Complement component 4

Complement component 4 is a protein involved in the complement system.

It is cleaved into proteins 4a and 4b; 4b can be further cleaved into 4c and 4d.

Clinical significance

It is responsible for the Chido Rodgers blood group system.

C4d has been identified as a biomarker for systemic lupus erythematosus.

The gene that codes for C4 is being investigated for the role it may play in schizophrenia risk and development.

References

C4A

Complement C4-A is a protein that in humans is encoded by the C4A gene.

Function

This gene encodes the acidic form of complement factor 4, part of the classical activation pathway. The protein is expressed as a single chain precursor which is proteolytically cleaved into a trimer of alpha, beta, and gamma chains prior to secretion. The trimer provides a surface for interaction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4 anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemic lupus erythematosus and type I diabetes mellitus. This gene localizes to the major histocompatibility complex (MHC) class III region on chromosome 6. Varying haplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene.

See also

References

Further reading