Hyperimmunoglobulin E syndrome and tyrosine kinase 2 deficiency

STAT3-Specific Single Domain Nanobody Inhibits Expansion of Pathogenic Th17 Responses and Suppresses Uveitis in Mice

STAT3 activates transcription of genes that regulate cell growth, differentiation, and survival of mammalian cells. Genetic deletion of Stat3 in T cells has been shown to abrogate Th17 differentiation, suggesting that STAT3 is a potential therapeutic target for Th17-mediated diseases. However, a major impediment to therapeutic targeting of intracellular proteins such as STAT3 is the lack of efficient methods for delivering STAT3 inhibitors into cells. In this study, we developed a novel antibody (SBT-100) comprised of the variable (V) region of a STAT3-specific heavy chain molecule and demonstrate that this 15 kDa STAT3-specific nanobody enters human and mouse cells, and induced suppression of STAT3 activation and lymphocyte proliferation in a concentration-dependent manner. To investigate whether SBT-100 would be effective in suppressing inflammation in vivo, we induced experimental autoimmune uveitis (EAU) in C57BL/6J mice by active immunization with peptide from the ocular autoantigen, interphotoreceptor retinoid binding protein (IRBP_651-670). Analysis of the retina by fundoscopy, histological examination, or optical coherence tomography showed that treatment of the mice with SBT-100 suppressed uveitis by inhibiting expansion of pathogenic Th17 cells that mediate EAU. Electroretinographic (ERG) recordings of dark and light adapted a- and b-waves showed that SBT-100 treatment rescued mice from developing significant visual impairment observed in untreated EAU mice. Adoptive transfer of activated IRBP-specific T cells from untreated EAU mice induced EAU, while EAU was significantly attenuated in mice that received IRBP-specific T cells from SBT-100 treated mice. Taken together, these results demonstrate efficacy of SBT-100 in mice and suggests its therapeutic potential for human autoimmune diseases.

Staphylococcus aureus and Hyper-IgE Syndrome

Hyper-immunoglobulin E syndrome (HIES) is a primary immunodeficiency disease characterized by recurrent Staphylococcus aureus (S. aureus) infections, eczema, skeletal abnormalities and high titers of serum immunoglobulin E. Although the genetic basis of HIES was not known for almost a half century, HIES most frequently exhibits autosomal dominant trait that is transmitted with variable expressivity. Careful genetic studies in recent years identified dominant-negative mutations in human signal transducer and activator of transcription 3 (STAT3) gene as the cause of sporadic and dominant forms of HIES. The STAT3 mutations were localized to DNA-binding, SRC homology 2 (SH2) and transactivating domains and disrupted T helper 17 (T_H17) cell differentiation and downstream expression of T_H17 cytokines IL-17 and IL-22. Deficiency of IL-17 and IL-22 in turn is responsible for suboptimal expression of anti-staphylococcal host factors, such as neutrophil-recruiting chemokines and antimicrobial peptides, by human keratinocytes and bronchial epithelial cells. T_H17 cytokines deficiency thereby explains the recurrent staphylococcal lung and skin infections of HIES patients.

A TYK2 Gene Mutation c.2395G>A Leads to TYK2 Deficiency: A Case Report and Literature Review

Tyrosine kinase 2 (TYK2) deficiency was formerly defined in patients suffering from autosomal recessive hyperimmunoglobulin E syndrome (AR-HIES). In recent years, it was proposed that human TYK2 deficiency is probably not a common cause of the AR-HIES but a distinctive illness object. In the current work, a recessive TYK2 deficiency is reported in a patient suffering from BCG disease and recurrent respiratory infection. It was implied that this patient carried novel missense homozygous mutation (c.2395G>A, p. G799R) in the TYK2. Both the in vivo and in vitro experiments indicated the inhibition effects of the c.2395G>A homozygous mutation on the TYK2 gene and protein expression. By literature review, we summarized the clinical manifestations, gene mutations, and related cytokine responses of formerly reported patients possessing TYK2 deficiency. The core manifestation of these patients is infected by intracellular pathogens, such as mycobacteria and/or viruses. Therefore, the possibility of TYK2 deficiency should be considered when a patient has repeated intracellular bacteria (including tuberculosis bacillus infection), repeated viral infection or eczema.

