Dominant-negative mutations in
STAT3 cause a multisystem disorder that is characterized by eczema, recurrent staphylococcal infections of the skin and lungs, pneumatocele formation, mucocutaneous candidiasis, eosinophilia, elevated serum IgE, and various non-immune manifestations [
3**,
11**,
12*].
Most immunological manifestations of AD-HIES are driven by
Staphylococcus aureus infections of the skin and lung. More than half of patients with AD-HIES present with a newborn rash – sometimes present at birth – consisting of eosinophilic pustules [
3**,
11**]. Nearly all patients develop unusual
S. aureus skin abscesses that lack the usual redness, warmth, or pain (termed “cold abscesses”). These infections also induce eczematoid dermatitis.
S. aureus also causes the majority of sinopulmonary infections in AD-HIES, with
Streptococcus pneumoniae and
Haemophilus species responsible for most of the remainder. Lung infections can usually be controlled by antibiotics, but abnormal lung repair often results in the development of pneumatoceles and bronchiectasis. Lung cyst formation occurs in 75% of patients. Parenchymal damage predisposes to chronic and opportunistic infections, including
Aspergillus, Pseudomonas aeruginosa,
Pneumocystis jirovecii, and atypical
Mycobacteria.
The pathophysiological mechanisms by which
STAT3 mutations contribute to
S. aureus bacterial infections are beginning to be understood. STAT3 is a transcriptional factor that is activated in response to various cytokines and growth factors, including interleukin (IL-6), IL-10, IL-22, IL-23, and macrophage colony-stimulating factor. Mutant STAT3 interferes with the signaling pathway downstream of these cytokine receptors, resulting in a complex array of altered immune responses [
4,
13,
14]. For example, STAT3-dependent transcription mediated by IL-6, IL-22, and IL-23 binding to their specific receptors are essential for the differentiation of T helper type 17 (Th17) cells, which normally promote protective myeloid responses against extracellular bacteria and fungi by secreting IL-17A and IL-17F. Interestingly, a recent study suggested that keratinocytes and bronchial epithelial cells respond synergistically to both IL-17 and classical proinflammatory cytokines, e.g., tumor necrosis factor-alpha, IL-1β, and interferon (IFN)-γ, whereas other cell types, such as leukocytes, can compensate by responding to classical proinflammatory cytokines alone. Because of the lack of Th17 cells in AD-HIES, keratinocytes and bronchial epithelial cells produce less neutrophil chemoattractants and antimicrobial peptides [
13]. These observations could explain why infections are localized to skin and lung but do not occur systemically. Furthermore, neutrophils from AD-HIES patients have decreased expression of chemoattractant receptors [
15], which could also explain why the sites of infection often show minimal inflammation.
In addition to problems with localized bacterial infections, 40% of the patients also have fungal infections, which include mucocutaneous candidiasis, Histoplasmosis, and
Cryptococcus neoformans [
11**,
12*]. This is explained by the defective production of Th17 cells, as mentioned above. Moreover, the IL-17 produced in mucosa normally induces the production of histatins in saliva, so its deficiency could explain the high frequency of thrush in AD-HIES patients [
16*]. Together, these observations support an important role for the lack of Th17 cells in the immunopathogenesis of AD-HIES.
AD-HIES features skeletal, dental and connective tissue abnormalities [
11**,
17]. By the time they are teenagers, ~90% of patients develop a characteristic asymmetric facies with deep-set eyes, prominent forehead and chin, and bulbous nose. Half of patients have increased interalar distance, cathedral palate, and central depressions of the tongue. Failure to exfoliate primary teeth is also common. Some patients show hyperextensibility, bone fractures following minimal trauma, and scoliosis. Moreover, surprisingly high frequencies of coronary artery tortuosity or dilation (70%), aneurysms (37%), and hypertension (42%) have been reported [
18*]. These non-immunological manifestations reflect the broad expression and function of STAT3 in many tissues, and help to distinguish AD-HIES from AR-HIES.
Additionally, several cases of malignancy have been reported in AD-HIES [
11**,
19*–
21*]. Among the patients who were confirmed as having
STAT3 mutations, non-Hodgkin’s lymphoma and diffuse large B-cell lymphoma were the most common [
19*–
21*].
The autosomal dominant or sporadic cases of Job’s syndrome are caused by heterozygous missense mutations in
STAT3 [
4–
6]. Loss-of function mutations have not been identified in patients, arguing against a haploinsufficiency mechanism of disease pathogenesis. In normal individuals, STAT3 forms dimers upon stimulation, which translocate into the nucleus and bind to DNA to promote gene expression. However, in patients who express mutant and wild-type STAT3 proteins, abnormal dimers form. These abnormal dimers lead to dominant negative effects, although the precise mechanisms for these effects remains unclear. Mutational hot-spots, which are predominantly located in the DNA binding or SH2 (src-homology 2) domains, as well as other mutations in the transactivation or coiled-coil domains, have been reported [
3**]. However, available data do not currently support any genotype-phenotype correlations [
22].