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Exposure of rye (Secale cereale) cultivars to elevated ozone levels increases the allergen content in pollen

2010; Elsevier BV; Volume: 126; Issue: 6 Linguagem: Inglês

10.1016/j.jaci.2010.06.012

1097-6825

Julia Eckl‐Dorna, Brigitte Klein, Thomas G. Reichenauer, Verena Niederberger, Rudolf Valenta,

Plant responses to elevated CO2

To the Editor: The increase of air pollution because of climate change and global warming represents a major challenge for humankind in this century. Changes in climate and air pollution have also been suggested to be potential factors behind the increasing prevalence of allergic diseases.1Beggs P.J. Impacts of climate change on aeroallergens: past and future.Clin Exp Allergy. 2004; 34: 1507-1513Crossref PubMed Scopus (327) Google Scholar In this context, it has been shown that particular matter (eg, diesel exhaust particles) can act as carriers and adjuvant for allergens, thereby enhancing the allergic immune response and promoting airway inflammation.2Parnia S. Brown J.L. Frew A.J. The role of pollutants in allergic sensitization and the development of asthma.Allergy. 2002; 57: 1111-1117Crossref PubMed Scopus (48) Google Scholar Furthermore, it has been demonstrated that rising concentrations of CO2 increase the production of ragweed pollen and their major allergen contents.3Rogers C.A. Wayne P.M. Macklin E.A. Mullenberg M.L. Wagner C.J. Epstein P.R. et al.Interaction of the onset of spring and elevated atmospheric CO2 on ragweed (Ambrosia artemisiifolia L.) pollen production.Environ Health Perspect. 2006; 114: 865-869Crossref PubMed Scopus (204) Google Scholar Environmental effects caused by the air pollutant ozone (O3) may occur at 2 levels. On the one hand, depletion of ozone in the stratosphere results in increased UV exposure. On the other hand, new low-level ozone is formed by the photochemical dissociation of nitrogen dioxide in the troposphere and has been reported to have adverse effects on human health. The latter ozone, which is a major component of photochemical smog, is particularly produced during the summer months in urban settings. Evidence has been provided that it may increase the content of a particular allergen (ie, group 5 allergen) in rye grass pollen.4Masuch G. Franz J.-T.H. Schoene K. Müsken H. Bergmann K.-C.H. Ozone increases group 5 allergen content of Lolium perenne.Allergy. 1997; 52: 874-875Crossref PubMed Scopus (38) Google Scholar However, a more recent study has suggested that grass pollen exposure to gaseous air pollutants (ie, O3, nitrogen dioxide, sulfur dioxide) decreases IgE recognition of major grass pollen allergens.5Rogerieux F. Godfrin D. Sénéchal H. Motta A.C. Marlière M. Peltre G. et al.Modifications of Phleum pratense grass pollen allergens following artificial exposure to gaseous air pollutants (O3, NO2, SO2).Int Arch Allergy Immunol. 2007; 143: 127-134Crossref PubMed Scopus (58) Google Scholar We designed a controlled experimental system to investigate the effects of increased tropospheric O3 levels on the contents of major allergens in pollen from a highly allergenic plant (ie, rye, Secale cereale). Two different rye cultivars, S cereale L cv “Motto” and S cereale L cv “Rapid,” were grown under controlled conditions in closed-top cabinets of a greenhouse. Two pots of each cultivar were grown in ambient air, and the other 2 were exposed to elevated O3 concentrations (80 ppb) during the day. This concentration corresponds to peak O3 levels measured during the month of May in Vienna, Austria (mean, 2006-2009). O3 was produced from pure oxygen with an O3 generator (Model 502; Fischer, Meckenheim/Bonn, Germany) and was distributed in the greenhouse by 3 fans to which perforated plastic tubes were connected. O3 exposure was carried out daily between 9 am and 5 pm for up to 107 days during plant growth. The O3 load of the air in the greenhouse was continuously monitored and was kept in a range of 79 ± 13 ppb (mean ± SD) in the O3 cabinet and 22 ± 12 ppb in the ambient air cabinet (control). Rye pollen was regarded as mature and thus ready to harvest immediately after the color of the anthers had