Immunomodulating effects of lichen-derived polysaccharides on monocyte-derived dendritic cells

Many naturally occurring polysaccharides from fungi and lichens have been found to have immunomodulating activity. However, the majority of these studies have focused on their effects on the innate arm of the immune system. Although dendritic cells (DCs) belong to the innate immune system, they play an important role as a bridge between the innate and the adaptive immune response. In this study, the effects of 11 chromatographically purified and well-characterised lichen polysaccharides (of different structural types) on the maturation of DCs were tested by analysing the secretion of IL-12p40 and IL-10 by human monocyte-derived dendritic cells in vitro. Four of the polysaccharides upregulated IL-10 secretion by the dendritic cells, as compared with unstimulated cells, the beta-glucans lichenan and Ths-2 and the heteroglycans Pc-4 and thamnolan. IL-12p40 secretion was significantly upregulated by the beta-glucan lichenan and the heteroglycans Pc-2, Pc-4, thamnolan and Ths-4, while the mature dendritic cells stimulated with the heteroglycan Pc-1 secreted significantly less IL-12p40 than the unstimulated cells. Proportional index (PI) was used to determine the relationship between the IL-12p40 and IL-10 secretion. The PI of all the beta-glucans, i.e. lichenan, pustulan and Ths-2, and the heteroglycan thamnolan was significantly lower than the PI observed for the unstimulated cells, which was mainly due to increased IL-10 secretion. Therefore, these polysaccharides could be considered suitable candidates in tolerance and anti-inflammatory studies, as IL-10 is one of the major cytokines involved in tolerance and anti-inflammatory responses.