Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.
One may wonder why the genes for the class III region are even situated in the human Major Histocompatibility Locus (MHC). However, on closer inspection we find that the genes for the complement components, tumor necrosis factor (TNF) and others may play an important role in host immune defenses. Thus, this region on chromosome six may be more appropriately thought of as an immune response area. Accordingly, there is a high degree of polymorphism in many genes within the MHC, the most notable being the HLA genes. In the class III region C2, factor B (Bf) and C4 are polymorphic in as many populations studied to date. The purpose of this review will be to briefly describe the class III region, identify the genetic polymorphism found in various ethnic groups and define their roles in autoimmune diseases.