ESAT-6 a Major Virulence Factor of Mycobacterium tuberculosis and a Target for New Therapeutic Interventions

Abstract

Mycobacterium tuberculosis (Mtb) the causative agent of human tuberculosis (TB) is one of the most successfully adapted-human pathogens. Human-to-human transmission occurs at high rates through aerosols containing bacteria, but the pathogen evolved prior to the establishment of crowded populations. Mtb has developed a particular strategy to ensure persistence in the host until an opportunity for transmission arise. It has refined its lifestyle to obviate the need for virulence factors such as capsules, flagella, pilli, or toxins to circumvent mucosal barriers. Instead, the pathogen uses host macrophages, where it establishes intracellular niches, for its migration into the lung parenchyma and other tissues and for the induction of long-lived latency in granulomas. Finally, at the end of the infection cycle Mtb induces necrotic cell death of macrophages to escape to extracellular milieu and instructs a strong inflammatory response required for progression from latency to disease and transmission. Common to all these events is ESAT-6, one of the major virulence factors secreted by the pathogen. This review highlights the recent advances in understanding the role of ESAT-6 in hijacking macrophage function to establish a successful infection and transmission and its use as a target for the development of diagnostic tools, and vaccines.