Entomophilies (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. The pollen producing organs, stamens, consist of an anther attached to a filament. Allergenic pollens develop in and are released from pollen sacs contained in the anthers. Pollen sacs are lined with a nutritive cell layer, the tapetum. During its formation, each immature pollen grain secretes about itself a clear layer, the intine. Around this the tapetum deposits a multi layer exine composed of a polymer, sporopollenin. Release of pollen from the anther is known as anthesis. Drying creates gaps in the anther wall through which pollen escapes. Airborne pollen levels tend to increase during warm, dry, clears conditions and fall during cool, moist periods. 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 ragweed allergens have been associated with particles < 5 gm, and Amb a 1 (antigen E) activity has been found in submicronic particles. Pollen allergens can be extracted from the somatic portion of ragweed plants and may become airborne in vegetable debris. Furthermore, allergens might be eluted from pollen grains deposited ort moist surfaces, with dispersion of the resultant extract in droplets.
Air sampling relies on recovery of pollen grains for microscopic evaluation. As air sampled we are using volumetric devices like those which catches wind oriented spore, such as Lanzoni or Burkard traps, which are among the most versatile collectors for a variety of particles, including pollens. These devices also are especially useful for collecting fungal spores and other agents well below 10 ìm. Samplers should be placed on an unobstructed rooftop. Sampling closer to the ground sometimes reveals exposures not reflected by rooftop samplers. Personal collectors using small filters and compact pumps can determine individual exposure patterns. High volume samplers with fibreglass filters have been used to collect aerosols that can be extracted for immunochemical analysis. This sampling may provide a better overall view of total allergen exposure.
Most airborne pollens range in size from 12 to 70 mm. 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 and west coast areas, grasses may pollinate throughout much of the year. Anemophilous annuals (e.g., ragweed) generally shed pollen in midsummer to late summer, depending on their seed germination dates.
Establishing a dose response relationship between pollen exposure and symptoms is difficult. The range of severity for individuals is quite broad, and symp¬toms often reflect concurrent exposure to several al¬lergens. 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. Most de¬posit 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.
In the Urticaceae and Asteraceae families, nettle and pellitory show a lack of cross allergenicity. A 12,000 dalton allergen has been purified from pelli¬tory. 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 aller¬gens have been partially characterized. Some anti¬genic differences exist between giant and short rag¬weed species. In areas where Asteraceac other than ragweed are clinically significant, adequate immu¬notherapy will not be achieved by using ragweed ex¬tracts alone if pollen levels are significant.
The Chenopodiaceous and Amaranthaceae families contain major inducers of pollinosis in the western United States. An antigen from Russian thistle (Sal p 1) has been isolated. Members of the Chenopodiaceous are closely related and cross react strongly with the amaranth family. Russian thistle, however, appears to contain potent allergens (some of which are unique) that require special treatment. Russian thistle may provide relevant materials for some of the other chenopods, such as lamb's quarters, but generally chenopods of local significance require indi¬vidual therapy.
There are pollen productions over all months, however on spring the pollens concentration in the air in Europe, released from trees, weeds, and grasses, which rides on currents of air, enter human noses and throats, triggering a type of seasonal allergic rhinitis with several symptoms such as sneezing, eye and nasal itching, rhinorrea, etc. Of all the things that can cause an allergy, pollen is one of the most widespread. Many of the foods, drugs, or animals that cause allergies can be avoided to a great extent; even insects and household dust are escapable. Short of staying indoors when the pollen count is high and even that may not help, there is no easy way to evade windborne pollen.
Allergic Rhinitis is the most common of the allergic diseases and refers to seasonal nasal symptoms that are due to pollens.
Plants produce microscopic round or oval pollen grains to reproduce. In some species, the plant uses the pollen from its own flowers to fertilize itself. Other types must be cross-pollinated; that is, in order for fertilization to take place and seeds to form, pollen must be transferred from the flower of one plant to that of another plant of the same species. Insects do this job for certain flowering plants, while other plants rely on wind transport. Most allergenic pollen comes from plants that produce it in huge quantities.
Grasses and trees, too, are important sources of allergenic pollens. Although more than 1,000 species of grass grow in Europe, only a few produce highly allergenic pollen. These include timothy grass, poa, phleum pratense, bluegrass, grass, Bermuda grass, redtop grass, orchard grass, and sweet vernal grass. Trees that produce allergenic pollen include birch, olive, oak, ash, hickory, pecan, box elder, etc. Also in Southern European countries nettle and pellitory of the wall are produced in larges quantities and provoke sensitisation to a higher number of patients, who have allergic rhinitis or even asthma.
It is common to hear people say that they are allergic to colourful or scented flowers like roses. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to become sensitized to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of many flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees.
One of the most obvious features of pollen allergy is its seasonal predominance.
Symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollinating period that is more or less the same from year to year. Exactly when a plant starts to pollinate seems to depend on the relative length of night and day - and therefore on geographical location, rather than on the weather.
A pollen count, which is familiar to many people from local weather reports, is a measure of how much pollen is in the air. This count represents the concentration of all the pollen in the air in a certain area at a specific time. It is expressed in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods. Although a pollen count is an approximate and fluctuating measure, it is useful as a general guide for when it is advisable to stay indoors and avoid contact with the pollen. Please contact your national Aerobiology Network or an European network, such as the European Aeroallergen Network (E.A.N.).
Information to Patients
- There are several things that can be done against pollen allergies. The first and most effective is to avoid or minimize the contact with the allergen, such as pollen
- Avoid outdoor activities
- Avoid outdoor activities when the pollen count is high. Walks in the garden, mowing the lawn, camping or outdoor sports will increase exposure to pollens and the risk of allergy.
- Keep windows closed while driving. This will dramatically cut exposure to pollens. Cyclists should wear closed-visor helmets. Keep windows closed at home when the pollen count is high.
- Wearing dark classes whenever you are outside is an efficient and practical way to avoid eye problems.
- Take the medicine prescribed for you.
- Medication is the most efficient way to fight allergy symptoms. Make an appointment with a trained Clinical Immunologist for a correct diagnosis and the prescription of the most suitable medication.
- Prevention might be achieved via anti-allergy vaccines.
- No physical exercises outdoors during the pollen season
- Avoid alcohol beverages
- Wear sunglasses, which prevent to some extent your eyes from pollen contact and protect them.
- Schedule your holidays: to avoid contact with specific pollen you are allergic to, schedule your holidays in places with a low pollen count, for example snow or beach holidays. The Pollen Bulletin will tell you the high pollen season.
Last updated 07 November 2014