This session will cover the roles of Major Histocompatibility Complex (MHC) molecules and T cell receptors (TCRs) in immune responses. MHC molecules present antigens to T cells, with MHC class I presenting to CD8+ cytotoxic T cells and class II to CD4+ helper T cells. TCRs on T cells recognize these antigen-MHC complexes, initiating immune reactions. Clinically, understanding MHC and TCR interactions is crucial for organ transplantation, autoimmune diseases, and immunotherapies. Mismatched MHC molecules can lead to transplant rejection, while abnormal T cell recognition in autoimmune conditions like rheumatoid arthritis and lupus contributes to disease pathogenesis. Additionally, insights into TCRs aid in cancer immunotherapy, where enhancing T cell recognition of tumors holds therapeutic potential. This session will provide an overview of these processes and their clinical implications.