Humoral immunodeficiencies: conferred risk of infections and benefits of immunoglobulin replacement therapy

Primary immunodeficiency (PID) diseases result from genetic defects of the immune system that increase a patient's susceptibility to infections. The types of infections that occur in patients with PID diseases are dictated largely by the nature of the immunodeficiency, which can be defined by dysfunction of cellular or humoral defenses. An increasing number of PID diseases, including those with both cellular and humoral defects, have antibody deficiency as a major feature, and as a result can benefit from immunoglobulin replacement therapy. In fact, the most common PID diseases worldwide are antibody deficiencies and include common variable immunodeficiency, congenital agammaglobulinemia, hyper‐IgM syndrome, specific antibody deficiency, and Good syndrome. Although immunoglobulin replacement therapy is the cornerstone of treatment for the majority of these conditions, a thorough understanding of the specific infections for which these patients are at increased risk can hasten diagnosis and guide additional therapies. Moreover, the infection trends in some patients with PID disease who have profound defects of cellular immunity, such as autosomal‐dominant hyper‐IgE syndrome (Job/Buckley syndrome) or dedicator of cytokinesis 8 (DOCK8) deficiency, suggest that select patients might benefit from immunoglobulin replacement therapy even if their immunodeficiency is not limited to antibody defects. In this review, we provide an overview of the predisposition to infections seen in PID disease that may benefit from immunoglobulin replacement therapy.

Approach to a Child with Primary Immunodeficiency Made Simple

Primary immunodeficiency disorders (PIDs) are a group of disorders affecting the capability to fight against infection. These include defects in T cells and B cells affecting cell-mediated and humoral immunity, respectively, combined humoral and cell-mediated immunodeficiency, defects in phagocytosis, complement defects, and defects in cytokine or cytokine signalling pathways which are detrimental for immune function. Depending upon the type and severity, age at onset of symptoms can vary from neonatal period to late childhood. Clinically, this group of disorders can involve any organ system of an individual such as respiratory system, gastrointestinal system, skin and mucous membrane, bone and joints, endocrine organs, and nervous system. Common dermatological manifestations include eczema, warts, molluscum contagiosum, mucocutaneous candidiasis, recurrent nonhealing ulcers, skin abscesses, erythroderma, petechiae, and nail changes. The common skin manifestations of various PIDs include eczema (seen in Wiskott-Aldrich syndrome and autosomal dominant hyper IgE syndrome); erythroderma (in Omen syndrome); viral warts or molluscum contagiosum (in autosomal recessive hyper IgE syndrome); chronic mucocutaneous candidiasis (in hyper IgE syndrome, autoimmune polyendocrinopathy candidiasis ectodermal dysplasia syndrome, Th17 cell defects); recurrent nonhealing ulcers (in leucocyte adhesion defect); skin abscesses (in antibody defects, hyper IgE syndrome, and chronic granulomatous disease); petechial or purpuric spots (in Wiskott-Aldrich syndrome).

Primary immunodeficiency update: Part I. Syndromes associated with eczematous dermatitis

In the past decade, the availability of powerful molecular techniques has accelerated the pace of discovery of several new primary immunodeficiencies (PIDs) and revealed the biologic basis of other established PIDs. These genetic advances, in turn, have facilitated more precise phenotyping of associated skin and systemic manifestations and provide a unique opportunity to better understand the complex human immunologic response. These continuing medical education articles will provide an update of recent advances in PIDs that may be encountered by dermatologists through their association with eczematous dermatitis, infectious, and non-infectious cutaneous manifestations. Part I will discuss new primary immunodeficiencies that have an eczematous dermatitis. Part II will focus on primary immunodeficiencies that greatly increase susceptibility to fungal infection and the noninfectious presentations of PIDs.

