ESAT-6

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ESAT-6 (Early Secreted Antigenic Target 6 kDa) is a protein encoded by the esxA gene in Mycobacterium tuberculosis, the bacterium responsible for tuberculosis (TB). ESAT-6 is a potent T-cell antigen and plays a crucial role in the pathogenesis of tuberculosis. It is one of the key components of the RD1 region (Region of Difference 1) of the Mycobacterium tuberculosis genome, which is absent in the BCG vaccine strain.

Structure and Function

ESAT-6 is a small, 6 kDa protein that forms a complex with another protein, CFP-10 (Culture Filtrate Protein 10 kDa). This complex is secreted by the Type VII secretion system (ESX-1) of Mycobacterium tuberculosis. The ESAT-6/CFP-10 complex is involved in the disruption of phagosome membranes, facilitating the escape of the bacterium into the cytosol of macrophages.

Role in Pathogenesis

ESAT-6 is a critical virulence factor for Mycobacterium tuberculosis. It contributes to the bacterium's ability to evade the host's immune system by inhibiting the maturation of phagosomes and promoting the escape of the bacterium into the cytosol. This allows Mycobacterium tuberculosis to replicate within macrophages and spread to other cells.

Diagnostic Use

ESAT-6 is used in interferon-gamma release assays (IGRAs), such as the QuantiFERON-TB Gold test, to diagnose latent tuberculosis infection (LTBI). These tests measure the release of interferon-gamma (IFN-γ) in response to ESAT-6 and CFP-10, which are absent in the BCG vaccine strain and most non-tuberculous mycobacteria, making them specific markers for Mycobacterium tuberculosis infection.

Research and Development

Ongoing research is focused on understanding the precise mechanisms by which ESAT-6 contributes to the pathogenesis of tuberculosis and exploring its potential as a target for new tuberculosis vaccines and therapeutics.

See Also

• Mycobacterium tuberculosis
• Tuberculosis
• BCG vaccine
• Interferon-gamma release assays
• CFP-10
• Type VII secretion system