Which class of immunoglobulin antibodies is predominantly found in external bodily secretions such as saliva, tears, colostrum, and mucus?
Answer and explanation
Correct answer: C. IgA
- Step 1: Review antibody isotypes and physiological distributions.
- Step 2: Secretory IgA (dimeric form) is the primary antibody protecting mucosal surfaces against pathogen colonization in saliva, tears, breast milk, and respiratory secretions.
Answer
IgA.
Why not the others: IgG is the most abundant serum antibody crossing the placenta; IgE mediates allergic reactions and anti-parasitic responses; IgM is the primary pentameric acute-phase antibody.
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