Role of the Igh intronic enhancer E? in clonal selection at the pre-B to immature B cell transition.

ABSTRACT: We previously described a checkpoint for allelic exclusion that occurs at the pre-B cell to immature B cell transition and is dependent upon the IgH intronic enhancer, E?. We now provide evidence that the breach in allelic exclusion associated with E? deletion results from decreased Ig? levels that make it difficult for emerging BCRs to reach the signaling threshold required for positive selection into the immature B cell compartment. We show that this compartment is smaller in mice carrying an E?-deficient, but functional, IgH allele (VH?(a)). Pre-B cells in such mice produce ? 50% wild-type levels of Ig? (mRNA and protein), and this is associated with diminished signals, as measured by phosphorylation of pre-BCR/BCR downstream signaling proteins. Providing E?-deficient mice with a preassembled VL gene led not only to a larger immature B cell compartment but also to a decrease in "double-producers," suggesting that H chain/L chain combinations with superior signaling properties can overcome the signaling defect associated with low Ig?-chain and can eliminate the selective advantage of "double-producers" that achieve higher Ig?-chain levels through expression of a second IgH allele. Finally, we found that "double-producers" in E?-deficient mice include a subpopulation with autoreactive BCRs. We infer that BCRs with IgH chain from the E?-deficient allele are ignored during negative selection owing to their comparatively low density. In summary, these studies show that E?'s effect on IgH levels at the pre-B cell to immature B cell transition strongly influences allelic exclusion, the breadth of the mature BCR repertoire, and the emergence of autoimmune B cells.

SUBMITTER: Peng C 

PROVIDER: S-EPMC3810302 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature