Probable virulence factor. In mice, elicits increased levels of IFN-gamma, IL-12 and IgG(2a), indicating a dominant Th1 host immune response. Forms a tight 1:1 complex with EsxW. The complex is destabilized at low pH. Unfolding of the proteins is required for dissociation of the complex and membrane binding. Probably secreted via the ESX-5 / type VII secretion system (T7SS) (Probable). May bind to lipid membranes after dissociation of the complex (Probable). Potent T-cell antigen that could be a subunit vaccine candidate. Belongs to the WXG100 family. ESAT-6 subfamily.