Selective IgA deficiency — Which class of pathogens/problems would most likely increase in a patient lacking IgA?

Introduction:
IgA is the dominant immunoglobulin at mucosal surfaces, where it neutralizes pathogens and toxins without inducing intense inflammation. Selective IgA deficiency is among the most common primary immunodeficiencies and predisposes patients to mucosal infections and some allergic/autoimmune phenomena.

Given Data / Assumptions:

• Secretory IgA (sIgA) is transported across epithelia via the poly-Ig receptor.
• sIgA neutralizes microbes and toxins in the lumen at mucosal surfaces.
• Other isotypes (e.g., IgG, IgM) may partially compensate systemically but not fully at mucosa.

Concept / Approach:
Predict the clinical vulnerability based on the anatomic niche where IgA dominates. Loss of IgA mainly impairs first-line defense at respiratory, GI, and GU mucosa, leading to recurrent otitis media, sinusitis, bronchitis, diarrhea, and related infections.

Step-by-Step Solution:

Verification / Alternative check:
Clinical cohorts show increased respiratory and GI infections and sometimes Giardia in IgA deficiency; serum IgG often remains normal, explaining relatively preserved systemic responses.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming serum antibody levels predict mucosal protection; overlooking the specialized transport and polymeric form (dimer) of sIgA.

Final Answer:
Mucosal pathogens at respiratory, gastrointestinal, and genitourinary surfaces.