Mycobacterium tuberculosis EsxL induces TNF-α secretion through activation of TLR2 dependent MAPK and NF-κB pathways

Mycobacterium tuberculosis (Mtb) employs distinct strategies to circumvent host immune responses during the infection process. Various Mtb cell-wall associated and secretory proteins are known to play a critical role in the orchestration of host innate immune responses through modulation of signaling pathways. Mtb genome encodes for 23 (EsxA-EsxW) proteins belonging to the ESAT-6 like family; however, most of them are functionally unknown. Here, we show that Mtb EsxL induces tumor necrosis factor-alpha (TNF-α) production by activating nuclear translocation of nuclear factor-κB (NF-κB) via interaction with Toll-like Receptor 2 (TLR2). Blocking or silencing of TLR2 abrogated nuclear translocation of NF-kB and TNF-α production. Treatment with recombinant purified EsxL (rEsxL) activated mitogen-activated protein kinase (MAPK) pathway by inducing the phosphorylation of extracellular signal-regulated kinase (ERK) and p38 kinase (p38) pathways. At the same time, inhibition of ERK and p38 down-regulated the expression of TNF-α in rEsxL exposed murine macrophages. Besides TNF-α, EsxL also induced the production of IL-6 proinflammatory cytokine. Taken together, these results suggest that EsxL is able to induce TNF-α secretion via TLR2 through activation of NF-κB and MAPK signaling. This study will help in deducing therapeutic strategies for better control of the disease.