The alpha chain of a T cell receptor (TCR) for antigens is one of the membrane-bound heterodimers. The other heterodimer is the beta chain. Each chain contains one variable (V) region and one constant (C) region. The V and C regions are homologous to immunoglobulin (B cell receptor for antigens) V and C regions. In the V region of each TCR chain there are three hypervariable, or complementarity-determining (CD), regions. As is the case for antibodies, CDR3 is the most variable among different TCRs.[1]