Responses of Bovine WC1 super(+) [gamma][delta] T Cells to Protein and Nonprotein Antigens of Mycobacterium bovis

WC1 super(+) [gamma][delta] T cells of Mycobacterium bovis-infected cattle are highly responsive to M. bovis sonic extract (MBSE). In mycobacterial infections of other species, [gamma][delta] T cells have been shown to respond to protein and nonprotein antigens, but the bovine WC1 super(+) [gamma][delta] T- cell antigenic targets within MBSE require further definition in terms of the dominance of protein versus nonprotein components. The present study sought to characterize the WC1 super(+) [gamma][delta] T-cell antigenic targets, together with the role of interleukin-2 (IL-2), in the context of M. bovis infection. This was achieved by testing crude and defined antigens to assess protein versus nonprotein recognition by WC1 super(+) [gamma][delta] T cells in comparison with CD4 super(+) [alpha] beta T cells. Both cell types proliferated strongly in response to MBSE, with CD4 super(+) T cells being the major producers of gamma interferon (IFN- [gamma]). However, enzymatic digestion of the protein in MBSE removed its ability to stimulate CD4 super(+) T-cell responses, whereas some WC1 super(+) [gamma][delta] T-cell proliferation remained. The most antigenic protein inducing proliferation and IFN-[gamma] secretion in WC1 super(+) [gamma][delta] T- cell cultures was found to be ESAT-6, which is a potential novel diagnostic reagent and vaccine candidate. In addition, WC1 super(+) [gamma][delta] T-cell proliferation was observed in response to stimulation with prenyl pyrophosphate antigens (isopentenyl pyrophosphate and monomethyl phosphate). High levels of cellular activation (CD25 expression) resulted from MBSE stimulation of WC1 super(+) [gamma][delta] T cells from infected animals. A similar degree of activation was induced by IL-2 alone, but for WC1 super(+) [gamma][delta] T-cell division IL-2 was found to act only as a costimulatory signal, enhancing antigen-driven responses. Overall, the data indicate that protein antigens are important stimulators of WC1 super(+) [gamma][delta] T-cell proliferation and IFN-[gamma] secretion in M. bovis infection, with nonprotein antigens inducing significant proliferation. These findings have important implications for diagnostic and vaccine development.