BOVINE CELLS INFECTED IN-VIVO WITH THEILERIA-ANNULATA EXPRESS CD11B, THE C3BI COMPLEMENT RECEPTOR

Bovine cells from cattle infected with Theileria annulata were phenoty ped with monoclonal antibodies recognizing bovine leukocyte antigens. Macroschizont-infected, transformed cell lines prepared from periphera l blood mononuclear cells of cattle, infected with sporozoites, were a ssessed by dow cytometry; parasitized cells in tissues from infected c attle were examined by immunocytochemical techniques. Co-expression of markers for different cell lineages by the cell lines precluded a def inite conclusion as to their phenotypic origins. For, while the patter n of leukocyte antigens expressed by; these in vivo-derived schizont-i nfected cells, which included CD11b, was indicative of a myeloid origi n, the possibility that they were NK cells could not be excluded. The monoclonal antibody (MAb) IL-A15, which recognizes CD11b, reacted with a high proportion of parasitized cells in sections of tissues from in fected cattle at all stages of acute disease. Mononuclear cells infect ed with parasites at all stages of differentiation, from macroschizont to microschizont, expressed CD11b. Such parasitized cells occurred th roughout the lymphoid tissues, being found in the thymus, spleen and l ymph nodes, particularly the prescapular node draining the site of inf ection, the hepatic, mesenteric and precrural nodes, as well as in the reticulo-endothelial tissue of the liver, kidney, lung, abomasum, adr enal and pituitary glands. These observations provided the first evide nce for a myeloid origin for the parasitized T. annulata cells found i n infected bovine tissues and blood and suggested a mechanism whereby schizonts could transfer from cell to cell during mechanical infection with schizont-infected cells.