Murine complement factor C4, formerly known as Gg protein, consists of an alpha-, beta-, and gamma-chain. The classical pathway of complement and the Mannose binding lecting activation pathway converge at C4. C1s, MASP-1 and MASP-2 cleave C4 resulting in the formation of C4a and C4b. the latter can be cleaved to result in C4c and C4d in which step all functional sires are lost. The C7850-16B reacts with intact C4, C4b, C4d. C4 is an acute phase protein that is produced by hepatocytes, monocytes and intestinal epithelial cells.