Birch Pollen Research Articles

Molecular allergy diagnosis is sensitive and avoids misdiagnosis in patients sensitized to seasonal allergens.

The specificity of extract-based pollen allergy diagnosis is decreased due to cross-reactivity via cross-reactive carbohydrate determinants (CCDs) or panallergens such as profilins or polcalcins. This study aimed to explore the prevalence of sensitization to seasonal extracts, CCDs, profilin and polcalcin and investigate the sensitivity and specificity of seasonal molecular allergy diagnosis (MAD) using commercially available test methods. 2948 patients were screened for specific immunoglobulin E to ash, birch, mugwort, ragweed and timothy grass pollen extracts and grouped according to the number of positive tests (1-5). 100 patients from each group and a control group were randomly selected to calculate the prevalence of CCD and panallergen sensitization. With 742 patients, sensitivity and specificity of MAD (Alt a 1, Fra/Ole e 1, Bet v 1, Phl p 1, Art v 1, and Amb a 1) was determined. 1627 patients (55.2%) were positive to at least one, and 1002 patients (34.0%) were positive to multiple of the five pollen allergens investigated; 18.5% of the pollen-sensitized patients had sensitization to CCDs or panallergens. Specifically, sensitization to CCDs, profilins, and polcalcins was observed in 8.7%, 10.9%, and 2.9% of these patients, respectively. The sensitivity of MAD was high, with sensitivities between 96.2% and 100% using ImmunoCAP and 91.5% and 100% using ALEX2 . Specificity was 100% for both assays. Due to cross-reactivity, about one-fifth of pollen-sensitized patients is at risk of misdiagnosis. However, MAD is sensitive, specific and helps to avoid misdiagnosis and select primary allergen sources for immunotherapy.

Relationship between IgE Levels Specific for Ragweed Pollen Extract, Amb a 1 and Cross-Reactive Allergen Molecules

Ragweed (Ambrosia artemisiifolia) pollen is a major endemic allergen source responsible for severe allergic manifestations in IgE-sensitized allergic patients. It contains the major allergen Amb a 1 and cross-reactive allergen molecules, such as the cytoskeletal protein profilin, Amb a 8 and calcium-binding allergens Amb a 9 and Amb a 10. To assess the importance of Amb a 1, profilin and calcium-binding allergen, the IgE reactivity profiles of clinically well-characterized 150 ragweed pollen-allergic patients were analysed regarding specific IgE levels for Amb a 1 and cross-reactive allergen molecules by quantitative ImmunoCAP measurements, IgE ELISA and by basophil activation experiments. By quantifying allergen-specific IgE levels we found that Amb a 1-specific IgE levels accounted for more than 50% of ragweed pollen-specific IgE in the majority of ragweed pollen-allergic patients. However, approximately 20% of patients were sensitized to profilin and the calcium-binding allergens, Amb a 9 and Amb a 10, respectively. As shown by IgE inhibition experiments, Amb a 8 showed extensive cross-reactivity with profilins from birch (Bet v 2), timothy grass (Phl p 12) and mugwort pollen (Art v 4) and was identified as a highly allergenic molecule by basophil activation testing. Our study indicates that molecular diagnosis performed by the quantification of specific IgE to Amb a 1, Amb a 8, Amb a 9 and Amb a 10 is useful to diagnose genuine sensitization to ragweed pollen and to identify patients who are sensitized to highly cross-reactive allergen molecules present in pollen from unrelated plants, in order to enable precision medicine-based approaches for the treatment and prevention of pollen allergy in areas with complex pollen sensitization.

Chemical modification by peroxynitrite enhances TLR4 activation of the grass pollen allergen Phl p 5.

The chemical modification of aeroallergens by reactive oxygen and nitrogen species (ROS/RNS) may contribute to the growing prevalence of respiratory allergies in industrialized countries. Post-translational modifications can alter the immunological properties of proteins, but the underlying mechanisms and effects are not well understood. In this study, we investigate the Toll-like receptor 4 (TLR4) activation of the major birch and grass pollen allergens Bet v 1 and Phl p 5, and how the physiological oxidant peroxynitrite (ONOO-) changes the TLR4 activation through protein nitration and the formation of protein dimers and higher oligomers. Of the two allergens, Bet v 1 exhibited no TLR4 activation, but we found TLR4 activation of Phl p 5, which increased after modification with ONOO- and may play a role in the sensitization against this grass pollen allergen. We attribute the TLR4 activation mainly to the two-domain structure of Phl p 5 which may promote TLR4 dimerization and activation. The enhanced TLR4 signaling of the modified allergen indicates that the ONOO--induced modifications affect relevant protein-receptor interactions. This may lead to increased sensitization to the grass pollen allergen and thus contribute to the increasing prevalence of allergies in the Anthropocene, the present era of globally pervasive anthropogenic influence on the environment.

