The changing preference of T and B cells for partners as T-dependent antibody responses develop

Summary: Recirculating virgin CD4⁺ T cells spend their life migrating between the T zones of secondary lymphoid tissues where they screen the surface of interdigitating dendritic cells. T-cell priming starts when processed of interdigitating dendritic cells. T-cell priming starts when processed peptides or superantigen associated with class II MHC molecules are recognised. Those primed T cells that remain within the lymphoid tissue move of the outer T zone, where they interact with B cells that have taken up and processed antigen. Cognate interaction between these cells initiates immunoglobulin (Ig) class swith-recombination and proliferation of both B and T cells; much of this growth occurs outside the T zones. B cells both B and T cells; much of this growth occurs outside the T zones. B cells migrate to follicles. Where they form germinal centres, and to extrafollicular sites of B-cell growth, where they differentiate into mainly short-lived plasma cells. T cells do not move to the extrafollicular foci but to the follicles; there they proliferate and are subsequently involved in the selection of B cell that have mutated their Ig variable-region genes. During primary antibody responses T-cell proliferation in follicles produces many times the peak number of T cell found in that site; a substantial proportion of the CD4⁺ memory T-cell pool may originate from growth in follicles.