Describe the course of events that results in the swollen lymph nodes characteristic of many infections. Use the following terms in your answer:

Question

B lymphoblasts, centroblasts, centrocytes, follicular dendritic cells, germinal center, primary focus, primary follicle, somatic hypermutation, boundary region, and tingible body macrophages.

What will be an ideal response?

Answer 1

B lymphoblasts that have bound specific antigen and encountered their cognate T cells in the boundary regions between primary follicles and the T-cell area of a lymph node are activated and start to proliferate, forming a primary focus. The B cells move from the primary foci into primary follicles, which are primarily B-cell areas, where they become centroblasts—large, metabolically active, dividing cells. As centroblasts accumulate and proliferate, the primary follicle enlarges and changes morphologically into a germinal center. Centroblasts undergo somatic hypermutation while dividing in the germinal center, producing centrocytes with mutated surface immunoglobulin. Only cells with mutated surface immunoglobulin that can take up antigen efficiently through receptor-mediated endocytosis and present it to helper T cells (TFH) will be selected to differentiate into plasma cells or memory cells. Antigen will be encountered at the surface of follicular dendritic cells as an immune complex. If B cells do not encounter their specific antigen, they will undergo apoptosis and then be ingested and cleared by tingible body macrophages. This process takes around 7 days after an infection begins, and the increase in cell numbers due to lymphocyte proliferation accounts for the swollen lymph nodes.