Where does affinity maturation of antibodies predominantly occur?

• A. Thymic cortex
• B. Spleen red pulp
• C. Germinal centers of lymph nodes
• D. Bone marrow

Answer: (C)

Affinity maturation is the process by which B cells refine their antibodies to bind antigens more tightly, and it happens in germinal centers within secondary lymphoid organs. After an antigen is encountered, B cells form germinal centers in lymph nodes (and also in the spleen). Inside these centers, B cells rapidly mutate their antibody genes in the dark zone (somatic hypermutation driven by AID) and then test these variants in the light zone by presenting antigen to follicular helper T cells. Those with higher affinity receive survival and proliferation signals, while lower-affinity cells are outcompeted. This selective process enriches for B cells producing high-affinity antibodies and also generates memory B cells and long-lived plasma cells. The other sites listed aren’t where this affinity-enhancing selection primarily occurs: the thymic cortex is for T cell development, and the bone marrow is where B cells develop and plasma cells can form, but not where affinity maturation via germinal-center selection takes place. The spleen does have germinal centers, but the classic, most emphasized location for this process is the germinal centers of lymph nodes.