Effects of Phorbol Esters on B‐Cell Gene Expression

Splenic B lymphocytes were stimulated with lipopolysaccharide alone or in combination with phorbol-12,13-dibutyrate, a protein kinase C-activating phorbol ester. The effect of the treatment was analysed at the single cell level with in situ RNA/RNA hybridization. Hybridization with a kappa light chain probe revealed that the whole population had shifted towards a low, but significant, expression of immunoglobulin mRNA. Analysis at the population level was performed by DNA/RNA and RNA/RNA hybridization experiments. It was found that the steady-state levels of mRNA for kappa light chain, IgM heavy chain and J chain were reduced by phorbol ester treatment, while the steady-state level of mRNA for IgD heavy chain was increased. Steady-state levels of mRNA for Ia antigen and alpha-actin were marginally affected.