A Genetic-Pathophysiological Framework for Craniosynostosis

Craniosynostosis, the premature fusion of one or more cranial sutures of the skull, provides a paradigm for investigating the interplay of genetic and environmental factors leading to malformation. Over the past 20 years molecular genetic techniques have provided a new approach to dissect the underlying causes; success has mostly come from investigation of clinical samples, and recent advances in high-throughput DNA sequencing have dramatically enhanced the study of the human as the preferred "model organism." In parallel, however, we need a pathogenetic classification to describe the pathways and processes that lead to cranial suture fusion. Given the prenatal onset of most craniosynostosis, investigation of mechanisms requires more conventional model organisms; principally the mouse, because of similarities in cranial suture development. We present a framework for classifying genetic causes of craniosynostosis based on current understanding of cranial suture biology and molecular and developmental pathogenesis. Of note, few pathologies result from complete loss of gene function. Instead, biochemical mechanisms involving haploinsufficiency, dominant gain-of-function and recessive hypomorphic mutations, and an unusual X-linked cellular interference process have all been implicated. Although few of the genes involved could have been predicted based on expression patterns alone (because the genes play much wider roles in embryonic development or cellular homeostasis), we argue that they fit into a limited number of functional modules active at different stages of cranial suture development. This provides a useful approach both when defining the potential role of new candidate genes in craniosynostosis and, potentially, for devising pharmacological approaches to therapy.

Fifty-five-year-old man with chronic yeast infections

As immunologists, we are frequently asked to evaluate patients with recurrent infections. These infections can provide us with clues regarding what pathways might be aberrant in a given patient, e.g., specific pyogenic bacteria with Toll-like receptor problems, atypical mycobacteria with interferon gamma receptor autoantibodies, and Candida/staphylococcal infections with cellular immune abnormalities. We present a 55-year-old man who presented to our immunology clinic with onychodystrophy of the toenails and fingernails and recurrent oral-esophageal candidiasis. The differential diagnosis for recurrent yeast infections is complex and includes usual suspects as well as some that are not as straightforward.

The Hyperimmunoglobulinemia E Syndromes: A Literature Review

The hyper-immunoglobulin E (IgE) syndromes (HIES) are primary immunodeficiencies characterized by the recurrent staphylococcal abscesses, recurrent pneumonia and highly elevated serum IgE levels. There are two forms of HIES: a dominant form (AD-HIES) and a recessive form (AR-HIES). AD form of HIES is caused by mutations in STAT3 and the AR form is caused by mutations in DOCK8 and TYK2. These syndromes have different clinical presentations and outcomes. AD-HIES is a multisystem disorder that includes abnormalities of the skin, lungs, musculo-skeletal system and dental system. In contrast, these symptoms in patients with AR-HIES are missing. AR-HIES patients have severe viral infections and may develop neurological complications. This review article discusses the clinical presentation and laboratory findings in both forms of HIES, as well as the establishment of diagnose, inheritance, molecular genetics and immunological abnormalities of HIES.

Primary immunodeficiencies underlying fungal infections

PURPOSE OF REVIEW

We review the primary immunodeficiencies (PIDs) underlying an increasing variety of superficial and invasive fungal infections. We also stress that the occurrence of such fungal infections should lead physicians to search for the corresponding single-gene inborn errors of immunity. Finally, we suggest that other fungal infections may also result from hitherto unknown inborn errors of immunity, at least in some patients with no known risk factors.

RECENT FINDINGS

An increasing number of PIDs are being shown to underlie fungal infectious diseases in children and young adults. Inborn errors of the phagocyte NADPH oxidase complex (chronic granulomatous disease), severe congenital neutropenia (SCN) and leukocyte adhesion deficiency type I confer a predisposition to invasive aspergillosis and candidiasis. More rarely, inborn errors of interferon-γ immunity underlie endemic mycoses. Inborn errors of interleukin-17 immunity have recently been shown to underlie chronic mucocutaneous candidiasis (CMC), while inborn errors of caspase recruitment domain-containing protein 9 (CARD9) immunity underlie deep dermatophytosis and invasive candidiasis.

SUMMARY

CMC, invasive candidiasis, invasive aspergillosis, deep dermatophytosis, pneumocystosis, and endemic mycoses can all be caused by PIDs. Each type of infection is highly suggestive of a specific type of PID. In the absence of overt risk factors, single-gene inborn errors of immunity should be sought in children and young adults with these and other fungal diseases.

