Titration in cattle of infectivity and immunogenicity of autologous cell lines infected with Theileria parva

Abstract

Cell lines infected with Theileria parva were derived by infection of bovine peripheral blood lymphocytes with sporozoites in vitro. Cattle were inoculated with doses of autologous infected cells ranging from 1 × 10 1 to 1 × 10 8. Infection became established in animals which received 1 × 10 2 or more cells. While 1 × 10 2 cells resulted in sub-patent infection with development of immunity to challenge with sporozoites, larger doses of cells gave rise to patent infections of increasing severity. Thus, doses of 1 × 10 5 and 1 × 10 6 cells sometimes produced lethal infections and with 1 × 10 7 and 1 × 10 8 the outcome was invariably lethal. Based on the previous observation that induction of immunity by allogeneic cells requires transfer of infection into the recipient-host cells, a comparison of the infections produced by autologous and allogeneic cells indicated that the transfer of infection from allogeneic cells occurs at a frequency of maximally 1 × 10 −5. Two pairs of cattle were identified as being mutually non-reactive in the mixed leukocyte reaction (MLR). Doses of 1 × 10 6 and 1 × 10 7 cells of cell lines derived from 1 animal of each pair were inoculated into the autologous host, the non-reactive partner and an animal which was shown to be strongly reactive to the donor in the MLR. In each instance, the reaction in the MLR non-reactive recipient was not significantly different from that of the MLR reactive recipient, but was markedly different from that of the autologous recipient.