CENTROCYTES RAPIDLY ADOPT A MEMORY B-CELL PHENOTYPE ON COCULTURE WITHAUTOLOGOUS GERMINAL CENTER T-CELL-ENRICHED PREPARATIONS

B cells, after mutating their Ig V-region genes in germinal centres (G C), undergo apoptosis, unless they receive antigen-dependent selection signals, The signals appear to be delivered by GC T cells, require CD 40 ligand expression and may induce differentiation to memory cells, C ultured GC a cells are prevented from entering apoptosis by ligating t heir surface CD40, but the resulting phenotype is not that associated with a cells found in vivo. Conversely, GC a cells rapidly adopt a mem ory B cell phenotype on culture with autologous memory CD4(+) T cells that have been induced to express CD40 ligand transiently, This effect is prevented by blocking CD40 ligand, Naive CD4(+) T cells, induced t o express CD40 ligand, do not prevent GC B cells undergoing apoptosis.