T-cell receptors are membrane-bound proteins found on T-cells , which recognize antigen peptides presented on the MHC of Antigen Presenting Cells . T-cell Receptors differ from B-cell antibodies in that they cannot bind free antigens. For a T-cell receptor, the antigen must be presented on a MHC protein. In the case of helper T-cells, the antigen peptides must be presented on Class II MHC, and in the case of killer T-cells , the antigen peptides must be presented on Class I MHC.

The T-cell antigen receptor consists of either an alpha/beta chain (TCR-2) or a gamma/delta chain (TCR-1) associated with the CD3 molecular complex.