PROLIFERATIVE RESPONSES OF PERIPHERAL-BLOOD LEUKOCYTES OF SHEEP INFECTED WITH TRYPANOSOMA-EVANSI

The effects of Trypanosoma evansi on the proliferative responses of ov ine peripheral blood leucocytes (PBL) were examined in in vitro cell c ulture systems. Sheep were vaccinated against pneumonic pasteurellosis with a monovalent Pasteurella haemolytica vaccine and then infected w ith T. evansi TREU 2143. From 1 week postinfection (p.i.), the PBL wer e separated and stimulated in cultures with either Concanavalin A (Con A), bacterial lipopolysaccharide (LPS), pasteurella antigen (P.ag), o r homologous trypanosome antigen (T.ag). The proliferative responses o f the cells to Con A and LPS were significantly (P < 0.001) suppressed by the infection. This suppression was associated with active infecti on, as treatment of the sheep with a trypanocide restored the prolifer ative ability of the cells to both mitogens. Similarly, active infecti on significantly (P < 0.001) suppressed specific responses to P.ag and T.ag but although treatment resulted in full specific proliferative r esponsiveness to the homologous trypanosome antigen, the same was not true of P.ag, in which the responsiveness of cells from uninfected vac cinated sheep to it were still significantly higher (P < 0.001) than t hose of cells from infected sheep.