Complement C1q, Human Plasma
Human Complement Component 1q (C1q) is a high molecular weight complex of six trimers, each consisting of an A, B, and C chain. Complement C1 is the first component in the classical complement cascade and circulates in plasma as a calcium-dependent complex of C1q, C1r, and C1s. C-terminal C1q globular domains bind to Fc regions of IgM or IgG present in immune complexes while N-terminal C1q collagen-like regions interact with the C1r2C1s2 proenzyme complex. C1q circulates in normal serum at 113 ug/ml. Patients deficient in C1q are prone to systemic lupus erythematosus (SLE) and glomerulonephritis as well as recurrent infection and skin lesions. Specific Haemolytic Complement activity is determined by lysis of antibody sensitized sheep red blood cells with C1q deficient human serum. Prepared from plasma shown to be non reactive for HbsAG, HTLV-I/II, STS, and negative for anti-HCV, anti-HIV-1, and anti-HIV-2 by FDA approved tests. >98percent pure by SDS-PAGE.