TRANSGLUTAMINASE OF POLLENS WITH DIFFERENT ALLERGENIC POTENTIAL IS DIFFERENTLY AFFECTED BY METEOROLOGICAL AND POLLUTANT CONDITIONS

A dramatic increase in prevalence and severity of respiratory allergic diseases in recent years (hay fever, bronchial asthma, seasonal allergic conjunctivitis) is reported by several authors, among which Cecchi et al., 2010. Human activities are resulting in changes in global climate, which in turn have a negative impact on human health. An important example is provided by the influence of climate changes on respiratory diseases triggered by biological aerosol carrying antigenic proteins such as those of pollen grains. Pollen allergenicity is frequently used to study the interrelationship between air pollution and respiratory allergy. Although the link between climate change and/or pollution and increasing allergenic potential of pollen is proven, the underlying mechanism is little understood. Apple (Malus) fruit allergies are mainly due to four different classes of allergens: Mal d 1, 2, 3, 4, but little is known on the expression of allergens also in apple pollen, whose allergenicity is poor, perhaps because dispersed by insects. Here we have investigated the presence of Mal d isoallergens also in pollen using a RT-PCR approach both on ungerminated and germinated pollen. In Corylus (hazelnut) fruit various allergens are reported to be responsible for severe allergic food diseases, but in this case, also pollen is well documented as an allergenic source. We used models mimicking climate and pollution conditions to study vitality and germinability of both pollens. In respect to the natural conditions, changes in temperature, humidity and some pollutants, such as acid rains and copper, alone or in combination, have a negative effect on viability and germination of both types pollen, especially Corylus, and morphological observations showed that the pollen grains are damaged. This can cause a release also of allergens. In addition to the data in literature on the effect of climate changes on the production of more pollen and its allergenes, it is possible that the allergene molecule itself could be modified magnifying its peculiar properties. Transglutaminases (TGases), able to post-translationally modify proteins, have been found recently also in pollen (Serafini-Fracassini et al., 2009). These enzymes play a role on the onset of specific pathologies and associated autoimmune inflammatory conditions (Lorand and Graham, 2003). TGase activity is increased following cellular stresses of different origins (Verderio et al., 2005). In mammalian cells, the intracellular tTGase, is rapidly secreted, following cell insult, into the extracellular environment, where it plays a key role in cell survival (Verderio et al., 2005). We reported that pollen TGase, necessary to allow the apple pollen germination, is released in the pollen cell wall and in the extracellular medium where also polyamines are released (Di Sandro et al., 2010). Its role is still under study, but a relationship between extracellular pollen TGase and the modification of pollen allergens, if co-localised, could be hypothesised. Moreover the pollen TGase activity might be affected by stress conditions such as those caused by environmental changes or pollution. We observed that TGase expression as well as its Ca2+-dependent activity in the two different species of pollen increase in a very remarkable way when pollens are exposed to stressful conditions, especially high humidity, mainly in Corylus, which in addition is particularly affected by pollution. Probably, climate change induce an alteration or damage to pollen cell wall that causes the pollen grains to release their content in the medium, including TGase enzyme, as confirmed by the observed TGase immuno-localization and by the in situ activity assay data, in addition to FITC-cadaverine conjugation.