Pollen-assoziierte lipidmediatoren (PALMs)

We recently demonstrated that pollen are fare more than allergen carriers releasing bioactive lipid mediators (pollen associated lipid mediators - PALMs) upon contact with an aqueous phase. These mediators released by pollen (birch and grass) activate and recruit PMN in vitro. Pollen derived granulocytic chemotactic activity may be attributable to one or more lipids that are functionally and structurally closely related to leukotriens. Pollen-extracts contained substantial amounts of linolenic acid-derived hydroxy fatty acid derivatives namely 13-HODE and 13-HOTE which also lead to activation and migration of PMN. Apart from these proinflammatory substances also immunmodulatory lipid mediators were identified. This immunmodulatory activity was shown by a block of the LPS/CD40-induced IL-12 p70 production in human monocyte derived dendritic cells leading also to an enhanced ensuing Th2-response. The chemical analysis revealed substantial amounts of the recently described phytoprostanes of which the phytoprostanes E ₁ could be identified as one of the IL-12 reducing factors in aqueous pollen extracts. These results suggest that pollen derived lipid mediators play an important role in the modulation of dendritic cell function, and consequently in the nature of the corresponding T cell response.