Pattern of C3, iC3b, and C3d in patients hospitalized for acute asthma.

Twenty-three patients hospitalized for acute asthma were studied for a peripheral blood complement profile consisting of C3, C4, C3d, iC3b, C4d, and Bb concentrations. Compared with normals (n = 22) and patients (n = 10) with acute bacterial infections (ABI), asthmatic patients had significantly higher serum C3 concentrations (P less than .001). Plasma C3d levels and iC3b in asthmatic patients were both comparable to those observed in normal controls, whereas patients with ABI had significantly higher iC3b levels than both other groups. The ratio of iC3b to C3 concentrations were similar in asthmatic patients and controls, and iC3b levels were correlated with total serum C3 levels in asthmatic patients (r = .55, p less than .001) as well as in normal (r = .69, p less than .001). Both of these groups had significantly lower iC3b to C3 ratios compared with the ABI group (P less than .0001). Also observed in asthmatic patients were a significant correlation between serum C4 and C3 levels (r = .83, P less than .001) and a lower mean ratio of plasma C4d to C4 compared with normals (P less than .005). This profile of complement alterations is distinct from that observed in acute bacterial infection. These changes in asthmatic patients may relate to an acute phase reaction phenomenon affecting complement and/or complement regulatory proteins.