Is interleukin 2 necessary for the autocrine proliferation of Theileria-infected bovine cells?

Abstract

Theileria-infected bovine lymphoblastoid cells are induced to proliferate permanently such that the division of the parasites and that of their host cells occur synchronously. The mechanism by which the parasites induce the transformation of their host cells is unknown. We investigated the growth-factor dependency of a number of Theileria-infected cell lines. Supernatants of the majority of the cell lines tested in our study showed no growth-enhancing activity. However, supernatants of a limited number of cell lines occasionally enhanced the growth of parasitized cells that were used as responder cells. Thus, they contained a growth factor whose biological effect was not eliminated by an anti-interleukin-2 (anti-IL-2) antibody. Moreover, neither the proliferation of T. parva-infected cells nor that of T. annulata-infected cells was impaired by this antibody. In contrast, the anti-IL-2 antibody substantially prevented bovine peripheral blood mononuclear cells from undergoing a proliferative response upon stimulation with concanavalin A (Con A). In line with these results we observed that unlike Con A-stimulated lymphocytes, the infected cell lines did not express IL-2 mRNA. Taken together, our results suggest that Theileria-infected cells do not secrete IL-2 and that IL-2 does not play an important role in the autocrine proliferation of the parasitized host cells.