Canine MHC‐class II antigens on B and T lymphocytes¹

MHC‐class II antigens on canine lymphoid cells were detected with monoclonal antibodies (Mabs). On the basis of reactivity with resting or activated T lymphocytes two groups of Mabs were reported earlier. Non‐activated T lymphocytes expressed MHC‐class II antigens recognized by the first group whereas the second group recognized only MHC‐class II antigens on activated T lymphocytes. In this study we analysed the reactivity pattern of both groups of Mabs with purified canine B lymphocytes. One‐ and two‐colour immunoflowcytometric analysis, immu‐noprecipitation, immunohistology and MLC inhibition were performed. The Mabs which only reacted with activated T lymphocytes appeared to stain also purified slg⁺ lymph node cells. Two‐colour fluorescence and immunohistology confirmed the reactivity of these Mabs with B lymphocytes. Immunoprecipitation showed the bimolecular structure of these antigens. It was concluded that two subsets of MHC‐class II antigens can be detected on canine lymphoid cells. One subset showed an aberrant distribution being expressed on both nonactivated and activated T and on B lymphocytes. The second subset of MHC‐class II antigens could only be detected on B lymphocytes and activated T lymphocytes, a distribution pattern similar to that found in most other species, for instance man.