Pollen-derived low-molecular weight factors inhibit 6-sulfo LacNAc+ dendritic cells' capacity to induce T-helper type 1 responses.

Summary Background Evidence is accumulating that the pollen exsudate contains an array of non-allergenic, pro-inflammatory and immunomodulatory substances acting on the innate and adaptive immune system. In this context, pollen-associated E1-phytoprostanes (PPE1) were shown to licence human monocyte-derived dendritic cells for T-helper type 2 (Th2) polarization of naive T cells. Objective This study aims at analysing the impact of pollen-associated lipid mediators on cytokine secretion and maturation of 6-sulfo LacNAc+ dendritic cells (slanDCs), the most abundant native dendritic cell (DC) in human peripheral blood, and further dissecting the biologically active substance(s) within aqueous pollen extracts. Results Aqueous birch pollen extracts dose-dependently inhibited the lipopolysaccharide (LPS)-induced IL-12 p70 production, while the levels of IL-6 remained unaffected. PPE1 inhibited secretion of both IL-12 p70 and IL-6. Aqueous pollen extracts, but not PPE1 or F1-phytoprostanes significantly reduced the LPS-induced surface expression of the maturation markers CD80, CD83, CD40 and CCR-7, an effect that was independent of proteins and that was still present in a 3 kDa cut-off fraction of the pollen extract. These effects were observed irrespective of the atopy status of the donors. Finally, slanDCs exposed to aqueous pollen extracts were impaired in eliciting an IFN-γ response in naive CD4+ T cells. Conclusion Our data show that slanDCs, a subset of human blood DCs with constitutively high potency to induce Th1 responses, are susceptible to the Th2 polarizing effect of low molecular weight, non-protein factors derived from pollen. Cite this as: S. Gilles, D. Jacoby, C. Blume, M. J. Mueller, T. Jakob, H. Behrendt, K. Schaekel and C. Traidl-Hoffmann, Clinical & Experimental Allergy, 2010 (40) 269–278.