Dictionary of Allergies .. Air pollution and atopic sensitisation

Air pollution and atopic sensitisation

There have been several studies of the relationships between environmental factors, particularly air pollution, and attacks of rhinitis and asthma. This has been attributed to an increased exposure to air pollutants, which exert two effects. Firstly they have an adjuvant effect on sensitisation and IgE antibody production. Secondly they may cause airway inflammation both directly and by stimulation of irritant receptors and subsequent peptide release thus adding to and maintaining inflammation in the airway [1]). Until recently it was believed that the world-wide increase in the prevalence of asthma and other allergic diseases, especially of allergic rhinitis, particularly in industrial societies was due to air pollution. There is evidence that air pollution enhances not only the risk of allergy but may be also responsible for increasing prevalence rates of pollen allergies in highly polluted regions.

It has been shown that irritant gases, i.e. SO2,NO2 and O3, and airborn particulate matter (APM), especially diesel exhaust particulates, have both adjuvant activity for specific IgE production against common allergens in experimental animals and enhancing effects on allergic symptoms within sensitised individuals. Furthermore, pollen grains do not only carry allergens, but also incorporate pollutants when released into a polluted atmosphere. Pollen grains can accumulate heavy metals, i.e. lead, cadmium, and mercury, as well as sulfur, and the amount of sulfur per pollen dry weight seems to be a bioindicator for burden of the atmosphere with sulfuric aerosols. Behrendt et al (1992) studied the in situ interaction between pollen and airborn particulate matter (APM) as well as the effect of extracts of APM on grass pollen (Dactylis glomerata)[2].

The results indicate a direct in situ interaction between pollen surfaces and APM. This effect is prominent in industrialized regions with high emission of organic pollutants. It is also found to occur near roads with heavy traffic. There is morphological evidence for preactivation of pollen by organic extracts of APM. Aqueous extracts, however, directly induce the release of allergens with altered antigenicity. It was concluded that the generation and release of allergenic aerosols in a humidified air is initiated and mediated by substances adsorbed to APM. However opinions are divided; for example, in recent reviews, Barnes [3] concludes that there is little evidence that the increase in the prevalence of asthma is related to air pollution, while Rusznak et al [4] suggest that air pollutants may precipitate attacks of asthma and may have contributed to its increase. Epidimiological studies from different parts of the world have reported small but significant associations between asthma attacks and air pollutants, particularly ozone (O3) and particulates. Epidemiological studies have suggested possible interactions between aeroallergens and pollutants[5]. The ISAAC study (1998) indicates that air pollutants seem to have no causal connection with the increased occurrence of allergic diseases. For exam[le, the prevalence of allergic diseases is very high in New Zealand, where the air is very clan and clear. Allergic diseases are also more common in Western than Eastern Europe, although air pollution undoubtedly is much greater in the East than in the West[6].

ΡReferences

1. Zetterström, O.: The increased prevalence of allergic airway disease. Allergy, 1988:43(8):8-11.

2. Behrendt, h. et al: Interaction between Aeroallergens and Airborne Particulate Matter. Int Arch Allergy Immunol 1992;99:425-428

3. Barnes Pj: Air pollution and asthma. Postgrad Med J, 1994;70:319-25.

4. Rusznak C, et al: The impact of pollution on allergic disease. Allergy 1994;49 Suppl 18:21-7.

5. Rosas I, et al: Analysis of the relationships between environmental factors (aeroallergens, air pollution, and weather) and asthma emergency admissions to a hospital in Mexico city. Allergy 1998:53:393-401.

6. International Study of Asthma and Allergies in Childhood (ISAAC) Steering Committee. Worldwide variation in in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISAAC. Lancet 1998;351:1225-1232