Free exopolysaccharide from [i]Mycoplasma mycoides[/i] subsp [i]mycoides[/i] possesses anti-inflammatory properties

Abstract

In this study we explored the immunomodulatory properties of highly purified free galactan, the soluble exopolysaccharide secreted by [i]Mycoplasma mycoides[/i] subsp. [i]mycoides[/i] (Mmm). Galactan was shown to bind to TLR2 but not TLR4 using HEK293 reporter cells and to induce the production of the anti-inflammatory cytokine IL-10 in bovine macrophages, whereas low IL-12p40 and no TNF-alpha, both pro-inflammatory cytokines, were induced in these cells. In addition, pre-treatment of macrophages with galactan substantially reduced lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines TNF- and IL-12p40 while increasing LPS-induced secretion of immunosuppressive IL-10. Also, galactan did not activate naive lymphocytes and induced only low production of the Th1 cytokine IFN-gamma in Mmm-experienced lymphocytes. Finally, galactan triggered weak recall proliferation of CD4+ T lymphocytes from contagious bovine pleuropneumonia-infected animals despite having a positive effect on the expression of co-stimulatory molecules on macrophages. All together, these results suggest that galactan possesses anti-inflammatory properties and potentially provides Mmm with a mechanism to evade host innate and adaptive cell-mediated immune responses