The alpha chain of a T cell receptor

T cell receptor

The T cell receptor or TCR is a molecule found on the surface of T lymphocytes that is responsible for recognizing antigens bound to major histocompatibility complex molecules...

 (TCR) for antigen

Antigen

An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

s 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

Hypervariable

Hypervariable may refer to:*Hypervariable sequence, a segment of a chromosome characterised by considerable variation in the number of tandem repeats at one or more loci...

, or complementarity-determining (CD), regions. As is the case for antibodies

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

, CDR3 is the most variable among different TCRs.