Selective peripheral expansion and activation of B cells expressing endogenous immunoglobulin in μ-transgenic mice

Abstract

Two different lines of C57BL/6 mice (IgH^b) carrying complete rearranged μ chain genes from BALB/c (IgM^a) were analyzed for the expression and secretion of endogenous as well as transgenic immunoglobulins at the level of single cells. Quantitation of B cells expressing endogenous IgM^b by cytofluorometry, limiting dilution analyses of clonal precursors and secretory cell assays revealed a marked selective expansion, activation and terminal differentiation of those cells producing endogenous immunoglobulins. Thus, the very infrequent IgM^b−bearing B cells produced in bone marrow of transgenic mice accumulate in spleen, where they are activated and account for roughly half of all natural immunoglobulin‐secreting cells. These observations indicate that μ‐transgenic mice are valuable in studies of the antibody repertoire selection operating in unprimed animals but their use could be misleading in the analyzing ''monoclonal'' immune system.