Transitional B cells lose their ability to receptor edit but retain their potential for positive and negative selection.

Ligation of B cell receptors on immature bone marrow B cells, either by an endogenous Ag or by an anti-B cell receptor Ab induces secondary V(D)J gene rearrangements, termed receptor editing. Whether the same signal induces receptor editing in transitional B cells is not clear. In this study, we examined the responses of immature and transitional B cells from V(H)12Vkappa1A Ig transgenic mice to stimulation with an anti-Igbeta Ab. Our results demonstrated that immature B cells stimulated with a low concentration of anti-Igbeta Ab, mimicking Ag stimulation, underwent receptor editing both in vivo and in vitro, as evidenced by the detection of dsDNA breaks at Jkappa recombination signal sequences, whereas transitional B cells did not. The lack of dsDNA breaks in transitional B cells contrasts with their increased expression of RAG1 and RAG2, suggesting a novel mechanism that may prevent rearrangements. Furthermore, treatment of transitional B cells with high concentrations of anti-Igbeta Abs induced apoptosis, whereas low concentrations induced differentiation. Our results support the idea that transitional B cells lose the capacity to edit, but are sensitive to positive and negative selection.