<s>[INST] context: Sho arm of chr- 6 Human leucocyte antigen is so called because it was first discovered on the leucocytes. HLA is also called Major histocompatibility complex. The histocompatibility antigens (human leukocyte antigens - HLA) are cell surface antigens that induce an immune response leading to rejection of allogrufts. The principal physiologic function of the cell surface histocompatibility molecules is to bind peptide fragments of foreign proteins for presentation to antigen specific T cells. The histocompatibility antigens are encoded by a closely linked multiallelic cluster of genes, Major histocompatibility complex (MHC) or Human leukocyte antigens complex (HLA complex). - HLA complex of genes is located on the sho arm of chromosome 6. It consists of three separate clusters of genes: HLA Complex [MHC Responses of MHC molecules Class 1 MHC class I molecules bind and process peptide that are derived from proteins synthesized within the cells, e.g. viral protein in viral infected cells and antigen of cancerous cells. These cells (cancerous or virus infected) have a tendency to display unusual, non self antigens on their surface. After binding to MHC-I, these antigens are processed and presented to cytotoxic CD-8 T cells (MHC-I restricted). Cytotoxic CD-8 T cell - MHC I reaction cause -- Graft rejection - Cell mediated cytolysis of viral infected or tumor cells. Class II Class 11 molecules present exogenous antigen (e.g. extracellular microbes, soluble proteins). These antigens are first internalized and undergo proteolytic cleavage in lysosome. Peptide generated .from this proteolytic cleavage are presented by MHC - II to CD4-T cells (MHC-II restricted). Reactions are : - Graft versus host response - Mixed leukocyte reaction Class III "The MHC class HI region contains many genes that are good candidates for the involvement in autoimmune disease". Recent data suggest that quantitative and qualitative diversities of the MHC Ill linked C4 among different ethnic groups can be impoant in susceptibility to autoimmune disease like SLE. Note ? The pa of MHC complex that code for TNF a & /land heat shock protein, is also referred as class IV MHC. [/INST] question: HLA is located on aEUR' | options: A: Sho arm of chr-6 B: Long arm of chr-6 C: Sho arm of chr-3 D: Long arm of chr-3 | answer: A </s>