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Grass allergy increases the risk of tree pollen sensitization: A warning to urban planners☆☆☆★★★♢

1998; Elsevier BV; Volume: 102; Issue: 4 Linguagem: Inglês

10.1016/s0091-6749(98)70293-3

1097-6825

Frederico Costa Beber Vieira, Ellen Luciana da Silva Ferreira, Antonio M. Cruz,

Lichen and fungal ecology

Tree pollinosis is an important cause of allergy. Anemophilous tree pollens (blown in the wind) are the major cause of sensitization in predisposed individuals. Entomophilous tree pollens (too heavy to be airborne, carried by insects), are not usually considered a threat to the health. Such trees have been extensively planted along streets and squares.1Villaveces JW Tree allergy and the street-tree guide.J Asthma Res. 1973; 11: 47-56Crossref PubMed Scopus (4) Google Scholar Pollinosis has been reported in subtropical high altitude zones in Brazil.2Vieira FAM Negreiros EB Arborização Urbana como Influência na Epidemiologia da Polinose na Cidade de Caxias do Sul, RS, Brasil.Rev Soc Bras Alerg Imunol. 1989; 12: 114-119Google Scholar The predominant allergen in this region is grass pollen. The city of Caxias do Sul (29:10S, 51:10W; 800 m above sea level) has 302,000 inhabitants and belongs to the State of Rio Grande do Sul (Brazil), which borders Argentina and Uruguay. The mean temperature is 16.7°C, with 77% average humidity. The original forest coverture of 45% has been replaced by grasses both in the country side, used by cattle farmers, and also in the cities (Lolium multiflorum, Anthoxanthum odoratum, Holcus lanatus, Bromus inermis, Cynodon dactylon, and Paspalum notatum ). Ligustrum japonicum (lucidum) is a tree with primarily Entomophilous pollen from the Oleaceae family.3Lewis WH Vinay P North American pollinosis due to insect-pollinated plants.Ann Allergy. 1979; 42: 309-318PubMed Google Scholar In Caxias it accounts for 68% of 1680 trees counted in the downtown area. We found that 50.3% of 323 subjects in our clinic who had hay fever and were allergic to grass had a positive skin prick test response to Ligustrum pollen. These patients allergic to Ligustrum pollen and grass may have symptoms beyond grass pollen season when exposed to Ligustrum pollen. Nasal challenge with Ligustrum pollen extracts resulted in symptoms of rhinitis in 10 of 10 of these individuals. No association between Ligustrum sensitivity and other tree pollen was found when we tested for Acacia, Eucaliptus, and Platanus species.2Vieira FAM Negreiros EB Arborização Urbana como Influência na Epidemiologia da Polinose na Cidade de Caxias do Sul, RS, Brasil.Rev Soc Bras Alerg Imunol. 1989; 12: 114-119Google Scholar A priming effect on the nasal mucosa on repeated antigen exposure was demonstrated by Connell4Connel JT Quantitative intranasal pollen challenge. II. Effect of daily pollen challenge, environmental pollen exposure, and placebo challenge on the nasal membrane.J Allergy. 1968; 41: 123-139Abstract Full Text PDF PubMed Scopus (130) Google Scholar in 1968 by showing that repeated low-grade exposure of the respiratory mucosa to an allergen lowers the threshold of reactivity. Because Ligustrum pollinates in December through January right after the grass season, we thought grass allergy could be predisposing the respiratory mucosa to become sensitized to an uncommon aeroallergen. To further pursue this possibility, we conducted a cross-sectional study of a sample of the population of Caxias in the downtown area by using skin prick tests to aeroallergens and a standardized questionnaire. A total of 314 individuals (age range, 19 to 67 years; average, 37.8 years) agreed to participate. Our sample is comprised mostly of white European subjects. Allergen prick testing was performed with 11 common aeroallergens: Dermatophagoides pteronyssinus (1500 protein nitrogen units [PNU]/mL); D farinae (1500 PNU/mL); house dust (5000 PNU/mL); dander of sheep, cat, and dog (5000 PNU/mL); 2 pools of mixed molds (15,000 PNU/mL); and mixed grasses (10,000 PNU/mL) (Merck, Rio de Janeiro, Brazil). The tree pollen allergens were of Ligustrum species (10,000 PNU/mL) and Platanus acerifolia (10,000 PNU/mL) (Lester Laboratories, Buenos Aires, Argentina). The diameter of the wheal reaction was measured after 15 minutes by dividing the sum of the 2 largest perpendicular diameters by 2. All subjects were questioned to ensure they had not taken antihistamines. SPSS for Windows (SPSS Inc, Chicago, Ill) was used in performing multiple regression analysis. Subjects were gardeners, street sweepers, trash collectors, water system workers, and public electricians. Twelve of 314 (3.8%) had symptoms of seasonal rhinitis and asthma, 5.7% had perennial allergic rhinitis, and 1.9% had only asthma. One hundred ten (35%) of the 314 had at least 1 positive skin test response (wheal ≥3 mm). Grass test responses were positive in 31 (10%), and Ligustrum responses were positive in 15 (5%). Multiple regression analysis involving the variable skin reactivity to Ligustrum pollen (dependent) and each of all other allergen reactions shows a multiple correlation coefficient of 0.76 (F = 0.00001) for the variable grass, indicating that it accounts for 58% of variations on Ligustrum reaction. Such association was not found between Ligustrum pollen and any of the other allergens. Only 2 subjects were allergic to Ligustrum pollen without being sensitive to grass, whereas 13 of 31 individuals allergic to grass also had a cutaneous reaction to Ligustrum pollen. The relative prevalence of Ligustrum -positive test responses in grass-sensitive subjects is 59, which indicates that the chance of being allergic to Ligustrum is 59 times greater among grass-sensitive persons than in those with negative test responses to grass (Table I). Table IResults of skin prick tests to Ligustrum antigen according to the results of the grass skin testPositive Ligustrum responseNegative Lugustrum responseTotalPositive grass response131831Negative grass response2281283Total15299314 Open table in a new tab An association found in a cross-sectional study is no proof of causality. However, the strong correlation between grass and Ligustrum reactivity in the absence of association between this pollen and other aeroallergens supports our hypothesis of a predisposing effect of grass season exposure on subsequent Ligustrum exposure, resulting in greater sensitization. Nevertheless, it could have another, not exclusive, explanation. There could potentially be a cross-reactivity of IgE against some epitopes of grass and Ligustrum pollen. If this is true, it is very likely that the potential for priming and subsequent symptoms provoked by Ligustrum tree pollen is even greater. We therefore propose to further analyze whether a predisposing effect of a given pollen season may lead to sensitization to a subsequent different pollen natural exposure. If our findings are confirmed, planning the arborization of any town should take into account the risk of pollinosis in the region, even when using entomophilous pollen trees. We thank Professor Philip S. Norman and Alkis G. Togias, MD, from Johns Hopkins University, for their wise and kind advice; Professor Ronaldo Wasum (botanist) and Rubens Longhi (agronomist) from the Biological Science Center, University of Caxias do Sul, for their technical support; and Professor Jauner Oliveira from the Statistics and Mathematics Department who performed the statistical analysis of this work.