Description
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