A new biologic role for C3a and C3a desArg: regulation of TNF-alpha and IL-1 beta synthesis.

The complement activation products C3a and C3a desArg are generated in the course of trauma, infection, tissue injury, and ischemia. We have investigated the effects of C3a and C3a desArg on gene expression and protein synthesis of TNF-alpha and IL-1 beta in PBMC. Neither C3a nor C3a desArg alone induced detectable protein or mRNA levels for TNF-alpha and IL-1 beta. C3a modulated LPS-induced TNF-alpha and IL-1 beta synthesis. In nonadherent PBMC, C3a suppressed LPS-induced synthesis of TNF-alpha (20-71% decrease by 0.2-10 microgram/ml of C3a, p less than 0.01) and IL-1 beta (19-57% decrease by 0.5-10 microgram/ml of C3a, p less than 0.01), independently of endogenous production of PGE2. C3a also suppressed LPS-induced mRNA levels for TNF-alpha and IL-1 beta. In contrast, in adherent PBMC, C3a at 5 to 20 microgram/ml enhanced LPS-induced TNF-alpha (75-188% increase, p less than 0.001) and IL-1 beta (119-274% increase, p less than 0.001) synthesis. C3a enhanced TNF-alpha and IL-1 beta mRNA levels in LPS-stimulated adherent cells. Furthermore, C3a desArg shared with C3a the ability to modulate LPS-induced mRNA and protein synthesis for TNF-alpha and IL-1 beta. These results suggest that C3a, thought to be proinflammatory, and C3a desArg, thought to be biologically inactive, are modulators of inflammation. Both C3a and C3a desArg may enhance cytokine synthesis by adherent monocytes at local inflammatory sites, while inhibiting the systemic synthesis of proinflammatory cytokines by circulating cells.