Diagrammatic representation of B-cell differentiation and relationship to major B-cell neoplasms. B-cell neoplasms correspond to stages of B-cell maturation, even though the precise cell counterparts are not known in all instances. Precursor B cells that mature in the bone marrow may undergo apoptosis or develop into mature naive B cells that, following exposure to antigen and blast transformation, may develop into short-lived plasma cells or enter the germinal center (GC), where somatic hypermutation and heavy chain class-switching occur. Centroblasts, the transformed cells of the GC, either undergo apoptosis or develop into centrocytes. Post-GC cells include both long-lived plasma cells and memory/marginal zone B cells. Most B cells are activated within the GC, but T cell–independent activation can take place outside of the GC and also probably leads to memory-type B cells. Monocytoid B cells, many of which lack somatic hypermutation, are not illustrated. AG indicates antigen; and FDC, folllicular dendritic cell. Red bar represents immunoglobulin heavy chain gene (IGH@) rearrangement; blue bar, immunoglobulin light chain gene (IGL) rearrangement; and black insertions in the red and blue bars indicate somatic hypermutation.