6 kDa early secretory antigenic target (ESAT-6) (ESAT-6)

The 6 kDa Early Secretory Antigenic Target (ESAT-6), also known as EsxA, is a critical virulence factor and potent T-cell antigen produced by Mycobacterium tuberculosis [3, 4]. It is secreted via the ESX-1 (Type VII) secretion system, typically forming a stable 1:1 heterodimer with Culture Filtrate Protein 10 (CFP-10) [5, 6]. Biologically, ESAT-6 acts as a pore-forming toxin that facilitates the rupture of host phagosomal membranes, allowing the bacteria to escape into the cytosol and evade lysosomal destruction [5, 11]. It further modulates the host immune response by binding to receptors like TLR2 and beta-2-microglobulin, leading to impaired antigen presentation and dysregulated cytokine production [7, 17]. ESAT-6 is a cornerstone of modern tuberculosis diagnostics, such as Interferon-Gamma Release Assays (IGRAs), because it is present in virulent strains but absent in the BCG vaccine strain, enabling differentiation between vaccination and infection [10, 14]. Beyond diagnostics, it is a primary candidate for novel subunit vaccines and a target for experimental anti-virulence drugs designed to disrupt its interaction with CFP-10 or inhibit its membrane-disrupting activity [16, 18].

Other names

EsxARv3875Early secretory antigenic target 6 kDa protein6 kDa early secreted antigenic targetESAT6

Induction of antigen-specific Th1 and Th17 cellular immune responses (vaccines); Detection of interferon-gamma (IFN-γ) release from sensitized T-cells upon exposure to target antigens (diagnostics); Inhibition of bacterial virulence by blocking protein-protein interactions with CFP-10 or preventing pore-mediated phagosomal escape (experimental inhibitors).