Proliferative responses of peripheral blood leucocytes of sheep infected with Trypanosoma evansi.

The effects of Trypanosoma evansi on the proliferative responses of ovine peripheral blood leucocytes (PBL) were examined in in vitro cell culture systems. Sheep were vaccinated against pneumonic pasteurellosis with a monovalent Pasteurella haemolytica vaccine and then infected with T. evansi TREU 2143. From 1 week post-infection (p.i.), the PBL were separated and stimulated in cultures with either Concanavalin A (Con A), bacterial lipopolysaccharide (LPS), pasteurella antigen (P.ag), or homologous trypanosome antigen (T.ag). The proliferative responses of the cells to Con A and LPS were significantly (P < 0.001) suppressed by the infection. This suppression was associated with active infection, as treatment of the sheep with a trypanocide restored the proliferative ability of the cells to both mitogens. Similarly, active infection significantly (P < 0.001) suppressed specific responses to P.ag and T.ag but although treatment resulted in full specific proliferative responsiveness to the homologous trypanosome antigen, the same was not true of P.ag, in which the responsiveness of cells from uninfected vaccinated sheep to it were still significantly higher (P < 0.001) than those of cells from infected sheep.