Inflammatory monocytes recruited to allergic skin acquire an anti-inflammatory M2 phenotype via basophil-derived interleukin-4.

Monocytes and macrophages are important effectors and regulators of inflammation, and both can be divided into distinct subsets based on their phenotypes. The developmental and functional relationship between individual subsets of monocytes and those of macrophages has not been fully elucidated, although Ly6C(+)CCR2(+) inflammatory and Ly6C(-)CCR2(-) resident monocytes are generally thought to differentiate into M1 (classically activated) and M2 (alternatively activated) macrophages, respectively. Here we show that inflammatory monocytes recruited to allergic skin acquired an M2-like phenotype in response to basophil-derived interleukin-4 (IL-4) and exerted an anti-inflammatory function. CCR2-deficient mice unexpectedly displayed an exacerbation rather than alleviation of allergic inflammation, in spite of impaired recruitment of inflammatory monocytes to skin lesions. Adoptive transfer of inflammatory monocytes from wild-type but not IL-4 receptor-deficient mice dampened the exacerbated inflammation in CCR2-deficient mice. Thus, inflammatory monocytes can be converted from being proinflammatory to anti-inflammatory under the influence of basophils in allergic reactions.

Hyper-IgE syndrome, 2021 update.

Clinically and pathologically, the patients with hyper-IgE syndrome present similar skin manifestations to common atopic dermatitis. The original hyper-IgE syndrome is characterized by diminished inflammatory response, in combination with Staphylococcus aureus skin abscess and pneumonia followed by pneumatocele formation. These immunological manifestations are frequently associated with skeletal and connective tissue abnormalities. We previously identified that major causal variants of the hyper-IgE syndrome are dominant negative variants in the STAT3. In addition to the identification of new causative variants for the disorders similar to the original hyper-IgE syndrome, causative variants for new types of hyper-IgE syndrome centered only on atopy, high serum IgE levels, and susceptibility to infection, but not associated with diminished inflammatory response, pneumatocele formation, and connective tissue manifestations, have been identified. Recent discovery identified a novel zinc finger protein that regulates STAT3 transcription. Investigation of IL6ST variants disclosed that IL6ST/IL6R cytokine receptor plays a crucial role for the signal transduction upstream of STAT3 in the pathogenesis of the original hyper-IgE syndrome. Even if the same IL6ST variants are used for the signal transduction of IL-6 family cytokines, the signaling defect is more severe in IL-6/IL-11 and milder in LIF. The fact that the non-immune manifestations of the gain-of-function mutations of TGFBR1 and TGFBR2 are similar to the those of dominant negative mutations of STAT3 provide a clue to elucidate molecular mechanisms of non-immune manifestations of hyper-IgE syndrome. Research on this hereditary atopic syndrome is being actively conducted to elucidate the molecular mechanisms and to develop new therapeutic approaches.

The C-terminal region including the MH6 domain of Msx1 regulates skeletal development.

MSX1 is a causative gene for oligodontia in humans. Although conventional Msx1-deficient mice die neonatally, a mutant mouse lacking the C-terminus MH6 domain of MSX1 (Msx1ΔMH6/ΔMH6) showed two different phenotypes; newborn homozygotes with cleft palates died neonatally, whereas those with thin palates remained alive and had craniofacial dysplasia and growth retardation compared with wild-type mice, with most mice dying by the age of 4-5 weeks. In a previously reported case of human oligodontia caused by a heterozygous defect of the Msx1 MH6 domain, a small foramen was observed on the occipital bone. The aim of this study was to test the hypothesis that the Msx1 MH6 domain is involved in bone formation in vivo. In Msx1ΔMH6/ΔMH6 mice, cranial suture fusion was delayed at embryonic day 18.5, and the anteroposterior cranial diameter was smaller and long bone length was decreased at 3 weeks of age. The femoral epiphysis showed no change in the trabecular number, but decreased bone mass, bone density, and trabecular width in Msx1ΔMH6/ΔMH6 mice. In addition, cancellous bone mass was reduced and the cartilage layer in the growth plate was thinner in Msx1ΔMH6/ΔMH6 mice. The mRNA expression levels of major osteoblast and chondrocyte differentiation marker genes were decreased in Msx1ΔMH6/ΔMH6 mice compared with wild-type mice. These findings suggest that the C-terminal region including the MH6 domain of MSX1 plays important roles not only in tooth development and palatal fusion, but also in postnatal bone formation.

