Q.82 Which of the following statements about the primary and secondary adaptive
immune responses to an antigen is/are correct?
(A) IgM antibodies appear first in response to the initial exposure of the antigen.
(B) Majority of the antibodies produced in response to the second exposure of the same
antigen are IgM isotype.
(C) Second exposure of the same antigen stimulates production of memory cells.
(D) Primary antibody response has shorter lag phase than secondary antibody response.
(A) Correct. IgM antibodies are the first to appear during the initial exposure to an antigen in the primary adaptive immune response, as naive B cells rapidly produce IgM before class switching occurs.
(B) Incorrect. In the secondary response to the same antigen, the majority of antibodies produced are IgG, not IgM, due to class switching and activation of memory B cells.
(C) Correct. The second exposure activates pre-existing memory cells generated during the primary response, leading to a faster and stronger antibody production.
(D) Incorrect. The primary antibody response features a longer lag phase (4-7 days) compared to the shorter lag phase (1-3 days) in the secondary response.
Correct options: (A) and (C).
Primary and secondary adaptive immune responses to antigens form the cornerstone of immunological memory, enabling faster pathogen clearance upon re-exposure. These responses differ in antibody types, timing, and intensity, critical for exams like CSIR NET Life Sciences.
Primary Response Features
Naive B cells activate upon first antigen encounter, producing IgM antibodies after a lag phase of 4-7 days. Levels peak lower, then decline, while memory cells form for future protection.
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IgM appears first due to no initial class switching.
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Weaker overall antibody output.
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Generates memory B and T cells.
Secondary Response Features
Memory cells trigger a rapid response on re-exposure, with IgG as the dominant isotype after a 1-3 day lag. Antibody levels surge 100-1000 times higher and persist longer.
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Shorter lag phase enables quick defense.
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Higher affinity IgG predominates.
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Stronger, sustained protection.
Option Analysis Table
| Option | Statement | Correct? | Explanation |
|---|---|---|---|
| (A) | IgM first in initial exposure | Yes | Matches primary response kinetics. |
| (B) | Majority IgM in second exposure | No | IgG dominates secondary. |
| (C) | Second exposure stimulates memory cells | Yes | Memory cells drive rapid response. |
| (D) | Primary has shorter lag than secondary | No | Primary lag longer (4-7 days). |
