T-cell receptor-MHC-antigen complex - stock illustration

Computer illustration of a T-cell receptor (purple) binding to an MHC-antigen complex (orange and green). The antigen (light green) is a peptide from a tumour cell, bacteria or virus. A number of cells present antigens to lymphocytes via membrane bound major histocompatibility complex (MHC) molecules (orange). After binding to the MHC-antigen complex, the T-cell receptor sends a signal cascade into the T-lymphocyte cell that activates an immune response.