C4A

Complement component 4 (C4), in humans, is a protein involved in the intricate complement system, originating from the human leukocyte antigen (HLA) system, which when paired with complement component 2 (C2) is imperative in generating an immune response. C4 serves a number of critical functions in immunity, tolerance, and autoimmunity with the other numerous components. Furthermore, it is a crucial factor in connecting the recognition pathways of the overall system instigated by antibody-antigen (Ab-Ag) complexes to the other effector proteins of the innate immune response. For example, the severity of a dysfunctional complement system can lead to fatal diseases and infections and even emotional and mental disorders like schizophrenia. The C4 protein was initially thought to be derived from a simple two-locus allelic model, but in more recent years, popular scientific consensus has grown around a more sophisticated multi-modular RCCX gene complex model. This RCCX multi-modular model, contains long and short forms of the C4A or C4B genes which are usually in tandem with RCCXcassettes; or a mobile genetic element often containing a specific gene or set of genes along with a recombin