Basophils play a pivotal role in immunoglobulin-G-mediated but not immunoglobulin-E-mediated systemic anaphylaxis.

Anaphylaxis is an acute, severe, and potentially fatal systemic allergic reaction. Immunoglobulin E (IgE), mast cells, and histamine have long been associated with anaphylaxis, but an alternative pathway mediated by IgG has been suggested to be more important in the elicitation of anaphylaxis. Here, we showed that basophils, the least common blood cells, were dispensable for IgE-mediated anaphylaxis but played a critical role in IgG-mediated, passive and active systemic anaphylaxis in mice. In vivo depletion of basophils but not macrophages, neutrophils, or NK cells ameliorated IgG-mediated passive anaphylaxis and rescued mice from death in active anaphylaxis. Upon capture of IgG-allergen complexes, basophils released platelet-activating factor (PAF), leading to increased vascular permeability. These results highlight a pivotal role for basophils in vivo and contrast two major, distinct pathways leading to allergen-induced systemic anaphylaxis: one mediated by basophils, IgG, and PAF and the other "classical" pathway mediated by mast cells, IgE, and histamine.

Monogenic mutations differentially affect the quantity and quality of T follicular helper cells in patients with human primary immunodeficiencies.

BACKGROUND: Follicular helper T (TFH) cells underpin T cell-dependent humoral immunity and the success of most vaccines. TFH cells also contribute to human immune disorders, such as autoimmunity, immunodeficiency, and malignancy. Understanding the molecular requirements for the generation and function of TFH cells will provide strategies for targeting these cells to modulate their behavior in the setting of these immunologic abnormalities. OBJECTIVE: We sought to determine the signaling pathways and cellular interactions required for the development and function of TFH cells in human subjects. METHODS: Human primary immunodeficiencies (PIDs) resulting from monogenic mutations provide a unique opportunity to assess the requirement for particular molecules in regulating human lymphocyte function. Circulating follicular helper T (cTFH) cell subsets, memory B cells, and serum immunoglobulin levels were quantified and functionally assessed in healthy control subjects, as well as in patients with PIDs resulting from mutations in STAT3, STAT1, TYK2, IL21, IL21R, IL10R, IFNGR1/2, IL12RB1, CD40LG, NEMO, ICOS, or BTK. RESULTS: Loss-of-function (LOF) mutations in STAT3, IL10R, CD40LG, NEMO, ICOS, or BTK reduced cTFH cell frequencies. STAT3 and IL21/R LOF and STAT1 gain-of-function mutations skewed cTFH cell differentiation toward a phenotype characterized by overexpression of IFN-γ and programmed death 1. IFN-γ inhibited cTFH cell function in vitro and in vivo, as corroborated by hypergammaglobulinemia in patients with IFNGR1/2, STAT1, and IL12RB1 LOF mutations. CONCLUSION: Specific mutations affect the quantity and quality of cTFH cells, highlighting the need to assess TFH cells in patients by using multiple criteria, including phenotype and function. Furthermore, IFN-γ functions in vivo to restrain TFH cell-induced B-cell differentiation. These findings shed new light on TFH cell biology and the integrated signaling pathways required for their generation, maintenance, and effector function and explain the compromised humoral immunity seen in patients with some PIDs.

Functional STAT3 deficiency compromises the generation of human T follicular helper cells.