Attributing long-term changes in airborne birch and grass pollen concentrations to climate change and vegetation dynamics

Changes in climate and land-use may elicit an increased emission of allergenic pollen amounts in the air, causing a rise in respiratory allergies and affecting public health more than previously thought. Here we have used a well-established pollen transport model SILAM (System for Integrated modeLling of Atmospheric coMposition) for attributing the long-term changes in airborne pollen concentrations of birches and grasses to climate change and vegetation dynamics. The pollen transport model is applied for Belgium and is driven by ECMWF ERA5 meteorological data (European Centre for Medium-Range Weather Forecasts, fifth generation of ECMWF atmospheric reanalysis of the global climate). The dynamic vegetation components of the model are based on multi-decadal datasets for 1982–2019 on spatially distributed birch and grass pollen emission sources. For each model gridcell we have computed the change rate of the seasonal birch and grass pollen cycles based on daily pollen concentrations, and of the daily meteorological model input. Finally, the gridcell based association between trends in pollen and climate change are derived. Our findings show that during the period 1982–2019 a strong increase in birch pollen concentrations is associated with increasing radiation, decreasing precipitation and decreasing horizontal wind speed near the surface. A strong decrease of grass pollen concentrations over time is driven by a decreasing trend in grass pollen sources, and it is also associated with decreasing precipitation. The magnitude of the associations between meteorology and airborne birch pollen concentrations are almost twice the association between meteorology and grass pollen, and the spatial variations are substantial even on the scales of small countries. The specific contribution of birch tree and pollen production dynamics to the concentrations of birch pollen in the air over time is highly associated with wind speed and precipitation. Introducing the inter-seasonal variation in birch pollen production during the period 1982–2019 intensifies the climate induced increase of airborne birch pollen concentrations with ∼6%. In contrast, the grass pollen production dynamics resulted into ∼10 times less grass pollen over the studied period compared to climate change effects.

Prevalence of common sensitizing aeroallergens in patients with atopic dermatitis.

Atopic dermatitis (AD), a skin disease burden worldwide, is a complex, multifactorial, chronic inflammatory disease. Prevalence of AD is increasing in developing countries and identifying the causative allergens is a major challenge. Aeroallergens are shown to aggravate atopic dermatitis. Explore the prevalence of aeroallergens sensitization in patients with AD and its possible relation with AD severity. Cross-sectional study of 132 patients diagnosed to have atopic dermatitis. Atopy was detected by serum specific IgE to a panel of the most encountered aeroallergens. From the 132 patients, elevated specific IgE was detected in 72.7% from which 59.1% were mild and 86.4% are moderate/severe as well as 15.9% are mono-sensitized and 54.5% are poly-sensitized with poly-sensitization being more in severe cases compared to mild cases (68.2% vs 4.5%). Regarding specific IgE to different aeroallergens, the most prevalent were Dermatophagoides pteronyssinus (50%), followed by Dermatophagoides farinae (34.1%), Birch pollen (20.5%), cat epithelium (18.2%) Regweed (15.9%), and Cockroach (9.1%). However, moderate to severe cases were more sensitized to candida (p=0.012), mix grass pollen (p=0.002), ragweed (0.00), mite (p=0.037) and cat epithelium (p=0.007). Dermatophagoides pteronyssinus, Dermatophagoides farinae, Birch pollen, cat epithelium Regweed and Cockroach are the most frequent sensitizing aeroallergens in atopic dermatitis.

Subcutaneous immunotherapy with mannan-conjugated birch pollen allergens shows long-term effects already after 2 years of treatment by inducing a significant immune response in birch pollen allergic patients

Allergen immunotherapies aim to change the immune system in order to alleviate allergy symptoms in the long term. These therapies usually last several years, but first effects can already be detected after 1-2 years. Here, we determine the immunologic effects of 10.000 mTU/mL mannan-conjugated birch pollen allergen (T502).

Mannan-conjugated birch pollen allergoids reduce the combined symptom and medication score in birch pollen allergic patients already in the first treatment year and further decreases with prolonged treatment duration

The success of allergen immunotherapy for the treatment of allergic rhinoconjunctivitis is most evident during the respective pollen season. Here, we evaluated the combined symptom and medication score (CSMS) from 3 studies in patients with allergic rhinoconjunctivitis treated with mannan-conjugated birch pollen allergoids (T502).

