Allergenic Pollen in Europe and in the Mediterranean Area

Allergenic Pollen in Europe

and in the Mediterranean Area

Center of Allergy and Immunology of Algarve

R Jose Antonio Marques 3 C – 4

8500-700 Portimao

Portugal
e.mail: allergy@mail.telepac.pt
Clinical importance of Pollinosis is confined to flowered plants (namely the division of Spermatophyte) with, primarily, produced wind-dispersed pollens. Although such (anemophilous) form a floral minority everywhere, prodigious outputs of pollen continue to ensure their reproductive success.

Higher plants (as in tropical areas) exclusively use insects or bats, birds, etc. as self-directed vectors for pollen dispersal. Such species (entomophilous) produce relative few pollens grains but have evolved large, brightly, coloured blossoms and sweet nectars to attract conveyor organisms.

Some other plants with grouped and showy flowers in aggregate (amphiphilous) such acacias, goldenrods, sumac and wild grapes, whom have only a minority of grains windborne by insects? Only in large group have potency for air contamination?

Pollen prevalence at any site will reflect the strength and proximity of upwind sources and the activity of crosswinds both vertical and horizontal.

Pollens level are influenced strongly by the depth of the volume of air in which free mixing can occur, and this, in turn can reflect the prevailing profile of the lower atmosphere.

Overall, levels of airborne pollen are increased by warm, dry, clear conditions and fall during unseasonable, cold or wet periods.

Determinants of pollens output anemophilous species are not well understood but appear to include temperature, humidity, rainfall and light intensity. Anemophilous annuals, which must complete their life cycles in a single season, generally shed pollen in late spring to mid or late summer, depending on their seed germination dates.

When winter is harsh prevail blossom loss, which can be extensive, and flowering conditions can be unpredictable making tree pollination variable in date and intensity.

Others species with perennial rootstocks, such as grasses, nettles, hemp, plantains, etc., generally follow flowering from early spring to mid summer.

Despite several decades of active studies related to aerobiology, pollen prevalence data continue to offer:

• 
  Clues to potential offenders in new population centres
  
• 
  Evidence of extension exposure trends in communities even those with established database
  
• 
  Insight into a short period exposure burdens for clinical observations and investigative use
  

For practical reasons related to promote adequate information to patients suffering from pollinosis, we know that most pollen is released in the early morning hours with the rise in temperature and decline in relative humidity. With dispersal by wind currents, pollen levels usually peak in the afternoon or early evening. Wind can carry pollen for miles, resulting in high pollen counts far from the source. Pollens from trees and grasses are most problematic in spring and early summer, respectively; weed pollens predominate in midsummer.

Clinically important Pollinosis is primarily due to flowering plants with wind‑dispersed pollens. Although these anemophilous species form a minority of flowering plants, they produce prodigious amounts of pollen. Entomophilous (insect‑pollinated) plants produce relatively few pollen grains. Plants having only a portion of their pollen grains airborne are termed amphiphilous. Their role in Pollinosis is not clear.

Although pollen grains can travel several hundred miles, concentrations of windborne pollens generally decrease sharply within a few hundred meters of their source.

Intact pollen grains are presumed to be the primary carriers of allergen, but some allergens have been associated with particles of the pollens grain and their activity has been found in submicronic particles. Furthermore, allergens might be eluted from pollen grains deposited on humid surfaces, with dispersion of the resultant extract in droplets.

Most airborne pollens range in size from 12 to 70 m and certain features make identification.

Trees and other woody plants are the earliest to undergo pollination each growing season. Tree pollination especially varies in date and intensity. Non-woody perennial species (e.g., grasses) generally follow the trees from late spring to midsummer. In southern Europe grasses may pollinate from April to July.

Establishing a dose‑response relationship between pollen exposure and symptoms is difficult. The range of severity for individuals is quite broad, and symp­toms often reflect concurrent exposure to several al­lergens. Response usually increases with ongoing short‑term exposure (priming), and exposure involves aerosol fractions besides intact pollen grains. Pollens usually penetrate to the level of the glottis. As we have said above, most particles of grain pollens de­posit in the nose, pharynx, oesophagus, stomach, and eyes.

