The immunosuppressive activity of C1q degradation peptides.

We have previously reported the existence and activity of a collagen-like, low molecular weight, suppressive peptide complex in patients with greater than 40% BSA burns. Since C1q participates in the inflammatory response and contains a collagen-like sequence, we have tested, in vitro, the putative generation and immunologic activity of C1q peptide fragments under physical conditions present in burned patients. Nanogram quantities of heat- and enzyme-generated fragments of C1q were shown to be suppressive in vitro to neutrophil chemotaxis, and the mixed lymphocyte response (MLR). The addition of lymphocytes pretreated with C1q fragments suppressed ongoing MLR, indicating the activation of suppressor cells by the peptides. Rabbit anti-C1q globulin was found to reduce the suppressive activity of the collagen-like suppressor which was isolated from human burn sera. Our results therefore suggest that C1q may be an early source of degradation peptides which have strong nonspecific immunosuppressive activity following thermal injuries.