The presence of a galactosamine substituent on the arabinogalactan of Mycobacterium tuberculosis abrogates full maturation of human peripheral blood monocyte-derived dendritic cells and increases secretion of IL-10

Abstract

SUMMARY Slow-growing and pathogenic Mycobacterium spp. are characterized by the presence of galactosamine (GalN) that modifies the interior branched arabinosyl residues of the arabinogalactan (AG) that is a major heteropolysaccharide cell wall component. The availability of null mutants of the polyprenyl-phospho-N-acetylgalactosaminyl synthase (Rv3631, PpgS) and the (N-acetyl-) galactosaminyl transferase (Rv3779) of Mycobacterium tuberculosis (Mtb) has provided a means to elucidate the role of the GalN substituent of AG in terms of host-pathogen interactions. Comparisons of treating human peripheral blood monocyte-derived dendritic cells (hPMC-DCs) with wild-type, Rv3631 and Rv3779 mutant strains of Mtb revealed increased expression of DC maturation markers, decreased affinity for a soluble DC-SIGN probe, reduced IL-10 secretion and increased TLR-2-mediated NF-κB activation among GalN-deficient Mtb strains compared to GalN-producing strains. Analysis of surface expression of a panel of defined or putative DC-SIGN ligands on both WT strains or either Rv3631 or Rv3779 mutant did not show significant differences suggesting that the role of the GalN substituent of AG may be to modulate access of the bacilli to immunologically-relevant receptor domains on DCs or contribute to higher ordered pathogen associated molecular pattern (PAMP)/pattern recognition receptor (PRR) interactions rather than the GalN-AG components having a direct immunological effect per se.

A protocol for culturing environmental strains of the Buruli ulcer agent, Mycobacterium ulcerans

“…N-acetyl galactosamine has been recognized as a minor covalently-bound amino sugar component of the cell wall of some slow-growing mycobacteria and orthologs of polyprenyl-phospho-N-acetyl-galactosaminyl synthase (ppgS), which are found in the genomes of slowly-growing mycobacteria including M. bovis , M. bovis BCG, M. leprae , M. marinum and M. avium subsp. paratuberculosis , as well as in M. abscessus ; but not in the genomes of other rapidly growing Mycobacterium species such as Mycobacterium smegmatis 44 , 45 .…”

Disruption of the SucT acyltransferase in Mycobacterium smegmatis abrogates succinylation of cell envelope polysaccharides

“…1). Studies from our laboratory have shed light on the biosynthetic origin of this substituent (13) and begun to elucidate its contribution to modulation of the host immune response (14). Interestingly, succinate groups were found to substitute the same positions of the arabinan domain as well as quantitatively minor ␣-1,5-Araf positions of AG from M. tuberculosis and Mycobacterium smegmatis (15), the internal ␣-3,5-branched Araf residues of the arabinan domain of LAM from M. bovis Bacillus Calmette-Guerin (BCG) (16), and possibly the same positions of LAM from M. leprae and M. tuberculosis (17)(18)(19)(20)(21).…”

Sensing of mycobacterial arabinogalactan by galectin‐9 exacerbates mycobacterial infection

“…B-E qPCR analysis of Mmps including Mmp9 (B), Mmp10 (C), Mmp12 (D), and Mmp13 (E) from mouse peritoneal macrophages isolated from either wild-type or Galectin-9 KO mice stimulated with AG (1 lg/ml) for 24 h. (Esin et al, 2013). Moreover, the presence of a galactosamine substituent in the AG of Mtb has been found to abrogate the full maturation of human peripheral blood monocyte-derived DCs (Wheat et al, 2015). Here, we demonstrate that in vivo administration of AG causes pathological impairments in the lung, while AG-specific aptamers alleviated Mtb-induced lung injury and moderately extended survival of Mtb-infected SCID mice or M. marinuminfected zebrafish.…”