Antibody-Dependent Cell-Mediated Cytotoxicity in Cattle: Activity Against 51Cr-Labeled Chicken Erythrocytes Coated with Protozoal Antigens

Bovine mononuclear cells in the presence of bovine anti-chicken erythrocyte sera at high dilutions induce release of chromium-51 from labeled chicken erythrocytes. Bovine effector cells are capable of recognizing both bovine immunoglobulin G 1 and bovine immunoglobulin G 2 ; in contrast, human effector cells only recognize immunoglobulin G 1 . Effector cell activity of bovine mononuclear cells is equally distributed between peripheral blood and spleen. As in other species, thymus and lymph node cells exert no antibody-dependent effect, although some direct cytotoxicity by lymph node cells may be observed. Antibody-dependent cell-mediated cytotoxicity against a bovine cell line can also be detected. By using a tannic acid technique, it was found that chicken erythrocytes coated with Theileria parva piroplasm antigen or with Trypanosoma rhodesiense variant-specific coat antigen form suitable targets for bovine antibody-dependent cell-mediated cytotoxicity assays. By using such targets, a moderate degree of direct cytotoxicity by bovine mononuclear cells, in the absence of antibody, is always observed; this may be reduced by choosing optimal conditions of tannic acid treatment and antigen sensitization and by the use of short incubation periods for the cytotoxicity assay. Observations have been made on the variant specificity, time course of appearance, and association with immunoglobulin G 1 of the antibody activity responsible for cell-dependent cytotoxicity against chicken erythrocytes coated with T. rhodesiense antigens. The potential usefulness of this technique in the analysis of protective immune responses against protozoal infections is discussed.