The effect of T cell-derived lymphokines on the levels of isotype-specific RNA in normal B cells.

T cell-derived lymphokines, known as B cell differentiation factors (BCDF), play a critical role in the regulation of B cell differentiation. These BCDFs are present in the supernatants (SN) of a long-term alloreactive T cell line, PK 7.1. In this report we present evidence that B cells cultured with lipopolysaccharide (LPS) and BCDFs express increased levels of both the secreted and membrane forms of gamma 1 mRNA. The appearance of mRNA for the membrane form of mu precedes the appearance of mu secreted form mRNA. Approximately 1 day later, appearance of membrane and secreted forms of gamma 3 and gamma 1 can be detected with the membrane forms of both isotypes peaking earlier than the corresponding secreted forms. The mRNAs for both the membrane and secreted forms of gamma 3 are suppressed in the presence of LPS and PK 7.1 SN while LPS alone induces an increase in both. Quantification of newly synthesized nuclear and cytoplasmic RNA for mu, gamma 3, and gamma 1 RNA suggests that PK 7.1 SN down-regulates levels of gamma 3 RNA by decreasing its transcription. In contrast, it may increase level of gamma 1 RNA by effects exerted at the post-transcriptional level. Taken together, these results demonstrate that T cell-derived lymphokines can act on B cells by regulating the levels of nuclear and cytoplasmic RNA specific for gamma 1 and gamma 3.