A secreted protein. Acts as a strong host T-cell antigen. Involved in translocation of bacteria from the host (human) phagolysosome to the host cytoplasm. Might serve as a chaperone to prevent uncontrolled membrane lysis by its partner EsxA. Forms a tight 1:1 complex with EsxA (ESAT-6). Probably secreted via the ESX-1 / type VII secretion system (T7SS). Belongs to the WXG100 family. CFP-10 subfamily.