Macrophage‐mediated cytostasis and lymphocyte cytotoxicity in cattle immunized with Theileria annulata sporozoites or macroschizont‐infected cell lines

Abstract

Summary Immunization with either sporozoites or macroschizont‐infected cell lines protected calves against challenge with lethal doses of sporozoites of Theileria annulata. Stocks from India, Turkey and Morocco all conferred protective immunity to each other, irrespective of the immunizing regime. Although heterogeneous clinical responses were induced by the two immunizing regimes, both stimulated similar patterns of macrophage cytostasis as expressed as an inhibition of proliferation of macroschizont‐infected cell lines. Macrophage cytostasis was detected consistently after immunization and after challenge, arising at the same time as macroschizonts were detectable. Its expression was sustained and inhibited the proliferation of both autologous and allogeneic (BoLA‐mismatched) cell lines. In contrast, these two immunizing regimes differed in their ability to stimulate the production of cytoloxic cells. Calves immunized with autologous cell lines or sporozoites developed very transient populations of cytotoxic cells expressing only a low level of specific lysis for autologous infected cells; agglutinating antibodies for immunizing or autologous cell lines were not detected in these calves. Calves immunized with aliogeneic cell lines produced cytotoxic cells which were specific only for the immunizing cell lines; these calves also produced antibodies which agglutinated the immunizing cell lines.