This entry represents complement C1q subcomponent B. C1q is a complex of nine proteins, six are disulfide-linked dimers of the A and B chains, and three are disulfide-linked dimers of the C chain []. C1q combines with C1r and C1s to form the first complement in the complement activation cascade, C1 []. C1qB contains two collagen-like domains, and a C-terminal C1q domain.