Clinical Development of Mannan conjugated birch pollen allergoids for the treatment of birch pollen allergic patients – from first-in-human to approval in 3 studies

The aim of a drug development program for allergen immunotherapies is to get market authorization based on a good efficacy and safety/tolerability profile. Here, we describe the clinical development of Mannan conjugated birch pollen allergoids (T502) for the treatment of allergic rhinitis/rhinoconjunctivitis.

Asthma responses in birch allergic rhinitis (AR) with and without known birch-related asthma

Birch pollen mainly induces allergic rhinoconjunctivitis. A considerable discordance between patient reported asthma symptoms and objective asthma responses was observed during birch allergen challenges in ALYATEC Environmental Exposure Chamber (EEC).

Subcutaneous immunotherapy with mannan-conjugated birch pollen allergoids is safe and well tolerated – data from 3 sequential trials

Subcutaneous immunotherapy has not only to be effective, but also needs to be safe and well tolerated in order to be accepted by physicians and patients. Here we show the safety data from 2 double-blind, placebo-controlled studies and 1 open follow-up study with mannan-conjugated birch pollen allergoids (T502).

A Cost-Utility Analysis of SQ® Tree SLIT-Tablet versus Placebo in the Treatment of Birch Pollen Allergic Rhinitis from a Swedish Societal Perspective.

Allergic rhinitis (AR) is an immunoglobulin E antibody-mediated inflammatory condition that arises in response to inhaled allergens such as pollen. Pollens from trees in the birch homologous group are the most common allergenic tree pollens in Northern and Central Europe and North America. SQ® Tree SLIT-Tablet (ITULAZAX®) is a sublingual immunotherapy tablet indicated for moderate-to-severe AR and/or conjunctivitis induced by pollen from the birch homologous group. The present analysis evaluated the cost-utility of treating adults with AR with SQ Tree SLIT-Tablet versus placebo, both in combination with symptom-relieving medications, from a Swedish societal perspective. A model was developed to evaluate changes in cost and quality of life associated with using SQ Tree SLIT-Tablet relative to placebo in an adult population of individuals with AR. The model captured costs associated with symptom-relieving medications, healthcare professional interactions, SQ Tree SLIT-Tablet, and indirect costs arising from absenteeism and reduced workplace productivity. The analysis was conducted over 10 years with costs captured in 2021 Swedish Krona (SEK) and future costs and effects discounted at 3% per annum. One-way and probabilistic sensitivity analyses were conducted. Treatment with SQ Tree SLIT-Tablet resulted in an improvement of 0.041 quality-adjusted life years (QALYs) over 10 years versus placebo. From a Swedish societal perspective, costs increased by SEK 9077 over the same period, resulting in an incremental cost-utility ratio of SEK 223,445 per QALY gained. One-way sensitivity analysis showed that the model was most sensitive to assumptions around the disease-modifying effect of SQ Tree SLIT-Tablet. SQ Tree SLIT-Tablet improved quality of life in moderate-to-severe AR and/or conjunctivitis induced by pollen from the birch homologous group in Sweden, with only a modest increase in societal costs over a medium-term time horizon, representing good value for money at a willingness-to-pay threshold of SEK 700,000 per QALY.

Characterization and Quantification of Mal d 1 Isoallergen Profiles and Contents in Traditional and Commercial Apple Varieties by Mass Spectrometry

The apple allergy in Northern Europe is a cross-reaction to the birch pollen allergy. No correlation between the allergenicity of an apple variety and the content of the major apple allergen Mal d 1, a homologue to the Bet v 1 allergen in birch, could be found using ELISA, so far. Therefore, an impact of polyphenols and/or differences in the isoallergen profile are discussed. To allow a more detailed analysis of the Mal d 1 content and the isoallergen profile, a mass spectrometric method was applied to investigate differences in the flesh and peel of 10 traditional varieties and 10 commercial breeds. The data revealed often, but not always, lower Mal d 1 contents in traditional varieties grown in orchard meadows, which was more obvious in the flesh. Differences among the peels were less pronounced. A closer look at the individual isoallergens 1.01, 1.02, 1.03, and 1.06 reveals an increased impact of the minor isoallergens 1.03 and 1.06 on the allergenic potential, since commercial breeds like Braeburn, Santana, and Holstein Cox, which are considered to have reduced allergenic potentials, were characterized by low levels of these isoallergens.