turned from light yellow to dark yellow. Harvest of mature pollen was repeated at 2-day intervals, and pollen collected from 1 pot during this time was pooled at the end of the harvesting period. Pollen extracts were prepared by suspending exactly the same amounts of pollen (10 mg) in 1 mL sample buffer (62 mmol/L TRIS HCl [pH 6.8], 2.3% SDS, 10% glycerol, 0.1% bromophenol blue, 5% 2-mercaptoethanol) and by performing identical ultraturax treatment. Samples were then heated at 95°C for 20 minutes and centrifuged at 10,000g for 30 minutes. A total of 75 μL of the supernatant, corresponding to 75 μg extracted pollen, was loaded per lane of an SDS-protein gel and subjected to electrophoresis. Fig 1 shows that the protein content of the different preparations as visualized by silver staining was consistently higher for both rye cultivars when plants were grown in an environment with increased O3 levels. To study a potential association between protein and allergen contents in the pollen, we performed Western blot experiments by using antibody probes specific for group 1, group 5, and group 6 allergens and the panallergen profilin.6Valenta R. Duchene M. Pettenburger K. Sillaber C. Valent P. Bettelheim P. et al.Identification of profilin as a novel pollen allergen; IgE autoreactivity in sensitized individuals.Science. 1991; 253: 557-560Crossref PubMed Scopus (616) Google Scholar, 7Niederberger V. Laffer S. Fröschl R. Kraft D. Rumpold H. Kapiotis S. et al.IgE antibodies to recombinant pollen allergens (Phl p 1, Phl p 2, Phl p 5, and Bet v 2) account for a high percentage of grass pollen-specific IgE.J Allergy Clin Immunology. 1998; 101: 258-264Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar Nitrocellulose-blotted pollen extracts were incubated with rabbit antisera raised against recombinant allergens (Phl p 1, Phl p 5, Phl p 6, Bet v 2 [profiling]). Bound antibodies were detected by using 125I-labeled donkey-antirabbit antiserum and visualized by autoradiography. In the S cereale L cv “Motto,” exposure to higher O3 levels during the growth phase resulted in heightened content of each of the allergen groups tested (Fig 2, A and B). Mainly group 1 and profilin content were increased in the other rye cultivar (S cereale L cv “Rapid”). Our results thus clearly demonstrate that increased O3 levels during the growth phase of grasses result in a higher allergen content.Fig 2Immunoblot of pollen extracts from rye cultivated in ambient air or ozone-enriched environment. Two different S cereale L cultivars, “Motto” (S cereale M1 and M2) and “Rapid” (S cereale R1 and R2), were exposed to either ambient air (-) or 80ppm ozone (+). On harvest, proteins from pollen extracts were separated by SDS-PAGE and probed with antibodies specific for Phl p1, Phl p 5, Phl p 6, and profilin (A) or serum IgE from patients with allergy (patients 1 and 2; C) and quantified by densitometry (B and D). Extracts from equal amounts of pollen corresponding to 75 μg were loaded per lane. Molecular weights (kd) are displayed on the left.View Large Image Figure ViewerDownload Hi-res image Download (PPT) To investigate whether pollen from ozone-treated rye cultivars exhibits higher IgE reactivity and thus allergenic activity, nitrocellulose-blotted pollen extracts were probed with sera from 2 patients with grass pollen allergy. Fig 2, C and D, shows that IgE reactivity was stronger with the cultivar S cereale L cv “Motto” than with “Rapid,” but exposure to 80 ppb O3 during plant development resulted in increased reactivity of the sera from both patients with rye extract from O3-exposed plants. In conclusion, our experiments provide evidence that elevated O3 exposure during the growth phase of plants results in increased protein and allergen content of the pollen. This increase is demonstrated with IgG antibodies recognizing the protein backbone of the allergens and IgE antibodies from patients with allergy. The increase in allergen content on exposure to O3, a major component of photochemical smog that occurs particularly in urban regions during summer months, could be a mechanism linking the increase in air pollution with the rising prevalence of atopic diseases.