Characterization of bovine haemopoietic progenitor cells using monoclonal antibodies and fluorocytometry.

Monoclonal antibodies against bovine leucocyte cell surface differentiation antigens were used in combination with a fluorescence activated cell sorter to enrich bovine haemopoietic progenitor cells present in bone marrow cell populations prior to in vitro culture. After two sequential centrifugations of the bone marrow cell suspension through Ficoll-Paque, the interface fraction was stained with a cocktail of monoclonal antibodies directed against mature monocytes/macrophages, granulocytes and lymphocytes. Using appropriate electronic window settings on a FACStar Plus, cells with a high 90 degrees light scattering property (granular cells), a low forward light scattering property (erythrocytes and reticulocytes) and cells positive for monoclonal antibodies specific for lineage-restricted leucocyte markers were removed and the negative cell fraction collected. These negatively-selected cells were stained with monoclonal antibodies specific for a pan-leucocyte or a MHC class II marker and the positive cell population was collected in a second sort and subsequently submitted to culture. All erythroid and granulocyte/macrophage colony forming cells expressed MHC class II antigens, as well as the pan-leucocyte antigen. These same progenitors did not bind any of a variety of monoclonal antibodies directed against lineage-specific antigens on lymphocytes, granulocytes or monocytes/macrophages, although they did bind monoclonal antibodies recognizing MHC class I antigens. Between 85% and 91% of the isolated cells seeded were capable of forming erythroid or granulocyte/macrophage colonies within 5 to 10 days, thus increasing the plating efficiency of these cell types in bone marrow populations by at least 60 fold.