Air pollution in the places of Betula pendula growth and development changes the physicochemical properties and the main allergen content of its pollen.

Pollen allergy becomes an increasing problem for humans, especially in the regions, where the air pollution level increases due to the traffic and urbanization. These factors may also affect the physiological activity of plants, causing changes in pollen allergenicity. The aim of the study was to estimate the influence of air pollutants on the chemical composition of birch pollen and the secondary structures of the Bet v1 protein. The research was conducted in seven locations in Malopolska region, South of Poland of a different pollution level. We have found slight fluctuations in the values of parameters describing the photosynthetic light reactions, similar spectra of leaf reflectance and the negligible differences in the discrimination values of the δ13C carbon isotope were found. The obtained results show a minor effect of a degree of pollution on the physiological condition B. pendula specimen. On the other hand, mean Bet v1 concentration measured in pollen samples collected in Kraków was significantly higher than in less polluted places (p = .03886), while FT-Raman spectra showed the most distinct variations in the wavenumbers characteristic of proteins. Pollen collected at sites of the increased NOx and PM concentration, show the highest percentage values of potential aggregated forms and antiparallel β-sheets in the expense of α-helix, presenting a substantial impact on chemical compounds of pollen, Bet v1 concentration and on formation of the secondary structure of proteins, what can influence their functions.

Mas-related G protein-coupled receptor MRGPRX2 in human basophils: Expression and functional studies.

Occupancy of MRGPRX2 heralds a new era in our understandings of immediate drug hypersensitivity reactions (IDHRs), but a constitutive expression of this receptor by basophils is debated. To explore the expression and functionality of MRGPRX2 in and on basophils. Basophils from patients with birch pollen allergy, IDHRs to moxifloxacin, and healthy controls were studied in different conditions, that is, in rest, after stimulation with anti-IgE, recombinant major birch pollen allergen (rBet v 1), moxifloxacin, fMLP, substance P (SP), or other potential basophil secretagogues. In a separate set of experiments, basophils were studied after purification and resuspension in different media. Resting whole blood basophils barely express MRGPRX2 on their surface and are unresponsive to SP or moxifloxacin. However, surface MRGPRX2 is quickly upregulated upon incubation with anti-IgE or fMLP. Pre-stimulation with anti-IgE can induce a synergic effect on basophil degranulation in IgE-responsive subjects after incubation with SP or moxifloxacin, provided that basophils have been obtained from patients who experienced an IDHR to moxifloxacin. Cell purification can trigger a "spontaneous" and functional upregulation of MRGPRX2 on basophils, not seen in whole blood cells, and its surface density can be influenced by distinct culture media. Basophils barely express MRGPRX2 in resting conditions. However, the receptor can be quickly upregulated after stimulation with anti-IgE, fMLP, or after purification, making cells responsive to MRGPRX2 occupation. We anticipate that such "conditioned" basophils constitute a model to explore MRGPRX2 agonism or antagonism, including IDHRs originating from the occupation of this receptor.

The role of IgG1 and IgG4 as dominant IgE-blocking antibodies shifts during allergen immunotherapy

The induction of allergen-specific IgE-blocking antibodies is a hallmark of allergen immunotherapy (AIT). The inhibitory bioactivity has largely been attributed to IgG4; however, our recent studies indicated the dominance of IgG1 early in AIT. Here, the IgE-blocking activity and avidity of allergen-specific IgG1 and IgG4 antibodies were monitored throughout 3 years of treatment. Serum samples from 24 patients were collected before and regularly during AIT with birch pollen. Bet v 1-specific IgG1 and IgG4 levels were determined by ELISA and ImmunoCAP, respectively. Unmodified and IgG1- or IgG4-depleted samples were compared for their inhibition of Bet v 1-induced basophil activation. The stability of Bet v 1-antibody complexes was compared by ELISA and by surface plasmon resonance. Bet v 1-specific IgG1 and IgG4 levels peaked at 12 and 24 months of AIT, respectively. Serological IgE-blocking peaked at 6 months and remained high thereafter. In the first year of therapy, depletion of IgG1 clearly diminished the inhibition of basophil activation while the absence of IgG4 hardly reduced IgE-blocking. Then, IgG4 became the main inhibitory isotype in most individuals. Both isotypes displayed high avidity to Bet v 1 ab initio of AIT, which did not increase during treatment. Bet v 1-IgG1 complexes were enduringly more stable than Bet v 1-IgG4 complexes were. In spite of the constant avidity of AIT-induced allergen-specific IgG1 and IgG4 antibodies, their dominance in IgE-blocking shifted in the course of treatment. The blocking activity of allergen-specific IgG1 should not be underestimated, particularly early in AIT.

