Immunoelectron microscopy of cell populations in regional and central lymph of sheep

The immunoreactivity and the ultrastructural localization of monoclonal anti-sheep lymphocyte antibodies conjugated with colloidal gold particles were examined in free-floating cells of sheep central lymph from the thoracic duct, postnodal lymph draining either the popliteal nodes or the mesenteric nodes, and prenodal lymph draining the pregnant uterus. The monoclonal antibodies used in this study were SBU-T1 (CD5), SBU-T4 (CD4), SBU-T8 (CD8), SBU-II (anti DR antibody), and E53 which are reported to be sheep homologues of human T1, T4, T8, HLA-DR, and pan B cell antibodies, respectively. Colloidal gold particles were evenly distributed or segmentally aggregated on the surfaces of lymphocytes and macrophages incubated with monoclonal antibodies and in vesicles in the cytoplasm of anti DR antibody labeled macrophages. Not only did CD5 labeled cells show a high percentage in each regional lymph examined, but the percentage of CD4 labeled cells was consistently higher than that of CD8 labeled cells. Moreover, the immunoreactivity of CD8 labeled cells was specific among lymph from the different regions. The sum of the percentages of CD4 and CD8 labeled cells was less than the percentage of CD5 labeled cells, indicating the presence of a minor T cell subpopulation which was CD5+, CD4-, and CD8-. A characteristic finding was a high percentage of CD8 labeled cells and many abnormal eosinophils in uterine prenodal lymph in pregnant sheep. Taken together the results showed that variously labeled immunoreactive cells are distributed somewhat differently in lymph derived from different organ sites.