T follicular helper (Tfh) cells are critical for providing the necessary signals to induce differentiation of B cells into memory and Ab-secreting cells. Accordingly, it is important to identify the molecular requirements for Tfh cell development and function. We previously found that IL-12 mediates the differentiation of human CD4(+) T cells to the Tfh lineage, because IL-12 induces naive human CD4(+) T cells to acquire expression of IL-21, BCL6, ICOS, and CXCR5, which typify Tfh cells. We have now examined CD4(+) T cells from patients deficient in IL-12Rß1, TYK2, STAT1, and STAT3 to further explore the pathways involved in human Tfh cell differentiation. Although STAT1 was dispensable, mutations in IL12RB1, TYK2, or STAT3 compromised IL-12-induced expression of IL-21 by human CD4(+) T cells. Defective expression of IL-21 by STAT3-deficient CD4(+) T cells resulted in diminished B-cell helper activity in vitro. Importantly, mutations in STAT3, but not IL12RB1 or TYK2, also reduced Tfh cell generation in vivo, evidenced by decreased circulating CD4(+)CXCR5(+) T cells. These results highlight the nonredundant role of STAT3 in human Tfh cell differentiation and suggest that defective Tfh cell development and/or function contributes to the humoral defects observed in STAT3-deficient patients.

NK cell-depleting anti-asialo GM1 antibody exhibits a lethal off-target effect on basophils in vivo.

NK cells are innate immune lymphocytes and play a key role in both innate and adaptive immunity. Their pivotal functions in vivo have been illustrated in mice by means of their ablation with NK cell-depleting Abs, particularly anti-asialo GM1 (ASGM1). In this study, we show that the whole population of basophils constitutively expresses ASGM1 as well as CD49b (DX5) as does the NK cell population and was ablated in vivo by anti-ASGM1 as efficiently as by a basophil-depleting anti-FcεRIα Ab. Anti-ASGM1-mediated basophil depletion was operative as for NK cell depletion in various mouse strains, irrespective of NK1 allotype and MHC H2 haplotype, including C57BL/6, BALB/c, C3H, and A/J mice. These results identified basophils as a previously unrecognized target of anti-ASGM1-mediated cell depletion and raised concern about possible contribution of basophils, rather than or in addition to NK cells, to some of phenotypes observed in anti-ASGM1-treated mice. Indeed, regardless of the presence or absence of NK cells in mice, anti-ASGM1 treatment abolished the development of IgE-mediated chronic cutaneous allergic inflammation as efficiently as did the treatment with basophil-depleting Ab. Given the fact that basophils have recently been shown to play crucial roles in a variety of immune responses, our finding of the off-target effect on basophils issues a grave warning about the use of anti-ASGM1 and underscores the need for careful interpretation of phenotypes observed in anti-ASGM1-treated mice.

Dominant-negative mutations in the DNA-binding domain of STAT3 cause hyper-IgE syndrome.

Hyper-immunoglobulin E syndrome (HIES) is a compound primary immunodeficiency characterized by a highly elevated serum IgE, recurrent staphylococcal skin abscesses and cyst-forming pneumonia, with disproportionately milder inflammatory responses, referred to as cold abscesses, and skeletal abnormalities. Although some cases of familial HIES with autosomal dominant or recessive inheritance have been reported, most cases of HIES are sporadic, and their pathogenesis has remained mysterious for a long time. Here we show that dominant-negative mutations in the human signal transducer and activator of transcription 3 (STAT3) gene result in the classical multisystem HIES. We found that eight out of fifteen unrelated non-familial HIES patients had heterozygous STAT3 mutations, but their parents and siblings did not have the mutant STAT3 alleles, suggesting that these were de novo mutations. Five different mutations were found, all of which were located in the STAT3 DNA-binding domain. The patients' peripheral blood cells showed defective responses to cytokines, including interleukin (IL)-6 and IL-10, and the DNA-binding ability of STAT3 in these cells was greatly diminished. All five mutants were non-functional by themselves and showed dominant-negative effects when co-expressed with wild-type STAT3. These results highlight the multiple roles played by STAT3 in humans, and underline the critical involvement of multiple cytokine pathways in the pathogenesis of HIES.

