<prompt> The HLA class III region genes are important elements inTransplant rejection phenomenonAntigen presentation and eliminationImmune surveillanceGoverning susceptibility to autoimmune diseases  <response>: HLA class III region contains genes for early complement components C2 and C4 of classical pathway.Deficiency of these early components of the classical pathway viz C1, C2 and C4 is associated with autoimmune diseases like SLE and other collagen vascular diseases. These genes are thus, important in regulating susceptibility to autoimmune disease Class III genes do not participate in MHC restriction or graft rejection components. 