Influence of climate change on the allergenicityof pollen: the involvement of pollen transglutaminase

Climatic trends resulting from increases in temperature and outdoor air pollution influence the allergenicityof pollen, which in turn is responsible for the dramatic raise in respiratory allergic diseases attributed to climate change (hay fever, bronchial asthma, seasonal allergic conjunctivitis). Although the link between climate change and pollen allergenicityis proven, the underlying mechanism is little understood. Increased pollen production and higher airway sensitization have been blamed; however the effect of climate change on the antigenicityof pollen grains has never been investigated. In mammals, type 2 transglutaminase(TG2) is implicated in autoimmune inflammatory conditions and enhances the activity of pro-inflammatory secretoryphospholipaseA2 (sPLA2) (reviewed in Verderioet al 2005). Moreover, TG2 leads to protein modifications in conditions of cell stress in mammals and plants. Recently, a Ca2+-dependent TG activity has been identified in the pollen cell wall (reviewed in Del Ducaand Fracassini2005), raising the possibility that pollen TG may have a role in pollen antigen modification and in the transamidationof proteins in the human mucosa.