Identification of a molecule uniquely expressed on a gamma/delta TCR+ subset within bovine intestinal intraepithelial lymphocytes.

An antigen has been identified, recognized by a novel monoclonal antibody CC45, which is expressed by a subpopulation of bovine gamma/delta T-cell receptor-positive (gamma/delta TCR+) T cells restricted in their distribution to the intestinal epithelium. This subset of intestinal intraepithelial lymphocytes (iIEL) which represented 8-29% of gamma/delta TCR+ T cells in the gut epithelium expressed CD45, CD3 and L-selectin; most of these cells were CD2- and CD8-. Electron microscopic studies of CC45+ cells revealed that they were large mononuclear leucocytes containing numerous mitochondria and smooth vesicles; a proportion of these contained membrane-bound dense granules. Immunoprecipitation of 125I-labelled iIEL analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis under reducing and non-reducing conditions revealed polypeptides of 60,000 and 200,000 molecular weights, respectively indicating that the antigen, which appears distinct from molecules described in other species, is expressed on the cell surface as a complex.