Inhibition of human monocyte-to-dendritic cell differentiation by ESAT-6 protein of Mycobacterium tuberculosis

Rahila Qureshi, Akshay Manikoth, Sangita Mukhopadhyay

Centre for DNA Fingerprinting & Diagnostics

Mycobacterium tuberculosis (Mtb) has evolved multiple strategies to evade host immune responses, enabling long-term persistence within infected hosts. One important mechanism involves interference with antigen presentation, which is essential for initiating effective adaptive immunity. Dendritic cells (DCs) are professional antigen-presenting cells that link innate and adaptive immune responses by activating naïve T cells. Disruption of DC differentiation or function can therefore severely compromise host defense against Mtb. In this study, we investigated the role of the mycobacterial virulence factor ESAT-6 (Early Secreted Antigenic Target of 6 kDa) in the differentiation of human monocytes into dendritic cells. We demonstrate that ESAT-6 significantly inhibits monocyte-to-DC differentiation, as indicated by reduced expression of DC surface markers CD209 and CD1a. In addition, ESAT-6 diminished expression of the costimulatory molecules HLA-DR and CD86. ESAT-6 treatment resulted in elevated levels of the immunomodulatory cytokines IL-6 and IL-10, however, neutralization of these cytokines failed to restore DC differentiation, indicating cytokine-independent inhibition. Mechanistic analysis revealed that ESAT-6 suppresses phosphorylation of the NF-κB p65 subunit, identifying impaired NF-κB signaling as a central mechanism underlying defective DC differentiation. This inhibitory activity was dependent on the last six amino acids of the ESAT-6 C-terminal domain. Functionally, ESAT-6-treated cells displayed a reduced capacity to prime T cells, highlighting impaired antigen-presenting function. Collectively, these findings reveal an immune evasion mechanism by which Mtb impairs dendritic cell development and function, limiting antigen presentation and T-cell priming and contributing to subversion of host adaptive immune responses during infection.