Inborn errors of human IL-17 immunity underlie chronic mucocutaneous candidiasis

PURPOSE OF REVIEW

Chronic mucocutaneous candidiasis (CMC) is characterized by recurrent or persistent symptomatic infection of the nails, skin and mucosae mostly by Candida albicans. CMC is common in patients with profound primary T-cell immunodeficiency, who often display multiple infectious and autoimmune diseases. Patients with syndromic CMC, including autosomal dominant hyper IgE syndrome (AD-HIES) and autosomal recessive autoimmune polyendocrinopathy syndrome type I (APS-I), display fewer other infections. Patients with isolated CMC (CMCD) rarely display any other severe disease. We review here recent progress in the genetic dissection of these three types of inherited CMC.

RECENT FINDINGS

Low IL-17 T-cell proportions were reported in patients with AD-HIES bearing heterozygous STAT3 mutations, prone to CMC and staphylococcal diseases, and in a kindred with autosomal recessive CARD9 deficiency, prone to CMC and other fungal infections. High levels of neutralizing autoantibodies against IL-17 cytokines were documented in patients with APS-I presenting with CMC as their only infectious disease. The first three genetic causes of CMCD were then reported: autosomal recessive IL-17RA and autosomal dominant IL-17F deficiencies and autosomal dominant STAT1 gain-of-function, impairing IL-17-producing T-cell development.

SUMMARY

Inborn errors of human IL-17 immunity underlie CMC. Impaired IL-17 immunity may therefore account for CMC in other settings, including patients with acquired immunodeficiency.

Lung function in hyper IgE syndrome

Pneumatoceles and bronchiectasis are secondary complications of respiratory infections in patients with hyper IgE syndrome (HIgES). We report on a patient with HIgES and recurrent pneumonias since 1 year of age, with progression to pneumatoceles and bronchiectasis and fatal outcome, with disseminated infection and suspected allergic bronchopulmonary aspergillosis, who was subjected to sequential spirometric assessment. We describe the early beginning of respiratory infections, difficulties in the management of pulmonary sequelae and the impact of an early functional diagnosis and follow-up of the patient regarding a disease for which lung function has not been fully described.

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.

Immune defects in active mycobacterial diseases in patients with primary immunodeficiency diseases (PIDs)

Natural human immunity to the mycobacteria group, including Mycobacterium tuberculosis, Bacille Calmette-Guérin (BCG) or nontuberculous mycobacteria (NTM), and/or Salmonella species, relies on the functional IL-12/23-IFN-γ integrity of macrophages (monocyte/dendritic cell) connecting to T lymphocyte/NK cells. Patients with severe forms of primary immunodeficiency diseases (PIDs) have more profound immune defects involving this impaired circuit in patients with severe combined immunodeficiencies (SCID) including complete DiGeorge syndrome, X-linked hyper IgM syndrome (HIGM) (CD40L mutation), CD40 deficiency, immunodeficiency with or without anhidrotic ectodermal dysplasia (NEMO and IKBA mutations), chronic granulomatous disease (CGD) and hyper IgE recurrent infection syndromes (HIES). The patients with severe PIDs have broader diverse infections rather than mycobacterial infections. In contrast, patients with an isolated inborn error of the IL-12/23-IFN-γ pathway are exclusively prone to low-virulence mycobacterial infections and nontyphoid salmonella infections, known as Mendelian susceptibility to the mycobacterial disease (MSMD) phenotype. Restricted defective molecules in the circuit, including IFN-γR1, IFN-γR2, IL-12p40, IL-12R-β1, STAT-1, NEMO, IKBA and the recently discovered CYBB responsible for autophagocytic vacuole and proteolysis, and interferon regulatory factor 8 (IRF8) for dendritic cell immunodeficiency, have been identified in around 60% of patients with the MSMD phenotype. Among all of the patients with PIDs referred for investigation since 1985, we have identified four cases with the specific defect (IFNRG1 for three and IL12RB for one), presenting as both BCG-induced diseases and NTM infections, in addition to some patients with SCID, HIGM, CGD and HIES. Furthermore, manifestations in patients with autoantibodies to IFN-γ (autoAbs-IFN-γ), which is categorized as an anticytokine autoantibody syndrome, can resemble the relatively persistent MSMD phenotype lacking BCG-induced diseases.

