Generation of C5-derived peptides and other immune reactants in the sera of patients with systemic lupus erythematosus.

Activated complement components and immune complexes cause neutrophil aggregation in vitro and in vivo. We have previously demonstrated that sera of patients with active systemic lupus erythematosus (SLE) provoke the aggregation of normal neutrophils in vitro. In this study the serum or plasma of 4 such patients was fractionated on Sephadex G-75. In 3 patients neutrophil aggregating activity (NAA) was detectable in fractions which coeluted with reference C5-derived peptides (estimated molecular radius of 17,000). The activity of these fractions was inhibitable by antibodies to human C5. All patients also had activity that coeluted with reference immune complexes. In addition, material of apparent molecular radius under 12,000 that contributed to the neutrophil aggregating activity of SLE sera was detected. In separate experiments increased levels of C5a desarg were demonstrated during active disease by means of radioimmunoassay. These findings suggest that multiple neutrophil aggregants circulate during the course of active SLE. The formation of intravascular leukoaggregates may contribute to endothelial injury in this disease.