(complement c4) A glycoprotein that is important in the activation of CLASSICAL COMPLEMENT PATHWAY. C4 is cleaved by the activated COMPLEMENT C1S into COMPLEMENT C4A and COMPLEMENT C4B.

(complement c4) An early component of the classical and mannose binding lectin (MBL) complement activation pathways. C4 is consumed by proteolysis upon activation of the classical and MBL pathways, but not the alternative pathway. C4 levels are generally low in active immune complex diseases mediated by classical or MBL activation, but not alternative activation, with the canonical example being systemic lupus erythematosus.

(complement component-4) Complement component-4 (1744 aa, ~193 kDa) is part of the complement cascade, which mediates the innate immune response to infection. The full length protein is a precursor that is secreted as a trimeric molecule containing an alpha, beta and gamma chain. When the complement cascade is initiated, the protein is cleaved. This proteolysis releases both the alpha chain, C4 anaphylatoxin, which stimulates inflammation, and a dimer of the beta and gamma chains, which mediates the interaction between the antigen-antibody complex and other complement components.