The protein molecules in pollens capable of sensitising patients generally range in size from 10,000 to 40,000 Daltons. Once the pollen grain is in contact with the upper airway mucous membranes, symptoms develop within a few minutes, suggesting that these proteins are rapidly eluted. Although individuals are exposed to many potentially allergenic pollens, only a relatively few pollens produce symptoms. This rel­ative restriction of sensitisation reflects the broad pat­terns of cross‑reactivity among proteins derived from different but taxonomically related plants.

Methods for assessing cross‑reactivity among pol­len extracts and their implication in individual symptoms are very interesting. In clinical practice this characteristic is essential to understand clinical symptoms after food ingestion in individuals sensitised to some pollens grains that have allergens commons to determinate grain pollen. The methodology may be divided into approaches that mea­sure all proteins or antigens (e.g., gel diffusion against animal antisera, isoelectric focusing, and crossed immunoelectrophoresis (CIEI) and those that examine the allergenic relationships of the extracts (e. g., RAST inhibition and crossed radioimmunoelectrophoresis (CRIEI). RAST inhibition cannot demonstrate to what extent individual allergens in two pollen extracts are related or unique. CRIE, although less quantitative than RAST, offers the advantage of separately analysing each allergen. These methods demonstrate con­siderable cross‑reactivity within and between many plant families.

For the Cupresssaceae, cedars, cypresses, and jun­ipers are important in pollinosis; other conifers have only minor allergenic significance. Marked cross reactivity occurs within the cypress family, with little cross‑reactivity extending to other conifers

The Fagaceae (beech) and Betulaccae (birch) fam­ilies produce pollens that strongly cross‑react. Birch species appear to be the most closely related to each other. Immunotherapy for one may be adequate to treat allergy to others and may also be sufficient to treat allergy to beech family members.

The Salicaccae (willows, poplars, and aspens) strongly cross‑react with each other and show some degree of cross‑reactivity with the birch and beech families, Oleaceae (olive, ash, and privet) show strong cross‑reactivity. Reports of cross‑reactivity in the Aceraccae (maple and box elder) are con­flicting.

Of the Poaceae, the subfamily Festucoideac con­tains most of the grasses important in causing allergic symptoms in the Europe. These grasses demonstrate extensive cross‑reactivity. For most al­lergic patients, treatment and testing may be con­ducted with one or a few members of this family. Purified Lolium (rye) allergens have been obtained, termed Lol p 1, 11, and 111 (formerly rye 1, 11, and 111). Eighty‑five to 95% of patients exhibit reactivity to the grass group 1 allergens (Lol p 1 and its homologs). A subfamily, Eragostoideae, contains one predominant allergenic member, Bermuda grass. Separate testing and treatment is necessary for Bermuda, Bahia, and Johnson grasses because of their low degree of cross reactivity with the Festucoideae.

In the Urticaceae and Asteraceae families, nettle and pellitory show a lack of cross‑allergenicity. A 12,000 dalton allergen has been purified from pelli­tory. Among the composites, major allergens have been identified from the tribe Ambrosicae. The most important is Ambrosia artemisia (short ragweed) allergen Amb a 1 (antigen E). Other purified antigens include Amb a 11 (antigen K), Amb a 111 (Ra3), Amb a V (Ra5), and Amb a VI (Ra6). Several other aller­gens have been partially characterized. Some anti­genic differences exist between giant and short rag­weed species. In areas where Asteraceac other than ragweed are clinically significant, adequate immu­notherapy will not be achieved by using ragweed ex­tracts alone if pollen levels are significant.

The Chenopodiaceous and Amaranthaceae families contain major inducers of pollinosis in the central Europe. Members of the Chenopodiaceous are closely related and cross‑react strongly with the amaranth family.

The data should be related to continuous volumetric data collected with a Burkard or Lanzoni pollen trap, over periods from 3 to 5 years.

The calendars should integrate a data selection of the 15 taxa considered comprised ten prescribed taxa selected on the basis of either their abundant airborne occurrence and/or their allergenic significance; and five additional taxa selected from ten allergenically less important, or aerobiologically less frequent taxa.

In 1999 an European pollens calendar was made and published with the name of “The European Pollen Calendar” by EAACI with the participation of European Federation of Asthma and allergy associations (EFA) an UCB Institute.

