T-cell antigen receptor

The T-cell receptor (TCR) is a crucial component of the immune system, specifically involved in acquired immunity. Unlike B cells that secrete antibodies into body fluids, T cells with TCRs cannot bind to free-floating antigens. Instead, they recognize fragments of foreign proteins displayed on the surface of body cells, often in conjunction with major histocompatibility complex (MHC) molecules.12

There are different types of T cells, including helper T cells (CD4+) that activate other immune cells, and cytotoxic T cells (CD8+) that destroy infected or cancerous cells. The TCR, along with accessory molecules like CD4 or CD8, binds to these antigen-MHC complexes, initiating a cellular response to threats like viruses that have already entered cells. This recognition is highly specific, ensuring that the immune system targets only the foreign invaders.312