Question:
Some antigen was injected into a rabbit. Which antibody will it produce initially?
Some antigen was injected into a rabbit. Which antibody will it produce initially?
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First exposure means primary response; think of the pentameric antibody made first.
Updated On: Jun 24, 2026
- IgG
- IgM
- IgA
- IgD
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The Correct Option is B
Solution and Explanation
Step 1: The question describes a first encounter with antigen, that is, a primary immune response.
Step 2: In a primary response, naive B cells are activated and initially secrete antibody without prior class switching.
Step 3: The first immunoglobulin class produced is IgM, a pentamer with ten antigen-binding sites that is highly efficient at complement activation and agglutination early in infection.
Step 4: Only later, after T cell help and class switching, do IgG and other isotypes predominate; IgG is the main antibody of the secondary (memory) response.
Conclusion: The antibody produced initially is IgM, so the answer is option 2.
Step 2: In a primary response, naive B cells are activated and initially secrete antibody without prior class switching.
Step 3: The first immunoglobulin class produced is IgM, a pentamer with ten antigen-binding sites that is highly efficient at complement activation and agglutination early in infection.
Step 4: Only later, after T cell help and class switching, do IgG and other isotypes predominate; IgG is the main antibody of the secondary (memory) response.
Conclusion: The antibody produced initially is IgM, so the answer is option 2.
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