The effects of C-reactive protein on human cell-mediated cytotoxicity.

C-reactive protein (CRP) is a trace serum protein that increases markedly in concentration during inflammatory reactions. Although CRP, in the presence of a multivalent ligand, binds in vitro to a small percentage of peripheral blood lymphocytes from normal donors and is present on natural killer (NK) cells, exogenous addition of CRP has few effects on human lymphocytes. CRP causes minimal enhancement of proliferation in a mixed lymphocyte culture and a slight increase in 3H-thymidine uptake by unstimulated cells. The most significant effect of CRP is a substantial increase in cell-mediated cytotoxicity (CMC). In this publication, we show that CRP dramatically enhances the alloantigen-activated cytotoxic response only when it is present at the initiation of culture and that pretreatment of responder cells with CRP will not produce enhancement. Although the CMC enhancement generated the presence of CRP is not antigen specific, it is mediated by a T cell, and neither NK-like cells nor monocytes are involved in mediating CRP enhanced killing.