This gene encodes the B-chain polypeptide of serum complement subcomponent C1q, which associates with C1r and C1s to yield the first component of the serum complement system. C1q is composed of 18 polypeptide chains which include 6 A-chains, 6 B-chains, and 6 C-chains. Each chain contains an N-terminal collagen-like region and a C-terminal C1q globular domain. C1q deficiency is associated with lupus erythematosus and glomerulonephritis.C1QB (Complement C1q B Chain) is a Protein Coding gene. Diseases associated with C1QB include C1q Deficiency and Immunodeficiency Due To A Classical Component Pathway Complement Deficiency. Among its related pathways are Innate Immune System and Complement Pathway. GO annotations related to this gene include protein homodimerization activity. An important paralog of this gene is C1QC.