A secreted protein. Acts as a strong host (human) T-cell antigen (PubMed:11940590). Involved in translocation of bacteria from the host (human) phagolysosome to the host cytoplasm (PubMed:17604718). Might serve as a chaperone to prevent uncontrolled membrane lysis by its partner EsxA; native protein binds poorly to artificial liposomes in the absence or presence of EsxA (PubMed:17557817, PubMed:26260636). EsxA and EsxA-EsxB are cytotoxic to pneumocytes (PubMed:19906174). EsxB (and EsxA-EsxB but not EsxA alone) activates human neutrophils; EsxB transiently induces host (human) intracellular Ca(2+) mobility in a dose-dependent manner, monocytes and lymphocytes do not respond (PubMed:25332123). Neutrophils respond to EsxB by chemotaxis and primed neutrophils treated with EsxB produce reactive oxygen species (ROS); Ca(2+) release and the ROS burst via are induced by an unidentified G-protein coupled receptor (PubMed:25332123). May help regulate assembly and function of the type VII secretion system (T7SS) (PubMed:25865481). Able to form a homodimer (By similarity). Forms a tight 1:1 complex with EsxA (ESAT-6) (PubMed:11940590, PubMed:14557536, PubMed:16048998, PubMed:16973880, PubMed:19854905, PubMed:19906174, PubMed:23150662, PubMed:26260636, PubMed:20085764, PubMed:15973432, PubMed:24586681). The complex persists even after secretion (PubMed:16048998). In vitro EsxB only interacts with non-acetylated EsxA; it interacts with C-terminally truncated EsxA (missing the last 10 residues) (PubMed:15378760). The native EsxA-EsxB complex dissociates at pH 4.0, and EsxA may then be freed to then lyse membranes (PubMed:17557817). Another study using recombinant protein did not find dissociation at acidic pH (PubMed:23150662). Recombinant heterodimer (with a His tag on EsxB) can be dissociated by the detergents amidosulfobetaine-14 and lauryldimethylamine N-oxide (PubMed:26260636). Interacts with EccCb1 (PubMed:14557536, PubMed:16973880, PubMed:25865481). Interacts with PPE68 (PubMed:17433643). Interacts with EccCa1, EccCb1, EsxA, EspI and EspJ (PubMed:19854905). An artificial EsxB-EsxA heterodimer interacts with EspA, EccB1, EccCa1, EccCb1, EspI, EspJ, EccA2 and EccE2; the latter 2 are from the adjacent ESX-2 locus (PubMed:19854905). Interacts with host (human) beta-2-microglobulin (B2M) in complex with EsxA; only binds free B2M and not B2M in complex with HLA-I (PubMed:25356553). Probably secreted via the ESX-1 / type VII secretion system (T7SS) (PubMed:19876390). Binds to CD14+ and CD19+ host (human) cells (PubMed:19265145). Localized on the cell surface of host (human) cell monocytes and macrophages (often in patches), but not fibroblasts (PubMed:15973432). Exogenous EsxA and EsxA-EsxB complex can enter host (human and mouse) endoplasmic reticulum (PubMed:25356553). Constitutively expressed, part of the esxB-esxA operon (PubMed:9846755). May be secreted as a 4 coiled-coil complex with EsxA (PubMed:16048998). The C-terminal domain is required for interaction with both EsxA and EccCb1; the last 7 amino acids are necessary and sufficient for EccCb1 binding and secretion (PubMed:16973880). Bacteria no longer translocate from the phagolysosome to the cytosol of host (human) cells probably due to polar effects on the downstream esxA gene; bacteria replicate in phagolysosome, decreased apoptosis of infected host (human) dendritic cells (PubMed:17604718). Loss of ability to lyse host (human) lung epithelial cells, possibly due to polar effects on the downstream esxA gene; in BALB/c-infected mice bacteria are not as invasive and cause decreased lung disease (PubMed:14557547). No growth in the human macrophage-like cell line THP-1, no cytotoxicity (PubMed:14756778). Inactivation leads to absence of EsxA and EsxB from cell lysates (PubMed:14756778, PubMed:16368961). No secretion of EspA (PubMed:16030141). Genes esxA and esxB are part of RD1 (part of a 15-gene locus known as ESX-1), a section of DNA deleted in the M.bovis BCG strain used for vaccination. Deletion of this region is thought to be largely responsible for the attenuation of BCG, and esxA and EsxB in particular are quite important in this effect (PubMed:14557547, PubMed:14756778, PubMed:16368961). Secretion of EspA, EsxA and EsxB is mutually dependent (PubMed:16030141). To improve expression in E.coli the proteins were cloned as a single protein in the order esxB-esxA with a cleavable thrombin tag (PubMed:19854905). Belongs to the WXG100 family. CFP-10 subfamily.