IgM RNA switch from membrane to secretory form is prevented by adding antireceptor antibody to bacterial lipopolysaccharide-stimulated murine primary B-cell cultures

Abstract

Bacterial lipopolysaccharide (LPS) induces proliferation of resting primary murine B lymphocytes and their differentiation into Ig-secreting cells. This is accompanied by an increase in the rate of Ig gene transcription and the accumulation of μ heavy chain secretory mRNA. Specific antiantigen receptor antibody (anti-μ) induces resting B cells to proliferation but not differentiation. Upon addition of both LPS and anti-μ to cultures, resting B cells again proliferate but do not differentiate. RNA transfer blots of the Ig mRNA 2 days after induction with LPS/anti-μ show a specific deficiency of the 2.4-kilobase (kb) μ secretory mRNA, whereas the levels of the 2.7-kb μ membrane and 1.2-kb κ light chain mRNAs are as high as in cells treated with LPS alone. Between days 3 and 4 after treatment with both reagents, reductions of μ membrane and, to a smaller extent, κ mRNA become apparent. As measured by nuclear run-on transcription experiments at day 2, the transcription rates of Ig μ and the Ig κ transcription units are equal in both induction experiments. Only at later stages do the LPS/anti-μ-treated cells transcribe Ig genes at a lower rate. Thus, the anti-μ treatment, drastically reducing the μ secretory mRNA production at early stages, represents a negative regulation occurring primarily at the posttranscriptional level.