Characterization of two sheep lymphocyte differentiation antigens, SBU-T1 and SBU-T6

The monoclonal antibodies 25.91 and 20.27 define two lymphocyte cell surface antigens of sheep. 25.91 is reactive with 60-80% of lymphocytes and 98% of thymocytes, and only stains surface immunoglobulin-negative peripheral lymphocytes. 25.91 immuno-precipitates a 67,000 MW protein from lymphocyte lysates under both reducing and non-reducing conditions, whereas immunoprecipitation of thymocyte lysates reveals a 67,000, 62,000 MW complex. The tissue distribution and molecular weight analysis reported here for the antigen recognized by 25.91 indicate that this antigen is the sheep homologue of the human T1 and mouse Ly 1 antigens. The monoclonal antibody 20.27 is reactive with 80% of thymocytes and the majority of cell surface immunoglobulin-positive peripheral blood lymphocytes (B cells), but is unreactive with peripheral blood T cells. 20-27 also stains Langerhans cells in skin tissue sections and large dendritic-like cells in the paracortex sections and large dendritic-like cells in the paracortex of lymph node tissue sections. Immunoperoxidase staining of thymus tissue sections with 20.27 shows intense staining of cortical thymocytes and an absence of staining within the medulla. Molecular weight analysis of the 20.27 antigen reveals two major bands of 46,000 and 12,000 MW under both reducing and non-reducing conditions. The 20.27 antigen has properties resembling MHC class I-like antigens such as T6 in the human and TL in the mouse.