C4B Antibody

Background:

This gene encodes the basic form of complement factor 4,part of the classical activation pathway. The protein is expressedas a single chain precursor which is proteolytically cleaved into atrimer of alpha, beta, and gamma chains prior to secretion. Thetrimer provides a surface for interaction between theantigen-antibody complex and other complement components. The alphachain may be cleaved to release C4 anaphylatoxin, a mediator oflocal inflammation. Deficiency of this protein is associated withsystemic lupus erythematosus. This gene localizes to the majorhistocompatibility complex (MHC) class III region on chromosome 6.Varying haplotypes of this gene cluster exist, such thatindividuals may have 1, 2, or 3 copies of this gene. In addition,this gene exists as a long form and a short form due to thepresence or absence of a 6.4 kb endogenous HERV-K retrovirus inintron 9.