T cell receptor antigen complex. Molecular model of the alphabeta T cell receptor bound to the influenza haemagglutinin antigen and MHC class II molecule HLA-DR1. T cell receptors are protein complexes found on the surface of a type of white blood cell called T lymphocytes (or T cells), part of the body's immune system. Antigens (foreign proteins) are presented to T cell receptors by MHC molecules to effect an immune response.