The first component of complement,C1,is a calcium-dependent complex of the 3 subcomponents C1q,C1r,and C1s. C1q is composed of 18 polypeptide chains: six A-chains,six B-chains,and six C-chains. Each chain contains a collagen-like region located near the N terminus and a C-terminal globular region. Deficiency of C1q has been associated with lupus erythematosus and glomerulonephritis. This antibody is raised against C1qC which is the C-chain polypeptide of human complement subcomponent C1q.