delay of acute phase
response. However, in some cases of longstanding infection,
even in IRAK-4 deficient patients the CRP may reach high
values,12therefore high acute phase responses, especially
after persistent vague symptoms, do not exclude IRAK-4
deficiency. Because of the silent infections, imaging of sus-
pected sites including contiguous draining lymphoid tissue
and possibly major reticuloendothelial system organs (eg,
liver, spleen) should be performed early. Gallium-67 scan or
indium-111 leukocyte scan may help to map the sites of
infection as was the case in patient 2 (not shown).
A presumptive diagnosis of IRAK-4 deficiency before
gene sequencing is possible by stimulating heparinized whole
blood with various microbial stimuli for IL-6 or TNF-?
production and demonstrating severely impaired responses,
particularly to IL-1? and LPS. Alternatively, a rapid screen-
ing test for IRAK-4 deficiency by flow cytometry was re-
cently reported, demonstrating failure of shedding of CD62L
(L-selectin) by IRAK-4 deficient blood PMN after stimula-
tion by TLR agonists.13
IL-6 and TNF-? are both inflammatory cytokines re-
sponsible for systemic signs of infection and inflammation
such as fever, acute phase responses, and inflammatory cell
recruitment.14,15IL-8 is a potent chemokine for PMN activa-
tion and migration to the site of infection or inflammation.16
In the IRAK-4 deficient patients, clinical presentation was
often afebrile, with lack of leukocytosis, or CRP elevation.
The frequent development of bacterial abscesses may be the
result of poor recruitment of inflammatory cells to fight
infection during the early phase as seen also by the weak
leukocyte response in the CSF to meningitis, as in patient 1
and observed previously.7,8,11Compounding the host defense
deficiency may be an impaired antibody response to polysac-
charide antigens,5including protein-polysaccharide-conju-
gated vaccines associated with low IgG2 subclass as observed
in our 2 patients.
Production of TNF-? and IL-8 in particular are crucial
for leukocyte recruitment and host defense.15–17Cytokine
production by whole blood reflects production by any of the
leukocyte types and may be influenced by immunoglobulins
and intact complement pathways, which are present and can
activate cells independent of TLR mechanisms. Therefore,
adherent monocytes (?95%) were also examined to mini-
mize these components. The stimuli selected were IL-1?,
LPS (a constituent of the outer membrane of Gram-negative
bacteria), S. aureus derived PGN (characteristic of Gram-
positive cell walls), and PIC, a mimic of viral RNA. IL-1?
activates through the IL-1 receptor, LPS is a TLR4 agonist,
PIC is a TLR3 agonist, and PGN is a TLR2 agonist and is
also recognized by other receptors.18The severely impaired
production of IL-6 or TNF-? in response to these stimuli in
both our patients is in keeping with the findings in other
IRAK-4 deficient patients. However, adherent monocytes of
patient 1 but not patient 2 mounted a small IL-6, IL-8, and
TNF-? response to LPS and PIC despite lack of any re-
sponses to these stimuli by whole-blood leukocytes or to
IL-1? by the monocytes. Thus there appears to be some
functional difference in the adherent monocytes in these
patients. Whether these differences are related to age (patient
1 was 15–16 years; patient 2, 1.5–2 years at the time of
testing) and/or alternative activation mechanisms in adherent
cells (eg, via TIR-domain-containing adapter-inducing inter-
feron ? [TRIF] pathway) is yet unclear.
In striking contrast, PGN induced a normal response for
IL-8 production in both whole blood and adherent mono-
cytes. PGN is known to be recognized by TLR2,18which
The Pediatric Infectious Disease Journal • Volume 27, Number 2, February 2008Infections in IRAK-4 Deficiency
© 2008 Lippincott Williams & Wilkins
initiates the IRAK-4 dependent activation of NF-?B. NOD is
an intracellular receptor that has also been shown to be
activated by PGN and to stimulate production of IL-8 and
TNF-?.19Other possible pathways through which PGN could
stimulate IL-8 production are through complement (eg, C3b,
C3a, 4a, 5a) or IgG-PGN complex binding to Fc receptors.
However, a normal PGN-induced IL-8 response was ob-
served also with adherent monocyte preparations where com-
plement was inactivated and immunoglobulin was virtually
absent (ie, in FCS). This may be because PGN is also
recognized by the intracellular receptors NOD1 and NOD2,
which also initiate NF-?B and MAPK activation, cytokine
production, and apoptosis.20,21In fact NOD1-dependent path-
ways can lead to IL-8 production via JNK activation and
RIP2, which activates the kinase TAK1 and bypasses the
The 4 mutations reported here have not been reported
previously. These mutations all eventually lead to a prema-
ture stop codon and this is consistent with the lack of IRAK-4
protein in either patients’ cells on Western blot analysis (see
online supplementary Fig. 1). To date at least 13 different
mutations have been described in the IRAK-4 genes of 28
different IRAK-4 deficient patients (Ku C.-L. et al, submit-
ted), and additional mutations are likely to be identified that
may have various consequences on the IRAK-4 protein,
perhaps with differing phenotypic presentations. Although
IRAK-4 deficiency can result in fatal infection (43% in a
recent series, Ku C.-L. et al, submitted for publication) or
infections which are silent and progress to major sequelae,
infections appear to be reasonably well controlled by prophy-
laxis with cotrimoxazole ? penicillin and repeated immuni-
zations with pneumococcal and other polysaccharide-protein
conjugate vaccines. The infectious consequences of IRAK-4
deficiency appear to diminish with age, especially beyond the
first decade, possibly because of improved adaptive immu-
nity, but the age beyond which antibiotic prophylaxis is no
longer necessary remains to be determined.
The authors are grateful to Mr D. Rowter and Ms F.
Liu for excellent technical assistance and to Ms A. Woolaver
for assistance with manuscript preparation. The authors also
wish to particularly thank Dr Peter Noonan of Charlotte-
town, Prince Edward Island, Canada for compiling important
clinical information on one of the patients.
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© 2008 Lippincott Williams & Wilkins