ADAPTIVE IMMUNE RESPONSES Clonal Expansion of B Cells and T Cells Antigen-recognizing naïve B cells, follicular dendritic (fDC) cells, and follicular helper T (Tfh) cells are in follicles of the lymph nodes, spleen, and MALT. Primary follicles due to the B-cell clonal expansion develop into secondary follicles. The B cells are stimulated into mitosis during which they grow into centroblasts and then as centrocytes depending on a stage of the process in the secondary follicle's center. The B cells with the highest affinity due so-called somatic hypermutations will be selected to differentiate into plasma cells, which produce antibodies. The T-cell clonal expansion proceeds in paracortical zones of the lymph nodes, periarterial lymphatic sheaths of the spleen and parafollicular zones of the MALT. Former naïve T cells are stimulated into proliferation and turned into lymphoblasts, which then become effector T lymphocytes and memory T cells. ©V.V.Klimov