Three monoclonal antibodies identifying antigens on all equine T lymphocytes, and two mutually exclusive T-lymphocyte subsets.

The aim of this study was to produce monoclonal antibodies (mAb) recognizing equine lymphocyte surface antigens. Fusions were conducted using BALB/c mice hyperimmunized with equine thymocytes. Hybridoma supernatants were screened by flow cytometry and positive hybridomas were cloned twice by limiting dilution. These mAb were then characterized for tissue distribution by immunohistology and flow cytometry, and by precipitation and analysis of the lymphocyte antigens which they recognized. Three mAb (CVS5, CVS4 and CVS8) are described which recognize only T lymphocytes in peripheral blood. Two-colour immunofluorescent studies showed that CVS5 recognized all T lymphocytes and that CVS4 and CVS8 recognized two mutually exclusive subsets of CVS5-positive cells. In the thymus there was a large population of CVS4/CVS8 double-positive cells. Immunohistochemical staining with these mAb was restricted to T-lymphocyte areas. CVS4 and CVS5 precipitated molecules of 58,000 and 69,000 MW, respectively, in both reducing and non-reducing conditions. CVS8 precipitated two molecules of 32,000 and 39,000 MW in reducing conditions, and one molecule of 69,000 MW in non-reducing conditions. This evidence suggests that CVS5, CVS4 and CVS8 recognize the equine homologues of CD5, CD4 and CD8, and that the characteristics of these antigens are similar to those of other species.