<prompt> Cell mediated lysis of tumor cells is mediated by?HLA1HLA2HLA3All of the above  <response>: Ans is a i.e. HLA1 HLA complex consists of three separate clusters of genes :-1 Class I MHC-I It comprising of A, B and C loci i.e. HLA-A, HLA-B, HLA-C. It is found on the surface of all nucleated cells and platelets. Important cells with MHC-I HLA-I on surface are B-cells, T-cells, macrophagesmonocytes, neutrophils, langerhans cells, dendritic cells, platelets thrombocytes, epithelial cells of thymus and hepatocytes. MHC class I present antigen to cytotoxic CD-8 T cells MHC-I restricted. MHC class I is responsible for graft rejection and cell mediated cytolysis of viral infected or tumor cells.2 Class II MHC-II It comprises D region HLA-DR, HLA-DQ, HLADP. It is found only on the cells of immune system, i.e. T-cells, B-cells, langerhans cells, dendritic cells, and macrophages. MHC-II recognizes exogenous antigen extracellular microbes, soluble proteins and present it to CD4 helper T cells MHC-II restricted. MHC-II is responsible for graft versus host response and mixed leukocyte reaction.3 Class III MHC-III It encodes for complement components C2 C4, properdin factor B, Heat shock protein and Tumor necrosis factor-a and b TNF-a and b. MHC-III is involved in susceptibility to autoimmune diseases like SLE. 