Allergies
An allergy may be a damaging immune response by the body to a substance, especially pollen, fur, a particular food, or dust, to which it has become hypersensitive.

# Theoretical allergies
Def. a "disorder of the immune system causing adverse reactions to substances (allergens) not harmful to most and marked by the body's production of histamines and associated with atopy, anaphylaxis, and asthma" is called an allergy.

# Pollen allergy in Europe
"The allergenic content of the atmosphere varies according to climate, geography and vegetation. Data on the presence and prevalence of allergenic airborne pollens, obtained from both aerobiological studies and allergological investigations, make it possible to design pollen calendars with the approximate flowering period of the plants in the sampling area."
"Aerobiological and allergological studies show that the pollen map of Europe is changing also as a result of cultural factors (for example, importation of plants such as birch and cypress for urban parklands), greater international travel (e.g. colonization by ragweed in France, northern Italy, Austria, Hungary etc.) and climate change. In this regard, the higher frequency of weather extremes, like thunderstorms, and increasing episodes of long range transport of allergenic pollen represent new challenges for researchers."
"Pollen allergy has a remarkable clinical impact all over Europe, and there is a body of evidence suggesting that the prevalence of respiratory allergic reactions induced by pollens in Europe has been on the increase in the past decades (16)."
"The prevalence of pollen allergy is presently estimated to be up 40%. Exposure to allergens represents a key factor among the environmental determinants of asthma, which include air pollution (8)."
"In Europe, the main pollination period covers about half the year, from spring to autumn, and the distribution of airborne pollen taxa of allergological interest is related to five vegetational areas":
- Arctic: birch
- Central: deciduous forest, birch, grasses
- Eastern: grasses, mugwort, ragweed
- Mountains: grasses (with a pollination season delayed by three-four weeks in comparison with areas at sea level)
- Mediterranean: Parietaria, olive trees, grasses and also cypress

# Gramineae
"The grass family (Gramineae) comprises more than 600 genera and over 10 000 species, of which more than 400 herbaceous, wind-pollinated plants are found in Europe (15). The most abundant airborne grass pollen originates from tall meadow grasses such as timothy (Phleum pratense), orchard grass (Dactylis glomerata), or meadow foxtail (Alopecurus pratensis). Cultivated rye (Secale cereale), which has remarkably high pollen production, is another potent source of allergens (16). However, with very few exceptions, all grass-pollen types show a very high degree of cross reactivity (17, 18)."
"Grass allergens induce mostly nasal and conjunctival symptoms. Djukanovic et al. (21) provided evidence that natural exposure to grass pollen may exacerbate asthma, and, so, induce an inflammatory response involving T cells, mast cells and eosinophils."

# Trees
"The most allergenic tree pollen is produced by birch (Betula) in north, central, and eastern Europe, and by Olive (Olea europaea) as also cypress (Cupressus) in the Mediterranen regions."
Fagales "comprises three families: Betulaceae, including the genera Betula (birch) and Alnus (alder); Corylaceae, including the genera Corylus (hazel), Carpinus (hornbeam), and Ostrya (hopbeam); Fagaceae, including the genera Quercus (oak), Fagus (beech), and Castanea (sweet chestnut)."
A "high cross-reactivity exists within cupressacace family (Cupressus, Juniperus and Cryptomeria) and between Cupressacae and Taxacee (5356) which have quite different pollination seasons, overlapping or preceding the cypress pollination period. This observation is of clinical importance, where cross-reacting and earlier flowering plants (C. arizonica is one of the most spread in several European areas) are well represented."

# Weeds
"Parietaria is the main allergenic genus of the Urticaceae (nettle) family.  The major allergens of both species are small glycoproteins with molecular weights ranging between 10 and 14 kDa, with high cross-reactivity (61). Recent findings showed that P judaica pollen contains an aminopeptidase which is able to disrupt epithelium barrier, enhancing the delivery of allergenic protein to dendritic cells (62)."
An "increasing body of evidence support use of sublingual specific immunotherapy for subjects with symptoms due to Parietaria pollen (74, 75)."
"The Compositae (Asteraceae), is one of the largest plant families with almost 20 000 species. Ragweed (Ambrosia) and mugwort (Artemisia) are the most involved in pollenosis"

# Pathogenetics
"In the context of allergy, pollen grains have been simply regarded as allergen carriers, and little attention has been devoted to the nonprotein compounds of pollen. However, individuals are rarely exposed to pure allergens, but rather to particles releasing the allergen, such as pollen grains or pollen-derived granules (107109). Notably, lipids are major components of pollen exine and exsudate (108). In addition, long chain unsaturated fatty acids in pollen, such as linolenic acid, serve as precursors for the biosynthesis of several plant hormones, such as dinor isoprostanes, recently termed phytoprostanes. These phytoprostanes are formed non-enzymatically via autooxidation in plants and structurally resemble prostaglandins and isoprostanes in humans (110112)."
"It has been demonstrated recently that pollen grain, under physiological exposure conditions, releases not only allergens but also bioactive lipids that activate human neutrophils and eosinophils in vitro (115117). Moreover, intact grains of pollen induce activation and maturation of dendritic cells in vitro, suggesting that pollen can act not only as allergen carrier but also as an adjuvant in the induction phase of the allergic immune response (118)."

# Pollen allergen carrying small particles
"In the early 1970s, Busse et al. (125) were the first to demonstrate the presence of specific ragweed allergens carried by small particles. By different techniques, this observation was confirmed and extended, first to ragweed-pollen allergen (126128). Subsequently, the same phenomenon was observed in grass-pollen allergen (129131), red oak-pollen allergen (132), Japanese cedar-pollen allergen (133), and birch-pollen allergen (134). With cascade impactors or other instruments that fractionate the sampled airborne matter into several size classes, it was established that these small particles range from some micrometers, i.e. 210 m (paucimicronic) to less than 1 m (submicronic) sizes (127, 128, 131, 133, 134)."