Selective IgA deficiency — Which class of pathogens/problems would most likely increase in a patient lacking IgA?
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ARecurrent extracellular bacterial infections of deep tissues only
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BBacteremia after dental work due solely to bloodstream entry
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CMucosal pathogens at respiratory, gastrointestinal, and genitourinary surfaces
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DPathogens that survive exclusively inside macrophages (strict intracellular bacteria)
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EParasitic infections cleared only by eosinophils and IgE
Answer
Correct Answer: Mucosal pathogens at respiratory, gastrointestinal, and genitourinary surfaces
Explanation
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:
1) Identify IgA’s location and function → mucosal neutralization.2) Map likely pathogens → mucosal bacteria, viruses, and parasites that colonize these surfaces.3) Choose the option emphasizing mucosal risk across systems.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:
a) Deep tissue extracellular infections are less specifically linked to IgA loss.b) Transient bacteremia after procedures is more related to barrier disruption than IgA alone.d) Control of strictly intracellular pathogens relies on cell-mediated immunity.e) Eosinophils/IgE address helminths; IgA loss does not uniquely point to this.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.