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

Early secretory antigenic target 6 kDa (ESAT-6), also known as EsxA, is a highly immunodominant protein secreted by Mycobacterium tuberculosis that plays a pivotal role in the pathogen's virulence [UniProt: P9WNK7]. It is secreted as a 1:1 heterodimeric complex with its partner protein, CFP-10 (10 kDa culture filtrate protein), via the specialized ESX-1 (Type VII) secretion system [PubMed: 17618858]. The primary biological function of ESAT-6 is to facilitate the disruption of the host macrophage phagosomal membrane, allowing the bacteria to escape into the cytosol and promote cell-to-cell spread [PubMed: 22108155]. Additionally, ESAT-6 modulates host immunity by interacting with TLR2 and inhibiting signaling pathways such as NF-κB, thereby suppressing the host's pro-inflammatory response [PubMed: 19144317]. Because the ESAT-6 gene is located in the Region of Difference 1 (RD1) which is absent in the Mycobacterium bovis BCG vaccine strain, it is a critical target for diagnostic Interferon-Gamma Release Assays (IGRAs) like QuantiFERON-TB Gold [CDC: MMWR]. In drug development, ESAT-6 is a lead candidate for next-generation subunit vaccines (e.g., M72/AS01E) and is being investigated as a target for therapeutic antibodies designed to neutralize its cytolytic properties [PubMed: 30104648].

Other names

EsxA6 kDa early secretory antigenic targetRv3875Early soluble antigen target 6 kDa

ESAT-6 serves as a key immunodominant antigen in diagnostic assays to stimulate T-cell interferon-gamma release and as a vaccine subunit to induce protective Th1-mediated immunity. Experimental therapeutic approaches aim to neutralize its lytic activity using monoclonal antibodies to prevent phagosomal escape and bacterial spread.