Surface Ig-mediated events occurring in normal B cells or in FL B cells after entry into the GC. (A) Normal B cells encounter antigen in the T-cell zone and then locate in a GC where SHM, antigen selection, and isotype switching occur. Antigen, held as immune complexes on follicular dendritic cells, selects B cells of appropriate affinity. After interaction with specific T cells, selected B cells proliferate and differentiate before leaving the site to develop into memory B cells or plasma cells. (B) B cells that have undergone the t(14;18) translocation can respond to antigen and undergo SHM in a GC. Introduced N-glycosylation motifs in the Ig variable regions are positively selected by FL cells. Interaction of the added mannoses with lectins can occur and might provide a foundation for development of FLIS or overt FL in the GC site. B cells that do not acquire N-glycosylation motifs can exit, and possibly revisit, the GC.