The signal transducer and activator of transcription 3 at the center of the causative gene network of the hyper-IgE syndrome.

The hyper-IgE syndrome (HIES) is characterized by atopic dermatitis with extremely high serum IgE levels and diminished inflammatory responses, in combination with bacterial and fungal infections followed by pneumatocele formation. These immunological manifestations are frequently associated with nonimmunological abnormalities, including characteristic face, pathological fracture, and retention of deciduous teeth. We previously identified that major causal variants of the HIES are dominant-negative variants in the signal transducer and activator of transcription 3 (STAT3) gene. Several new causative variants of HIES have been identified, interestingly, most of which are functionally associated with STAT3. These include a zinc finger transcription factor ZNF341 as well as IL-6 family cytokine receptors, IL6ST, and IL-6R. In this review, I will outline the pathological mechanisms of new causative variants, in which STAT3 is at the center of the causative gene network.

Effects of Wnt10a and Wnt10b Double Mutations on Tooth Development.

WNT molecules are the regulators of various biological functions, including body axis formation, organ development, and cell proliferation and differentiation. WNTs have been extensively studied as causative genes for an array of diseases. WNT10A and WNT10B, which are considered to be genes of the same origin, have been identified as causative genes for tooth deficiency in humans. However, the disrupted mutant of each gene does not show a decrease in teeth number. A negative feedback loop, interacting with several ligands based on a reaction-diffusion mechanism, was proposed to be important for the spatial patterning of tooth formation, and WNT ligands have been considered to play a pivotal role in controlling tooth patterning from mutant phenotypes of LDL receptor-related proteins (LRPs) and WNT co-receptors. The Wnt10a and Wnt10b double-mutants demonstrated severe root or enamel hypoplasia. In Wnt10a-/- and Wnt10a+/-;Wnt10b-/- mice, changes in the feedback loop may collapse the modulation of fusion or split a sequence of tooth formation. However, in the double-knockout mutant, a decrease in the number of teeth was observed, including the upper incisor or third molar in both jaws. These findings suggest that there may be a functional redundancy between Wnt10a and Wnt10b and that the interaction between the two genes functions in conjunction with other ligands to control the spatial patterning and development of teeth.

Successful treatment of DOCK8 deficiency by allogeneic hematopoietic cell transplantation from alternative donors.

Dedicator of cytokinesis 8 (DOCK8) deficiency is a rare autosomal recessive inborn error of immunity (IEI) characterized by eczematous dermatitis, elevated serum IgE, and recurrent infections, comprising a seemingly hyper-IgE syndrome (HIES). DOCK8 deficiency is only curable with allogeneic hematopoietic cell transplantation (HCT), but the outcome of HCT from alternative donors is not fully understood. Here, we describe the cases of two Japanese patients with DOCK8 deficiency who were successfully treated by allogeneic HCT from alternative donors. Patient 1 underwent cord blood transplantation at the age of 16 years, and Patient 2 underwent haploidentical peripheral blood stem cell transplantation with post-transplant cyclophosphamide at the age of 22 years. Each patient received a fludarabine-based conditioning regimen. Their clinical manifestations, including refractory molluscum contagiosum, promptly improved post-HCT. They achieved successful engraftment and immune reconstitution without serious complications. Alternative donor sources such as cord blood and haploidentical donors can be options for allogeneic HCT for DOCK8 deficiency.

Th2-inducing cytokines IL-4 and IL-33 synergistically elicit the expression of transmembrane TNF-α on macrophages through the autocrine action of IL-6.

