Antibody-dependent cellular cytotoxicity of Trypanosoma theileri mediated by purified bovine isotypes and subisotypes

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Abstract
Bovine neutrophils, eosinophils and macrophages mediated in vitro cytotoxicity against T. theileri in the presence of purified IgM, IgG1 and IgG2 from immune bovine serum. When the immunoglobulin fractions were assayed at similar concentrations, IgM was the most effective isotype mediating killing with all 3 effector cell types. Using the ELISA with monospecific antisera against the different bovine isotypes and subisotypes, IgM was shown to be contaminated by < 1%. The addition of 0.08 M 2-mercaptoethanol inhibited IgM-mediated ADCC but not that of IgG1 or IgG2, and the cytotoxicity occurred in the absence of complement. The presence of isotype and subisotype specific Fc receptors on the bovine effector cells was investigated using a totally homologous erythrocyte-antibody (EA) rosetting technique. FC receptors for bovine IgM, IgG1 and IgG2 were detected on bovine neutrophils. Very few FcM receptors were detected on either eosinophils or macrophages, but FcG2 receptors were detected on both cell types, and FcG1 receptors on macrophages. Eosinophils showed very few FcG1 receptors. The failure to detect all types of Fc receptor on the 3 different effector cells is discussed.