Mode of regulation of immunoglobulin mu- and delta-chain expression varies during B-lymphocyte maturation.

The transcription, processing, and accumulation of mu and delta mRNA was studied in several cell lines representing different stages of B-lymphocyte maturation. Our results indicate that the relative content of mu and delta mRNA is the major determinant of the IgM versus IgM + IgD phenotype and that the production of delta mRNA is regulated at distinctly different levels of gene expression in early and later developmental stages. In B cell lymphomas typical of early stages, transcription extends over the entire 25 kb of the mu- delta locus and the relative content of mu and delta mRNA is determined at the level of mRNA processing. In contrast, in cells typical of mature IgM secretors, transcription is terminated abruptly between the mu and delta genes, precluding the production of delta mRNA. We propose a model that accounts for qualitative and quantitative changes in mu-delta expression in the developing B lymphocyte.