Regulation of IgM and IgD synthesis in B lymphocytes. I. Changes in biosynthesis of mRNA for mu- and delta-chains.

Although IgD is expressed on the surface of resting B cells at a higher density than IgM, we determined that both the steady-state level and the biosynthetic rate of mu m-mRNA is higher than that of delta m-mRNA, suggesting that translational or post-translational processing of the Ig heavy chains may modulate the expression of cell surface Ig. After B cell activation by LPS, delta m-mRNA decreases drastically, accounting for the observed decrease in expression of IgD. Concomitantly, a dramatic increase in the level of mu s- and gamma s-mRNA corresponds to the observed increase in secretion of these Ig isotypes in LPS-stimulated cells.