Frequencies of multiple IgL chain gene rearrangements in single normal or κL chain-deficient B lineage cells

PCR analyses of the kappa L chain locus in single B-lineage cells of wild-type, C kappa-, or JC kappa-deficient homozygous or heterozygous mice often detect multiple in- and out-of-frame rearrangements at the kappa L and lambda L loci. They are most frequent in small pre-BII cells and equally so in wild-type and kappa L chain-deficient cells. Hence, kappa L chain production appears not to inhibit secondary rearrangements. Around 20% of all small preBII cells express IgL chains in their cytoplasm. Cells with a first productive rearrangement on one allele are favored to enter the immature B cell compartment. Thus, allelic exclusion might be secured by control of accessibility of IgL chain loci for rearrangement and by rapid selection of cells with a fitting over those with a nonfitting IgL chain.