Destructive pulmonary staphylococcal infection in a boy with hyper-IgE syndrome: a novel mutation in the signal transducer and activator of transcription 3 (STAT3) gene (p.Y657S)

Hyper IgE syndrome (HIES) is a rare primary immunodeficiency disorder, characterized by eczema, recurrent skin and lung infections, and significantly elevated serum IgE level. It was previously diagnosed based on clinical manifestations and laboratory markers that were not specific to the disease. Recent studies have demonstrated that mutations in signal transducer and activator of transcription 3 (STAT3) cause the autosomal dominant or sporadic HIES, which make the disease definitively characterized at molecular level. Here, we reported a 3-year old Chinese boy with neonatal-onset rash and multiple serious Staphylococcus aureus infections including recurrent skin abscesses, liver abscess, sepsis, and destructive pulmonary infection (pneumonia, multiple pulmonary abscesses, pyopneumothorax, and finally, pneumatocele). Genetic study revealed a heterozygous mutation in exon 21 of STAT3 gene (g.66583 A > C, c.1970A > C) in the boy, which resulted in a substitution of tyrosine at the amino acid position 657 to serine (p.Y657S) in the Src homology 2 (SH2) domain of STAT3. Functional prediction with bioinformatics programs of the Sorting Intolerant from Tolerant (SIFT) and the Polymorphism Phenotyping (PolyPhen) reported "deleterious (SIFT score 0.02)" and "probably damaging (PSIC score difference 2.94)" values, respectively. Further study of family members revealed that neither his parents, nor his twin brother carried the mutation, indicating the mutation was likely to occur de novo in our patient.

CONCLUSION

The mutation,p.Y657S,in SH2 domain of STAT3 is a disease-causing mutation in the boy with HIES.

A proteomic investigation of B lymphocytes in an autistic family: a pilot study of exposure to natural rubber latex (NRL) may lead to autism

Autism is a multi-factorial neurodevelopmental disorder. We have investigated the molecular mechanism involved in a Chinese family with autism by a proteomic approach. Antibody chips containing 500 spots of human protein antibodies were used to screen for differentially expressed proteins in the peripheral B lymphocytes between autistic and non-autistic siblings in this family. Four proteins relevant to immuno-pathway, including IKKα that was up-regulated and Tyk2, EIF4G1 and PRKCI that were down-regulated, were identified differentially expressed in autistic versus non-autistic siblings. Western blot analysis and reverse transcription quantitative polymerase chain reaction validated the differential expression of these four proteins. Based on the function of these differentially expressed proteins, relevant studies on immunoglobulin E (IgE) level, nuclear factor kappa B signaling activation and cell cycle were conducted in both autistic and non-autistic children of this family. Considering the fact that the family members were in close contact with natural rubber latex (NRL) and that IgE-mediated cross-reactions could be triggered by Hevea brasiliensis (Hev-b) proteins in NRL, we hypothesize that immune reactions triggered by close contact with NRL might influence the functions of B lymphocytes by altering expression of certain proteins identified in our experiments thus contributing to the occurrence of autism.

Hyper-IgE syndrome

Hyper-IgE syndrome (HIES) is a complex primary immunodeficiency characterized by atopic dermatitis associated with extremely high serum IgE levels and susceptibility to infections with extracellular bacteria. Nonimmunological abnormalities, including a distinctive facial appearance, fracture following minor trauma, scoliosis, hyperextensive joints, and the retention of deciduous teeth are also observed in most patients. Recent studies have demonstrated that dominant-negative mutations in the signal transducer and activator of transcription 3 (STAT3) gene result in the classical multisystem form of HIES, whereas a null mutation in the tyrosine kinase 2 (TYK2) gene causes an autosomal recessive HIES associated with viral and mycobacterial infections. In both patients, signal transduction for multiple cytokines, including IL-6 and IL-23, was defective, resulting in impaired T(H)17 function. These findings suggest that the defect in cytokine signaling constitutes the molecular basis for the immunological and nonimmunological abnormalities observed in HIES.

