Figure 6.

A proposed model for the induction of receptor editing and cell death during B cell development. Productive light chain rearrangements allow progression of pre-B cells to the immature, IgM⁺/recombination⁺ (recomb.⁺) phenotype that, in the absence of antigen, matures to a transitional, IgM^bright/recombination⁻ stage (positive selection). In the presence of antigen (pathway marked “1”), however, this transition does not occur, allowing continued expression of VJ recombination, new light chain gene expression, and receptor editing. If receptor editing extinguishes self-specificity, the IgM⁺/recombination⁺ B cell can resume its maturation. However, if an appropriate receptor cannot be made, the cell eventually dies, but no more quickly than a cell that is unable to assemble in-frame rearrangements during the small pre-B II stage. In this sense, antigen reactivity in the IgM⁺/recombination⁺ B cell does not directly accelerate B cell death, but blocks differentiation. In contrast, transitional, IgM^bright/recombination⁻ B cells encountering antigen (pathway marked “2”) are reported to be highly sensitive to rapid antigen-induced death (18).