The R78 antibody recognizes the specific T cell receptor beta chain Vbeta 8.2/8.4. The TCR beta chain interacts with the TCR alpha chain and CD3 to form an antigen binding and signaling complex. TCR alpha and beta are members of the immunoglobulin superfamily expressed on most peripheral T cells, intestinal epithelial lymphocytes, and thymocytes. TCR Vbeta 8.2/8.4 is expressed on a subset of TCR alpha/beta-bearing T cells. The CD3/TCR complex plays a key role in antigen recognition, signal transduction, and T cell activation. The alpha/beta TCR recognizes peptide bound to MHC class I and II. The R78 antibody is useful for the analysis of T cell receptor repertoire.