Molecular explanation for the contradiction between systemic Th17 defect and localized bacterial infection in hyper-IgE syndrome

Hyper-IgE syndrome (HIES) is a primary immunodeficiency characterized by atopic manifestations and susceptibility to infections with extracellular pathogens, typically Staphylococcus aureus, which preferentially affect the skin and lung. Previous studies reported the defective differentiation of T helper 17 (Th17) cells in HIES patients caused by hypomorphic STAT3 mutations. However, the apparent contradiction between the systemic Th17 deficiency and the skin/lung-restricted susceptibility to staphylococcal infections remains puzzling. We present a possible molecular explanation for this enigmatic contradiction. HIES T cells showed impaired production of Th17 cytokines but normal production of classical proinflammatory cytokines including interleukin 1β. Normal human keratinocytes and bronchial epithelial cells were deeply dependent on the synergistic action of Th17 cytokines and classical proinflammatory cytokines for their production of antistaphylococcal factors, including neutrophil-recruiting chemokines and antimicrobial peptides. In contrast, other cell types were efficiently stimulated with the classical proinflammatory cytokines alone to produce such factors. Accordingly, keratinocytes and bronchial epithelial cells, unlike other cell types, failed to produce antistaphylococcal factors in response to HIES T cell–derived cytokines. These results appear to explain, at least in part, why HIES patients suffer from recurrent staphylococcal infections confined to the skin and lung in contrast to more systemic infections in neutrophil-deficient patients.

Primary immune deficiencies with aberrant IgE production

IgE antibodies play a central role in the pathogenesis of atopic diseases and in host immunity against parasitic infections. IgE has potent activities on mast cells and basophils. IgE class switching is a very tightly controlled process, and serum IgE levels are very low compared with other immunoglobulin isotypes. Transcription factors that activate or inhibit the IgE gene promoter, as well as T(H)1 and T(H)2 cytokines are important in the regulation of IgE levels. Hyper-IgE syndrome; Wiskott-Aldrich syndrome; immunodysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX); Omenn syndrome; and atypical complete DiGeorge syndrome are primary immune deficiencies that are associated with elevated serum IgE levels. Increased IgE levels in IPEX, Wiskott-Aldrich syndrome and Omenn syndrome are likely related to increased T(H)2 cytokine production caused by decreased a number or function of CD4(+)CD25(+)forkhead box protein P3(+) regulatory T cells. The link between signal transducer and activator of transcription 3 mutations and elevated serum IgE levels in hyper-IgE syndrome is unclear. Insight into IgE regulation provided by the study of primary immune deficiencies with elevated IgE has important implications for allergic diseases.

Recent developments related to the laboratory diagnosis of primary immunodeficiency diseases

PURPOSE OF REVIEW

The rapid increases in newly recognized primary immunodeficiency diseases (PIDs), including their clinical, genetic and laboratory-associated abnormalities, make staying abreast of the latest developments a challenge. This review provides an overview of current information directly and indirectly related to the laboratory diagnosis of PIDs.

RECENT FINDINGS

The latest classification and several prevalence studies provide the framework for understanding the breadth, categories and incidence rates of over 120 recognized disease entities. The latter is followed by reviews of new information related to specific PIDs including new tests, new genetic associations and newly discovered laboratory-based abnormalities. The final section presents new PIDs and a discussion of the future potential of array-based technologies in the diagnosis of PIDs.

SUMMARY

The information provided in this review will allow a new appreciation of previously underestimated PIDs' prevalence rates and the delay in their diagnosis. Understanding the molecular causes of PIDs will lead to earlier diagnoses and new targets for improved therapeutic intervention. The presentation of new diagnostic tests should encourage other laboratories to assess their potential in their own laboratories. Ultimately, this information will lead to an increase in the understanding of novel laboratory parameters associated with specific PID and should improve the time required to attain an accurate diagnosis.

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.