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Pathology · single question

What is the primary function of secretory IgA in saliva?

  1. It directly lyses bacterial cell walls
  2. It provides mucosal immune defense by blocking bacterial/viral adherence to oral mucosal surfaces (immune exclusion)
  3. It functions mainly as a digestive enzyme
  4. It promotes blood clot formation
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Correct answer: B. It provides mucosal immune defense by blocking bacterial/viral adherence to oral mucosal surfaces (immune exclusion)

Secretory IgA is the predominant immunoglobulin in saliva. Rather than killing microbes directly, it works mainly through 'immune exclusion' — agglutinating microorganisms and blocking their adhesion receptors so they cannot colonize the mucosa, complementing innate factors like lysozyme and lactoferrin.

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