It is generally accepted that T and B lymphocytes are able to receive antigenic stimuli because they have a structure on their surface that corresponds (is complementary) to the conformation of the antigenic determinant cluster, which is called an “antigen receptor”. Antigen receptors are specific, so T and B cells are both antigen-specific lymphocytes. The antigen receptor of B cells is a membrane structural protein embedded in the lipid bilayer called membrane surface immunoglobulin (SmIg). Each lymphocyte clone has a receptor that recognizes only one antigenic determinant cluster, and each lymphocyte can produce only one specific antibody, which is the basis for monoclonal antibodies that react only against one antigenic determinant cluster. There are millions of lymphocyte clones in the body, so the body is able to recognize a variety of different antigenic foreign substances and thus an immune response occurs. The T cell receptor (TCR) is present on the surface of antigen-specific T cells in a complex with CD3. These molecules include CD4, CD8, MHCI, MHCII-like molecules, lymphocyte function-associated antigen-1 (LFA-1), intercellular adhesion molecule-1 (ICAM-1, or CD54), LFA-2 (CD2), and LFA-3 (CD58). The polypeptide chains are heterogeneous and four types of polypeptide chains, a, b, g and d, have been identified depending on the antigen structure and encoding genes, and can be divided into two types, abTCR and gdTCR, depending on their composition. most TCRs are abTCR, in which CD4+abTCR T cells recognize non-self MHCII-like antigens (alloantigens) or their own MHCII-like antigens in complex with foreign antigens. Recognition of foreign antigens by abTCRs requires processing by antigen presenting cells (APC), where foreign antigens bind to MHC antigens on the surface of the APC to form a complex that can be recognized by Th cells. A few TCRs are composed of gd chains, and the physiological functions of gdTCRs in vivo are not fully understood.