How does the secondary humoral immune response differ from the primary response?

• A. The lag phase is longer in the secondary immune response.
• B. IgM is the predominant antibody class produced in the secondary immune response.
• C. The antibody levels produced are higher in the secondary immune response.
• D. Cytotoxic T lymphocytes play an important role in the secondary response.

Answer: (C)

The main idea is that memory from the first exposure makes the second response much more robust. After the initial encounter, B cells that recognize the antigen become memory B cells. When the same antigen appears again, these memory cells quickly react and differentiate into plasma cells that dump out large amounts of antibody. Because these are already specialized and have undergone affinity maturation, the antibodies produced are not only in greater quantity but also of higher affinity. In practice, the secondary humoral response is fast and yields a high titer of antibody, predominantly IgG, with improved quality.

That’s why the correct statement is that antibody levels produced are higher in the secondary immune response. The other points aren’t characteristic of the secondary response: the lag phase is shorter, not longer; IgM is not the predominant antibody in the secondary response (IgG is); and cytotoxic T lymphocytes are a cellular immunity component, not the primary driver of the humoral (antibody-mediated) secondary response.