Tumor necrosis factor-α (TNF-α) is a potent proinflammatory cytokine produced predominantly by activated macrophages, and plays a central role in the protective immunity against intracellular pathogens and the pathogenesis of autoimmune and inflammatory diseases. While both the soluble and transmembrane forms of TNF-α (sTNF-α and tmTNF-α) are biologically functional, the latter but not the former acts as a receptor besides as a ligand, and transmit a retrograde signal in a cell-to-cell contact manner. The production of TNF-α by macrophages under Th2-type (allergic) inflammatory conditions has been ill defined, compared to that under Th1-type inflammatory conditions. Here we examined the effect of representative Th2-inducing cytokines IL-4 and IL-33 on the TNF-α expression in macrophages. IL-4 induced the production of neither sTNF-α nor tmTNF-α while IL-33 promoted the production of sTNF-α with no detectable tmTNF-α. Notably, the combination of IL-4 and IL-33 elicited the tmTNF-α expression on macrophages, in addition to the enhanced production of sTNF-α and IL-6. The IL-4/IL-33-elicited tmTNF-α expression was not observed in IL-6-deficient macrophages, suggesting the involvement of macrophage-derived IL-6 in the tmTNF-α expression. Indeed, the stimulation of macrophages with the combination of IL-4 and IL-6 induced the tmTNF-α expression with no detectable production of sTNF-α. Thus, IL-4 and IL-33 synergistically elicit the tmTNF-α expression on macrophages through the autocrine action of IL-6.

An atopic dermatitis-like skin disease with hyper-IgE-emia develops in mice carrying a spontaneous recessive point mutation in the Traf3ip2 (Act1/CIKS) gene.

Spontaneous mutant mice that showed high levels of serum IgE and an atopic dermatitis (AD)-like skin disease were found in a colony of the KOR inbred strain that was derived from Japanese wild mice. No segregation was observed between hyper-IgE-emia and dermatitis in (BALB/c x KOR mutant) N(2) mice, suggesting that the mutation can be attributed to a single recessive locus, which we designated adjm (atopic dermatitis from Japanese mice). All four adjm congenic strains in different genetic backgrounds showed both hyper-IgE-emia and dermatitis, although the disease severity varied among strains. Linkage analysis using (BALB/c x KOR-adjm/adjm) N(2) mice restricted the potential adjm locus to the 940 kb between D10Stm216 and D10Stm238 on chromosome 10. Sequence analysis of genes located in this region revealed that the gene AI429613, which encodes the mouse homologue of the human TNFR-associated factor 3-interacting protein 2 (TRAF3IP2) protein (formerly known as NF-kappaB activator 1/connection to IkappaB kinase and stress-activated protein kinase/Jun kinase), carried a single point mutation leading to the substitution of a stop codon for glutamine at amino acid position 214. TRAF3IP2 has been shown to function as an adaptor protein in signaling pathways mediated by the TNFR superfamily members CD40 and B cell-activating factor in epithelial cells and B cells as well as in the IL-17-mediated signaling pathway. Our results suggest that malfunction of the TRAF3IP2 protein causes hyper-IgE-emia through the CD40- and B cell-activating factor-mediated pathway in B cells and causes skin inflammation through the IL-17-mediated pathway. This study demonstrates that the TRAF3IP2 protein plays an important role in AD and suggests the protein as a therapeutic target to treat AD.

Cutaneous manifestations of Hyper IgE syndrome.

Hyper-IgE syndrome (HIES) is a primary immunodeficiency disorder characterized by atopic manifestations and susceptibility to infections with extracellular bacteria and fungi. Atopic manifestations include atopic dermatitis-like skin lesion and extremely high serum IgE levels. Most of the extracellular bacterial infections are caused by Staphylococcus aureus, which is associated with milder inflammation compared to normal. Recent studies have revealed that the most cases of the HIES are caused by dominant negative mutations in STAT3 gene. Cutaneous manifestations of HIES includes newborn rash, eczematoid dermatitis, cold abscesses, mucocutaneous candidiasis, and coarse texture of the facial skin. Impaired Th17 cell development due to the defective IL-6 signaling in T cells and impaired induced regulatory T (iTreg) cell generation due to defective IL-10 signaling in dendritic cells may, at least in part, account for the cutaneous pathology of HIES.

Impaired IL-23-dependent induction of IFN-γ underlies mycobacterial disease in patients with inherited TYK2 deficiency.

