Hypocomplementemia with low C1s-C1 inhibitor complex in systemic lupus erythematosus.
Ninety-three serum and plasma samples from 45 patients with systemic lupus erythematosus were analyzed for the complex formed by C1s and its inhibitor, as well as for C3, C4, C4a desarginine, and staphylococcal protein A-bound immune complexes. There were statistically significant correlations between C1s-C1 inhibitor complex and CH50, between C1s-C1 inhibitor complex and C4, and between C1s-C1 inhibitor complex and C4a desarginine. Serial studies were performed on 24 patients over a period of 6 months. Seven of 21 patients with hypocomplementemia had persistently normal levels of C1s-C1 inhibitor complex, 7 had transiently abnormal levels of C1s-C1 inhibitor complex, and 7 had sustained abnormal levels of C1s-C1 inhibitor complex. Two of 3 pregnant patients with normal levels of complement had abnormal levels of C1s-C1 inhibitor complex. Staphylococcal protein A-bound immune complexes demonstrated no correlation with any of the complement assays. Complement activation, as measured by C1s-C1 inhibitor complex, is often a transient phenomenon in systemic lupus erythematosus patients with persistent hypocomplementemia.
D000936:Antigen-Antibody Complex / Q000032:analysis / Q000276:immunology; D003166:Complement Activating Enzymes / Q000037:antagonists & inhibitors; D003174:Complement C1 Inactivator Proteins / Q000097:blood*; D003173:Complement C1s; D003176:Complement C3 / Q000032:analysis; D003181:Complement C4 / Q000031:analogs & derivatives / Q000032:analysis; D015934:Complement C4a; D003165:Complement System Proteins / Q000032:analysis*; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood*; D011247:Pregnancy; D013205:Staphylococcal Protein A / Q000276:immunology
D000936:Antigen-Antibody Complex; D003174:Complement C1 Inactivator Proteins; D003176:Complement C3; D003181:Complement C4; D013205:Staphylococcal Protein A; C051066:complement C4a, des-Arg; D015934:Complement C4a; D003165:Complement System Proteins; D003166:Complement Activating Enzymes; D003173:Complement C1s