January

Hazel flowers between December and April. The symptoms of pollinosis, which start in January/February and last up to two mouths, can occur far from hazel trees. As a consequence of its early pollination and its allergenic cross-reactivity with birch, hazel can induce the start of sensitization to birch. Cypress flowers from February until April.

February

Alder flowers between February and April. Alder-pollen allergens cross-react with birch and hazel. Parietaria flowers from January to November. It is found throughout Europe but prevalently in Mediterranean areas. Asthma associated with rhinoconjunctivitis is the main symptom of Parietaria pollinosis.

Although not highly allergenic, mimosa has been known to cause proximity pollinosis; its best to avoid smelling these flowers.

March

Grasses start to pollinate along the Mediterranean coasts. Hazel and alder are in flower in central and northern Europe. Birch starts to flower along the coasts of the Black Sea.

Adhere to your treatment plan and enjoy spring.

April

Birch flowers in central Europe, and the hay fever season with clinical symptoms caused by Parietaria pollen begins in southern areas. Parietaria is a major cause of seasonal asthma: symptoms can start to appear at a threshold concentration of about 30 pollen granules/m³.

Entomophilous plants (plants pollinated by insects, e.g., roses and orchids) tend to be very colorful so as to attract insects. They are less allergenic and produce much less pollen than anemophilous plants; their pollen is heavier and less likely to be released into the air.

May

The concentration of grass pollen reaches its peak in Mediterranean areas. Olive trees start to flower around the Mediterranean, and birch starts to flower in central and northern Europe. Symptoms of olive allergy can occur after a brief exposure, and subjects allergic to other pollens are at a grater risk. Olive pollen can cause conjunctivitis and in a high percent of cases, cough and/or asthma.

June

This is the peak season for grass pollination in northern Europe. The concentrations of olive and Parietaria pollen are still high in southern Europe.

July

Mugwort pollination starts in mid-July and ends in mid-October. Allergy is usually associated with sensitization to other pollens, so symptoms can last beyond the flowering period. Mugwort pollen is relatively heavy and not easily dispersed into the air, but large quantities are produced. In July concentrations of grass pollen are still high in northern Europe. Parietaria continues to be present in southern areas, and starts to appear in southern parts of the British Isles.

August

Pollen concentrations are low in Mediterranean areas. High concentrations of mugwort pollen are found in central and northern Europe. The ragweed pollen season starts in central Europe. Grasses are also flowering in the archipelagoes off the east coast of Sweden.

September

There is a low pollination month in central and northern Europe. Ragweed pollination continues in central Europe. In Mediterranean areas, mugwort pollen makes its appearance; there is a second wave of Parietaria flowering (less intense than the spring flowering), and the Chenopodiaceae are in flower.

Rain-washes pollen out of the air, but it can be followed by a burst of blooming and pollination. There is more pollen in the air on windy days.

October

Parietaria and mugwort are still flowering around the Mediterranean. There are pockets of ragweed and mugwort pollination in central Europe.

Parietaria still flowers around Mediterranean coastal waters.

November

The long pollination season in the Mediterranean areas is drawing to a close, and the pollination cycle resumes with the onset of cypress flowering.

December

Atmospheric pollen concentrations are very low at this time of the year.
RECOMMENDED FURTHER READING
D’Amato G.,Spieksma F.Th.M.Bonini S. - Allergenic pollen and pollinosis in Europe. Blackwell Science, Oxford, UK, 1991

D’Amato G.,Spieksma F.Th.M.,Liccardi G. et al - Pollen-related allergy in Europe. Position Paper of the European Academy of Allergology and Clinical Immunology. Allergy 1998; 53:567-78.

Respiratory allergy. European Federation of Asthma and Allergy Associations. 2000

European Allergy White Paper. The UCB Institute of Allergy. Belgium, 1997

Muilenberg M, Burge Harriet – Aerobiology. Lewis Publishers. USA. 1996

Mc Michael A.J., Haines A., Sloff R and Kovats S. –Climate Change and Human Health. WHO/EHG/96.7 - WHO, WMO and UNEP, Geneva, Switzerland, 1996

Mandrioli P., Comtois P, Levizzani V. – Methods in Aerobiology. Pitagora Editrice. Bologna. Italy. 1998.

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