**4. Use of CFP10 and ESAT6 as tools for diagnosis and vaccine**

CFP-10 and ESAT-6 were identified in a screen to identify the proteins present in culture filtrates of Mtb and *M. bovis BCG*, which could induce T cell mediated response. (Andersen et al., 1991a; Andersen et al., 1991b; Andersen et al., 1994; Weldingh et al., 1998; Weldingh et al., 1999). The screen yielded six low molecular weight antigens *viz*. Rv3871, Rv3872, Rv3873, CFP-10, ESAT-6 and Rv3878. These antigens when expressed and purified as recombinant proteins gave strong humoral response in tuberculous guinea pigs while only two antigens i.e. CFP-10 and ESAT-6 showed strong delayed type hypersensitivity (DTH) reaction in the guinea pigs (Weldingh et al., 1999). CFP10 and ESAT6 are potent T cell antigens and induce strong T cell response. In mice infected with Mtb, CFP-10 specific T cells were observed at quite early stage of infection in lungs. These T cells were activated by CFP-10 epitopes and were recruited in large numbers (Kamath et al., 2004). This resulted in production of large amounts of interferon- (IFN-). Recombinant CFP-10 has also been shown to be a potent T cell antigen, inducing T cell proliferation and IFN- production in peripheral blood mononuclear cells in about 70% of purified protein derivative (PPD) positive asymptomatic individuals. CFP-10 was also shown to induce delayed type hypersensitivity (DTH) in Mtb infected guinea pigs but not in *M. bovis* BCG infected guinea pigs (Colangeli et al., 2000). ESAT-6 is also a RD-1 antigen inducing robust levels of IFN- by T cells in early stages of *M. tuberculosis* infection (Porsa et al., 2006; Ravn et al., 1999; Skjot et al., 2000; de Jong et al., 2006). Two different T cell epitopes were observed in mice, which were recognized by different MHCII molecules under different circumstances (Dietrich et al., 2005).
