Adjuvant activity of intact pollen

To understand the unique properties of respiratory allergens in initiating and sustaining the allergic inflammation, we have examined the adjuvant effect of intact pollen grains on dendritic cells (DCs). Human monocyte-derived DCs were cultured with intact grains of grass pollen for 48 h. The state of DC's maturation was analyzed by FACS and their cytokine production by ELISA. T-cell priming activity of DCs was examined in co-cultures with naïve CD4 +T cells. Grass pollen up-regulated the expression of the co-stimulatory and accessory molecules, CD86, CD83, CD80, HLA-DR, CD40, CD54, on immature DCs. Pollen promoted up-regulation of CC chemokine receptor 7 and interestingly CCR5 as well. Cytokine profile of these DCs exposed to pollen was not affected significantly. Immature DCs exposed for 48h to pollen stimulated the proliferation of naïve CD4+ T cells more efficiently than untreated DCs. These CD4+ T cells, primed with pollen-exposed DCs, produced upon stimulation significantly higher amounts of IL-5, IL-13, IL-4 and IL10. Intact grains of pollen induce activation and maturation of DCs in vitro. Similar mechanisms may be effective in vivo, suggesting that pollen acts as an adjuvant in the elicitation phase of allergic reactions.