SECRETION OF COSTIMULATORY 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 f or their capacity to secrete co-stimulatory cytokines. To this end, th e culture medium was titrated on suboptimally stimulated murine thymoc ytes. A low residual release by normal monocytes was noted which usual ly 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 Trypanos oma congolense, the cells released high titres spontaneously. This inc rease in co-stimulatory cytokine secretion was noted in both periphera l blood monocytes and splenic macrophages and was amplified by additio n of indomethacin. The activation was transient, and the titres had dr opped to pre-infection values at the end of the experiment. At that ti me, the monocytes were, however, still able to respond to external sti muli. Addition of neutralizing anti-transforming growth factor beta an tibodies did not influence the thymocyte co-stimulatory activity of th e supernatants. High levels of co-stimulatory cytokine secretion were noted with monocytes from both the susceptible Boran breed and the tol erant N'Dama breed. Early in infection, at Day 10 post infection, the production by the N'Dama monocytes was 16 times higher than the produc tion by the Boran monocytes. Later in the infection, the titres were s imilar in both breeds.