Pollen allergens do not come alone: Pollen associated lipid mediators (PALMS) shift the human immue systems towards a T_H2-dominated response

Pollen allergy is characterized by a TH2-biased immune response to pollen-derived allergens. However, pollen-exposed epithelia do not encounter pure allergen but rather a plethora of protein and non-protein substances. We demonstrated that pollen liberate lipids with chemical and functional similarities to leukotriens and prostaglandins - the pollen associated lipid mediators (PALMs). To date, two main groups of PALMs have been characterized: The immunostimulatory PALMs activating innate immune cells such as neutrophils and eosinophils, and the immunomodulatory E1-phytoprostanes blocking IL-12 production of dendritic cells, resulting in the preferential induction of TH2 responses. This article reviews our work in the field of PALMs and their effects on cells of the innate and adoptive immune system. From recent results a general picture starts to emerge in which PALMs (and possibly other pollen-associated substances) may - independently from protein allergens - propagate an overall TH2 favoring micromilieu in pollen exposed tissue of predisposed individuals.