Inhibition of in vitro immunocyte function by sera from cattle with bovine leukosis

Most sera from leukaemic cattle inhibited phagocytic activity of normal bovine peripheral polymorphonuclear leukocytes, growth of interleukin 2-dependent bovine T cells and mitogen-induced (phytohaemagglutinin, concanavalin A, pokeweed mitogen, lipopolysaccharide and protein A) blastogenesis of normal bovine lymphocytes. By contrast, antibody-dependent, and spontaneous cell-mediated cytotoxicity were suppressed by only a few sera. The antibody titer against bovine leukaemia virus in these sera correlated with the percent inhibition of lymphocyte blastogenesis. These leukotic sera had no direct cellular cytotoxicity and the inhibitory activity was not lost by dialysis or heat inactivation at 62 degrees C for 30 min. However, the activity was reduced by heating at 80 degrees C for 30 min. Neither the concanavalin A sepharose 4B effluent fraction nor 3.5% polyethyleneglycol-treated serum was found to contain significant lymphocyte-inhibitory activity. Blastogenic transformation of lymphocytes prepared from leukaemic cattle was hardly detectable; however, the mitogen responsiveness of these lymphocytes was improved by a 37 degrees C 1-h preincubation followed by washing.