Precursor B Cells Showing H Chain Allelic Inclusion Display Allelic Exclusion at the Level of Pre-B Cell Receptor Surface Expression

Abstract

Within the pools of μH chain–producing precursor and mature B cells from normal and λ5-defective mice, the frequency of cells in which both H chain alleles were productively V HDJ H rearranged was determined. An equally high percentage (2%–4%) of cells carrying two productively V HDJ H-rearranged H chain loci was found in precursor and mature B cell pools of both mouse strains. In all of these cells, one allele encodes a μH chain incapable of forming a surface-expressed pre-B cell receptor. Hence, allelic exclusion is maintained at the level of pre-B cell receptor expression. The surprising conservation of H chain allelic exclusion in λ5-defective B cells suggests that an alternative form of pre-B cell receptor might function to ensure this allelic exclusion.