Human cells homozygous for rare loss-of-expression (LOE) TYK2 alleles have impaired, but not abolished, cellular responses to IFN-α/ß (underlying viral diseases in the patients) and to IL-12 and IL-23 (underlying mycobacterial diseases). Cells homozygous for the common P1104A TYK2 allele have selectively impaired responses to IL-23 (underlying isolated mycobacterial disease). We report three new forms of TYK2 deficiency in six patients from five families homozygous for rare TYK2 alleles (R864C, G996R, G634E, or G1010D) or compound heterozygous for P1104A and a rare allele (A928V). All these missense alleles encode detectable proteins. The R864C and G1010D alleles are hypomorphic and loss-of-function (LOF), respectively, across signaling pathways. By contrast, hypomorphic G996R, G634E, and A928V mutations selectively impair responses to IL-23, like P1104A. Impairment of the IL-23-dependent induction of IFN-γ is the only mechanism of mycobacterial disease common to patients with complete TYK2 deficiency with or without TYK2 expression, partial TYK2 deficiency across signaling pathways, or rare or common partial TYK2 deficiency specific for IL-23 signaling.

Basophil-derived mouse mast cell protease 11 induces microvascular leakage and tissue edema in a mast cell-independent manner.

Mouse mast cell protease 11 (mMCP-11) is the most recently identified member of the mouse mast cell tryptase family. This tryptase is preferentially produced by basophils in contrast to other members that are expressed by mast cells but not basophils. Although blood-circulating basophils have long been considered as minor and redundant relatives of tissue-resident mast cells, recent studies illustrated that basophils and mast cells play distinct roles in vivo. To explore the in vivo role of basophil-derived mMCP-11, here we prepared recombinant mMCP-11 and its protease-dead mutant. Subcutaneous injection of the wild-type mMCP-11 but not the mutant induced edematous skin swelling with increased microvascular permeability in a dose-dependent manner. No apparent infiltration of proinflammatory cells including neutrophils and eosinophils was detected in the skin lesions. The cutaneous swelling was abolished by the pretreatment of mice with indomethacin, a cyclooxygenase inhibitor, suggesting the major contribution of prostaglandins to the microvascular leakage. Of note, the cutaneous swelling was elicited even in mast cell-deficient mice, indicating that mast cells are dispensable for the mMCP-11-induced cutaneous swelling. Thus, basophil-derived mMCP-11 can induce microvascular leakage via prostaglandins in a mast cell-independent manner, and may contribute to the development of basophil-mediated inflammatory responses.

IgG-mediated systemic anaphylaxis to protein antigen can be induced even under conditions of limited amounts of antibody and antigen.

Systemic anaphylaxis is an acute, severe, and potentially fatal allergic reaction. Two classes of antibodies, IgE and IgG, contribute to the development of anaphylaxis in mice, through different mechanisms with distinct usage of effector cells and chemical mediators. Larger quantities of antibody and antigen are reportedly required to induce IgG-mediated anaphylaxis than IgE-mediated one, suggesting that the former may not happen as frequently as the latter in real life. To readdress this issue, we established in the present study a novel mouse model of passive IgG-mediated systemic anaphylaxis to a native protein antigen, ovalbumin (OVA), rather than artificially haptenated protein antigens used in previous studies. Passive sensitization of mice with a cocktail of but not individual IgG1 mAbs specific to distinct OVA epitopes elicited systemic anaphylaxis in response to OVA challenge. Importantly, much smaller doses of antibody and antigen than previously reported were sufficient for the induction of IgG-mediated systemic anaphylaxis. Moreover, a relatively small dose of antigen could induce severe anaphylaxis through both IgE- and IgG-mediated mechanisms when mice had been passively sensitized with antigen-specific IgE and IgG. These results strongly suggest that IgG-mediated systemic anaphylaxis is not rare among antibody-mediated systemic anaphylaxis, in contrast to previous thought, and significantly contributes to active systemic anaphylaxis in real life, at least in mice.

Defects in Jak-STAT-mediated cytokine signals cause hyper-IgE syndrome: lessons from a primary immunodeficiency.

