EsxL inhibits MHC-II expression by promoting hypermethylation in class-II transactivator loci in macrophages.

is known to modulate the host immune responses to facilitate its persistence inside the host cells. One of the key mechanisms includes repression of class-II transactivator (CIITA) and MHC-II expression in infected macrophages. However, the precise mechanism of CIITA and MHC-II down-regulation is not well studied. 6-kDa early secretory antigenic target (ESAT-6) is a known potent virulence and antigenic determinant. The genome encodes 23 such ESAT-6 family proteins. We herein report that and bacillus Calmette-Guérin infection down-regulated the expression of CIITA/MHC-II by inducing hypermethylation in histone H3 lysine 9 (H3K9me2/3). Further, we showed that ESAT-6 family protein EsxL, encoded by , is responsible for the down-regulation of CIITA/MHC-II by inducing H3K9me2/3. We further report that induced the expression of nitric-oxide synthase, NO production, and p38 MAPK pathway, which in turn was responsible for the increased H3K9me2/3 in CIITA via up-regulation of euchromatic histone-lysine -methyltransferase 2 (G9a). In contrast, inhibition of nitric-oxide synthase, p38 MAPK, and G9a abrogated H3K9me2/3, resulting in increased CIITA expression. A chromatin immunoprecipitation assay confirmed that hypermethylation at the promoter IV region of CIITA is mainly responsible for CIITA down-regulation and subsequent antigen presentation. We found that co-culture of macrophages infected with -expressing and mouse splenocytes led to down-regulation of IL-2, a key cytokine involved in T-cell proliferation. In summary, we demonstrate that EsxL inhibits antigen presentation by enhancing H3K9me2/3 at the CIITA promoter, thereby repressing its expression through NO and p38 MAPK activation.