Complement Component C1q, Human Serum

Complement subcomponent C1q is composed of three polypeptide chains (A, B, and C). C1q associates with C1r and C1s to set up the first component of the serum complement system. Activation of the complement system is induced by interaction with the Fc regions of IgG or IgM antibodies within immune complexes, enhancing the ability of those antibodies and cells of the immune system to attack pathogens. C1q deficiency is associated with lupus and glomerulonephritis.