Cyclic AMP mediated modulation of complement protein production.

We have investigated the mechanisms by which cAMP analogues and phosphodiesterase inhibitors, reduced the production of C2 by monocytes in culture. Pulse label studies with 3H-labelled aminoacids showed that dibutyryl cAMP (dbcAMP) impaired the secretion of newly synthesised protein, both total (acid-precipitable) and individual complement proteins (precipitated antibody by antisera to C4, C2, C3, C5, B, P, C3b inactivator and beta 1H). The intracellular degradation of newly synthesised protein was increased in dbcAMP-treated cultures and protein synthesis was reduced. Studies aimed at defining the temporal relationships between these changes showed that protein secretion was impaired on the first day of culture, and increased degradation of newly synthesised protein was obvious by day 2. Protein synthesis was not significantly reduced until day 3 of culture. It is proposed that changes in intracellular cAMP levels may act as a second signal in the control of protein production by monocytes.