Germinal center

A germinal center is a transient microanatomical structure that forms in secondary lymphoid organs during an adaptive immune response. It is the physical site where B cells undergo somatic hypermutation and clonal selection to produce affinity-matured memory B cells and plasma cells. The germinal center partitions this evolutionary process into two distinct zones: a dark zone of rapid proliferation and mutation, and a light zone of antigen-mediated selection. This spatial architecture transforms a population of B cells into a distributed optimization algorithm, with the geometry of the center itself acting as the computation substrate. The germinal center does not merely house affinity maturation; it *is* affinity maturation made physical.