The antigen-specific T cell receptor (TCR) is composed of either alpha and beta subunit, or gamma and delta subunit. Majority of T cells present in the blood, lymph and secondary lymphoid organs express TCR alpha/beta heterodimers, whereas the T cells expressing TCR gamma/delta heterodimers are localized mainly in epithelial tissues and at the sites of infection. The subunits of TCR heterodimers are covalently bonded and in the endoplasmic reticulum they associate with CD3 subunits to form functional TCR-CD3 complex. Lack of expression of any of the chains is sufficient to stop cell surface expression.Specificity : The mouse monoclonal R73 recognizes an extracellular epitope TCR alpha/beta, the dominant subtype of T cell receptor expressed in peripheral blood.