A Review of the Effects of Major Atmospheric Pollutants on Pollen Grains, Pollen Content, and Allergenicity

Abstract

This review summarizes the available data related to the effects of air pollution on pollen grains from different plant species. Several studies carried out either on in situ harvested pollen or on pollen exposed in different places more or less polluted are presented and discussed. The different experimental procedures used to monitor the impact of pollution on pollen grains and on various produced external or internal subparticles are listed. Physicochemical and biological effects of artificial pollution (gaseous and particulate) on pollen from different plants, in different laboratory conditions, are considered. The effects of polluted pollen grains, subparticles, and derived aeroallergens in animal models, in in vitro cell culture, on healthy human and allergic patients are described. Combined effects of atmospheric pollutants and pollen grains-derived biological material on allergic population are specifically discussed. Within the notion of "polluen," some methodological biases are underlined and research tracks in this field are proposed.

Figure 1

(a) Open-top chambers (OTCs) were located at Montardon site (10 km north of Pau, France). Technical characteristics of OTCs, close to those described by Heagle et al. [32, 33], have been already reported [34]. Each circular OTC had a diameter of 3 m and an open-top diameter of 2 m and was 2.8 m tall. It consisted of a galvanised iron frame covered with a polyethylene foil (Deltatex T2E). Ozone-free air (filtered air) or O₃-enriched air was blown all around the chamber above the canopy level. The flow rate was controlled to achieve an air exchange rate of 3.14 times per min at the canopy level. When supplied, extra ozone was generated by electrical discharge of pure oxygen and injected into the air stream. Extra ozone was equally released only from 10 a.m. to 5 p.m. (GMT) in order to simulate the normal period of ozone exposure. The control chamber received filtered air (before ambient air was blown in the chamber, it passed through a charcoal filter that removed almost totally ozone), while, in O₃-enriched OTC, O₃ concentration reached 100 μg/m³. Ozone was sequentially monitored in the three OTCs with an UV ozone analyser (Environnement SA, O₃ 41 M) under the control of a computer recording system. (b) Inside a filtered air chamber: in the foreground mature Dactylis glomerata plants with inflorescences can be seen. The air suction device of the OTC allowing measurement of the ozone concentration is noted with a red arrow.

Figure 2

Two-dimensional gel electrophoresis analysis of the water-soluble proteins from Dactylis glomerata pollen harvested in ventilated greenhouse with air (a, c, e) or with air containing ozone, 100 μg/m³, 8 hours per day (b, d, f). Pollen extract from Dactylis glomerata was submitted to an initial isoelectrofocusing separation followed by gel electrophoresis with SDS. The gels were either silver stained (a, b) or transferred on nitrocellulose incubated with 2 different grass pollen-sensitized patient sera (c–f). IgE binding was revealed using heavy chain specific antibody coupled to alkaline phosphatase (AP). The AP activity was detected using 5-bromo-4-chloro-3-indolyl phosphate and nitroblue tetrazolium (Sigma) in 0.1 M tris buffer pH 9.5. Isoelectric points (pI) values (at the bottom) and relative molecular mass (kDa, on the right) are indicated for each gel.

Figure 3

Experimental exposure of cypress and birch pollen with nitrogen dioxide (NO₂). (a) Cypress (25–30 μm) or birch (20 μm) pollen grains, filed on filter (0.22 μm), were aerosolized into a synthetic industrial air flow of 100 mL/min (allowing the flight of smaller particles than pollen) and sent into an impactor equipped solely with a PM₁₀ stage. Particle size distributions were measured, during 10 min, at the outlet of the impactor with an aerosol particle sizer (APS) (0.5–20 μm). (b) Pollen samples were moistened and then dried with air during 10 min (blue curves) and control samples were realized with industrial air (green curves). Impaction tests were also done with pollen grains artificially polluted with NO₂ (0.5% for 10 min) (red curves). Particle size distributions were normalized to show an equal number of pollen grains at 17 μm.