Hyper-IgE syndrome (HIES) is a primary immunodeficiency characterized by atopic manifestations and susceptibility to infections with extracellular bacteria and fungi, which frequently occur in the skin and lung. Atopic manifestations in HIES include extremely high serum IgE levels, eczema and eosinophilia. Most of the extracellular bacterial infections are associated with disproportionally milder inflammation than normal, which was originally described as having a 'cold abscess'. Non-immunological abnormalities are also observed in most patients with HIES, including a distinctive facial appearance, scoliosis, hyper-extensive joints and retained primary teeth. Recent studies have demonstrated that hypomorphic mutations in signal transducer and activator of transcription 3 result in the classical multisystem form of HIES, whereas a null mutation in tyrosine kinase 2 causes the autosomal recessive form of HIES that is associated with viral and mycobacterial infections. Analyses of cytokine responses in both types of HIES have revealed defects in signal transduction for multiple cytokines including IL-6 and IL-23, leading to impaired T(h)17 function. These results suggest that the defect in multiple cytokine signals is the molecular basis of the immunological and non-immunological abnormalities in HIES and that the susceptibility to infections with extracellular bacteria and fungi in HIES might be associated with the defect in T(h)17 cell differentiation.

The skewed heavy-chain repertoire in peritoneal B-1 cells is predetermined by the selection via pre-B cell receptor during B cell ontogeny in the fetal liver.

As many as 5-15% of B-1 cells in the peritoneal cavity of adult mice produce antibodies reactive to phosphatidylcholine (PtC) and the vast majority of them express B cell receptors (BCRs) composed of V(H)11-muH chains utilizing the J(H)1 segment and Vkappa9-L chains. This extremely skewed repertoire of PtC-reactive B-1 cells is traditionally attributed to the expansion of particular clones in response to self or exogenous antigens. Here, we show that the strong bias toward the J(H)1 usage among V(H)11-muH chains is already established prior to the BCR assembly, namely at the transition from the large to the small pre-B cell stage during B cell ontogeny in the fetal liver. Among V(H)11-muH clones isolated from large pre-B cells where the J(H)1 skewing was not established yet, the J(H)1 users showed the highest ability to form pre-B cell receptor (pre-BCR) and to induce cellular proliferation and differentiation when expressed in fetal liver pro-B cells. Thus, the J(H)1 users were positively selected and amplified at the pre-BCR checkpoint. When co-expressed with Vkappa9-L chains to form BCR, the J(H)1 users almost exclusively conferred the PtC reactivity on BCR even though other J(H) users could also form BCR on the cell surface. Therefore, the pre-BCR-mediated positive selection of the J(H)1 users among V(H)11-muH chains appears to be beneficial to the efficient generation of 'innate-type' PtC-reactive B cells during the fetal B cell development, even before the self-renewal or the antigen-driven clonal expansion of B-1 cells takes place in the peritoneal cavity.

Genetic origins of hyper-IgE syndrome.

Hyper-IgE syndrome (HIES) is a complex primary immunodeficiency characterized by high serum IgE, chronic eczematoid dermatitis, and recurrent extracellular bacterial infections. Two types of HIES have been reported: type 1 and type 2. Type 1 HIES displays abnormalities in multiple systems, including the skeletal, dental, and immune systems, whereas type 2 shows abnormalities confined to the immune system. We recently identified hypomorphic mutations in the signal transducer and activator of transcription 3 (STAT3) gene in type 1 HIES and a null mutation in the tyrosine kinase 2 (Tyk2) gene, accompanied by susceptibility to intracellular bacteria in type 2 HIES. Analyses of cytokine responses in both types of HIES revealed that severe defects in the signal transduction for multiple cytokines, including interleukin-6 and interleukin-23, are leading to impaired T-helper type 17 function. These findings suggest that HIES is caused by the defects in multiple cytokine signals and that the susceptibility to various infections in HIES is associated with the T-helper type 17 defect.