How do T cells recognize antigens?

T cells recognize antigens through their T cell receptors (TCRs), which are proteins present on the surface of T cells. 

After protein antigens have been partly degraded inside antigen-presenting cells (APCs), the peptide fragments are carried to the surface of the presenting cell by specialized host-cell glycoproteins that are encoded in a gene complex known as the major histocompatibility complex (MHC). MHC proteins present the fragments to T cells, which recognize the antigens through their T cell receptors. This interaction between the TCR and the antigen-MHC complex activates the T cell, leading to an immune response against the antigen.