Early secreted antigenic target 6 kDa protein (ESAT-6)

Early secreted antigenic target 6 kDa protein (ESAT-6) is a small, secreted protein produced by *Mycobacterium tuberculosis* and related mycobacteria. Encoded by the rv3875 gene and secreted via the ESX-1/type VII secretion system, ESAT-6 is essential for mycobacterial virulence: it manipulates host immune responses, promotes bacterial survival, induces strong T cell responses, and stimulates cytokine production (notably IL-6 and IL-8) through diverse signaling pathways including STAT3, PKC, MAPKs, and ROS production. ESAT-6, together with its dimerization partner CFP-10, is excluded from the BCG vaccine strain, and its absence is partially responsible for the attenuation of BCG. In clinical practice, ESAT-6 is a critical antigen in immunological assays for tuberculosis diagnosis such as the QuantiFERON-TB Gold test. Its strong immunogenicity makes it a candidate for TB vaccine development, but its direct involvement in promoting tissue damage and chronic inflammation necessitates caution in therapeutic applications.

Other names

EsxAEarly secreted antigenic target of 6 kDa6 kDa early secretory antigenic targetESAT-6 protein, Mycobacterium tuberculosis

Host immune recognition: Serves as a key antigen recognized by T cells to trigger the immune system. It induces cytokine production in macrophages and epithelial cells, notably IL-6 via STAT3 activation, and IL-8 via ROS, PKC, and MAPK signaling pathway activation.