BCG infection in M0 macrophages activated TLR2-MyD88 and Mincle-CARD9 signaling pathways, stimulating nitric oxide (NO) production and enhanced killing of LVS.
In contrast, avirulent mycobacteria were effectively killed by inducing the Toll-like receptor 2/4 (TLR2/4) pathway-dependent expression of cathelicidin, while small interfering RNA (siRNA)-mediated cathelicidin silencing increased the survival of <i>M. bovis</i> BCG in BM-MSCs.We also showed that <i>M. bovis</i> BCG infection caused increased expression levels of MyD88, phospho-interleukin-1 receptor-associated kinase 4 (pIRAK-4), and the p38 mitogen-activated protein kinase (MAPK) signaling pathway.
Compared with the control group, miR-21 expression and levels of TNF-a, IL-6 and IL-10, as well as cell apoptosis and necrosis rates, were elevated, while expression of TLR4 and MyD88, as well as cell viability, were reduced in BCG infection groups.
More importantly, overexpression of miR-149 in RAW264.7 cells was associated with a significant decrease of MyD88 protein expression, as well as a reduced production of inflammatory mediator NF-κB 1, TNF-α and IL-6 in response to BCG infection or LPS stimulation.
Moreover, the abundance of miR-124 transcript in murine AMs of MyD88 deficient mice is significantly less than that of their wild-type or heterozygous littermates; and the BCG infection fails to induce miR-124 expression in the lung of MyD88 deficient mouse.