The control of production of the membrane (m) vs secreted (s) forms of immunoglobulin heavy chains was investigated in a panel of cell lines expressing different heavy chain classes but identical light chains (λ) and variable regions. These cell lines could be induced towards Ig secretion by mitogen treatment. During this process a shift from m to s heavy chain production takes place. Here we show that, similarly to IgA- and IgE-producing B cells, in IgG2a-producing I.29 cells the γm-γs shift was accompanied by a shift in the corresponding mRNAs, with a decrease of γm mRNA and an increase of the γs mRNA in LPS-stimulated cells. By contrast, the μm mRNA was increased in LPS-stimulated IgM-producing cells, albeit these cells synthesized reduced amounts of μm polypeptides. The utilization of the translational level in the early steps of B lymphocyte maturation thus distinguishes the mode of regulation of μ chains from those of the other isotypes. In addition, in B cells a post-translational event blocks the secretion of IgM but not of IgG or IgE.
ASJC Scopus subject areas
- Molecular Biology