Functional and Phenotypic Characterization of WC1+ γ/δ T Cells Isolated from Babesia bovis-Stimulated T Cell Lines

Functional studies with WC1+ γ/δ T cell lines were performed to clarify the role of this subpopulation of γ/δ T cells in the in vitro immune response to Babesia bovis. As CD4+ T cells decreased and γ/δ T cells increased in B. bovis -stimulated T cell lines, antigen-specific proliferation declined to background levels. One irradiated γ/δ T cell line inhibited proliferation of autologous Th1 cells, although unirradiated γ/δ T cells either synergized with or had no effect on Th cell proliferation. γ/δ T cells were not cytolytic for bovine α/β T cells, but expressed natural killer (NK)-like cytotoxicity when assayed on xenogeneic NK-sensitive target cells. The γ/δ T cells were IL-2 dependent and expressed IFN-γ and TNF-α, but not TNF-β. IL-2. or IL-4 mRNA. Together, these results raise the possibility that WC1+ γ/δ T cells respond in vitro to autoantigens present on CD4+ T cells or to cytokines secreted by activated CD4+ T cells, resulting in modulation of the CD4+ T cell response and outgrowth of the γ/δ T cells in parasite-stimulated lines.