In T cell dependent B cell activation, what happens in germinal centers?

• A. Class switching and affinity maturation occur, producing higher-affinity antibodies (e.g., IgG, IgA, IgE).
• B. IgM is produced with no class switching.
• C. All activation occurs without T cell help.
• D. Antibody responses are confined to the extrafollicular region.

Answer: (A)

In germinal centers during T cell dependent B cell activation, B cells refine their antibodies through two coordinated processes. Somatic hypermutation in the immunoglobulin variable regions creates a spectrum of B cell receptors with different affinities, and those with higher affinity are selected in the light zone with ongoing help from follicular helper T cells. At the same time, class switch recombination is driven by cytokines from T helper cells, changing the antibody constant region to isotypes like IgG, IgA, or IgE while preserving the antigen specificity. The result is antibodies with higher affinity and different effector functions, rather than the initial IgM response produced without such maturation.