A 5-year-old boy presents with recurrent Staphylococcal skin abscesses, elevated IgE (>2000 IU/mL), eczema, and coarse facies. Neutrophil count is normal. Which functional defect underlies this condition?

• A Impaired STAT3 signalling causing defective Th17 differentiation ✓
• B Absent adenosine deaminase causing lymphocyte apoptosis
• C Defective CD18 causing neutrophil adhesion failure
• D Absent IL-12 receptor reducing IFN-gamma production

Explanation

Hyper-IgE syndrome (Job's syndrome) is caused by dominant-negative STAT3 mutations. STAT3 is critical for Th17 cell differentiation; without Th17 cells, IL-17-mediated neutrophil recruitment at mucosal surfaces and skin fails, allowing Staphylococcal infections. The paradox is 'cold' abscesses — pus collection without surrounding warmth/erythema — because the local inflammatory response is blunted. ADA deficiency causes SCID, CD18 defect causes LAD-I, and IL-12R deficiency causes susceptibility to mycobacteria.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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