Secretion of co-stimulatory cytokines by monocytes and macrophages during infection with Trypanosoma (Nannomonas) congolense in susceptible and tolerant cattle.

Bovine macrophages and monocytes were cultured in vitro and analyzed for their capacity to secrete co-stimulatory cytokines. To this end, the culture medium was titrated on suboptimally stimulated murine thymocytes. A low residual release by normal monocytes was noted which usually remained below the detection limit of the assay. These cells could be induced to secrete high titres following activation with bacterial lipopolysaccharide. When harvested from animals infected with Trypanosoma congolense, the cells released high titres spontaneously. This increase in co-stimulatory cytokine secretion was noted in both peripheral blood monocytes and splenic macrophages and was amplified by addition of indomethacin. The activation was transient, and the titres had dropped to pre-infection values at the end of the experiment. At that time, the monocytes were, however, still able to respond to external stimuli. Addition of neutralizing anti-transforming growth factor beta antibodies did not influence the thymocyte co-stimulatory activity of the supernatants. High levels of co-stimulatory cytokine secretion were noted with monocytes from both the susceptible Boran breed and the tolerant N'Dama breed. Early in infection, at Day 10 post infection, the production by the N'Dama monocytes was 16 times higher than the production by the Boran monocytes. Later in the infection, the titres were similar in both breeds.