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The MOST ABUNDANT antibody class in human blood is:

AIgA (mucosal secretions like saliva)
BIgM (first response to infection)
CIgG (majority of circulating antibodies)
DIgE (mediator of allergic reactions)
Answer & Solution
Correct answer: C. IgG (majority of circulating antibodies)
IgG is the most abundant antibody (~75% of serum antibodies), crosses the placenta to provide passive immunity to the foetus. IgM is the first to appear in infection. IgE mediates allergies.
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