Induces apoptosis of host cells via activation of NF-kappa-B. Forms a tight 1:1 complex with EsxU (PubMed:20085764, PubMed:29559126). Complex formation results in induction of alpha-helical conformation and stability against chemical denaturation (PubMed:29559126). Probably secreted via the ESX-4 / type VII secretion system (T7SS). Actively produced during the active phase of tuberculosis. Elicits strong humoral responses. Induces significant lymphocyte proliferation and up-regulates the induction of TNF-alpha and IL-6 in tuberculosis patients. Belongs to the WXG100 family. ESAT-6 subfamily.