Cationic liposomes bearing Bet v 1 by coiled coil-formation are hypo-allergenic and induce strong immunogenicity in mice.

Although aluminum hydroxide (alum) is widely accepted and used as safe vaccine adjuvant, there is some concern about possible toxicity upon long-lasting repeated exposure during subcutaneous allergen immunotherapy (SCIT). Our objective was to evaluate allergen-bearing liposomes as possible alternative for alum-adsorption in SCIT. A self-assembling, coiled-coil forming peptide pair was used to anchor the major birch pollen allergen Bet v 1 to the surface of cationic liposomes. The resulting nanoparticulate liposomes were characterized with respect to their physicochemical, allergenic and immunological properties. Allergenicity was studied by ImmunoCAP inhibition and rat basophil leukemia (RBL) cell assays. Immunogenicity (immunoglobulin responses) and immune skewing (cytokine responses) were evaluated upon immunization of naïve mice, and compared to alum-adsorbed Bet v 1. Bet v 1-bearing cationic liposomes with a diameter of ∼200 nm showed a positive zeta potential. The coiled-coil conjugation of Bet v 1 to the surface of liposomes resulted in about a 15-fold lower allergenicity than soluble Bet v 1 as judged by RBL assays. Moreover, the nanoparticles induced Bet v 1-specific IgG1/IgG2a responses in mice that were several orders of magnitude higher than those induced by alum-adsorbed Bet v 1. This strong humoral response was accompanied by a relatively strong IL-10 induction upon PBMC stimulation with Bet v 1. In conclusion, their hypo-allergenic properties, combined with their capacity to induce a strong humoral immune response and a relatively strong IL-10 production, makes these allergen-covered cationic liposomes a promising alternative for aluminum salt-adsorption of allergen currently used in SCIT.

Sadchikov Pavel E. Features of Molecular Sensitisation Profile in Infants with Risk of Allergic Diseases

Background. For now, there is little data on sensitivity features to specific allergen antigens in infants with initial allergy manifestations.Objective. The aim of the study is to determine the features of the primary molecular sensitisation profile in infants with risk of atopic disease according to their postnatal age.Methods. Full-term infants with burdened familial allergic history and/or skin/gastrointestinal allergy symptoms were examined: Group 1 — 50 children, age — 2.0 [1.0–3.0] months; Group 2 — 35 children, age — 9.0 [8.0–11.0] months.Results. The hereditary atopy risk was observed in 74% of cases (37/50) in Group 1 and in 71% of cases (25/35) in Group 2. 38% of children (19/50) in Group 1 were breastfed, in Group 2 — 60% of children (21/35). Supplemental feeding was implemented in 5.5 [5.0–6.0] months. Sensitisation was reported in 10% and 37% of children. Children of Group 1 were sensitised to food allergen antigens: cow's milk/meat (Bos d 6, Bos d 8), egg-white (Gal d 1, Gal d 2, Gal d 3), soybeans (Gly m 6), shrimps (Pen m 4); airborne allergens: house dust mite (Blo t 5, Der h 10), Anisakidae (Ani s 3), cockroach (Bla g 7). Children of Group 2 were sensitised to food allergen antigens: cow's milk (Bos d 6), egg-white (Gal d 1, Gal d 2), soybeans (Gly m 6), peanut (Ara h 1, Ara h 2, Ara h 6), kiwi (Act d 1), corn (Tri a 19); airborne allergens: cat (Fel d 1, Fel d 4), birch pollen (Bet v 1). Polyvalent sensitisation was revealed in 4% and 6% of cases, respectively.Conclusion. Infants have much wider range of allergens to which they are sensitive than it is commonly believed. Beside obligate food allergens, sensitisation can be caused by airborne allergens: house dust mites, epidermal, birch pollen; crossreactive component — tropomyosin.

Mechanistic insights into silica nanoparticle-allergen interactions on antigen presenting cell function in the context of allergic reactions.

The incorporation of nanomaterials into consumer products has substantially increased in recent years, raising concerns about their safety. The inherent physicochemical properties of nanoparticles allow them to cross epithelial barriers and gain access to immunocompetent cells. Nanoparticles in cosmetic products can potentially interact with environmental allergens, forming a protein corona, and together penetrate through damaged skin. Allergen-nanoparticle interactions may influence the immune response, eventually resulting in an adverse or beneficial outcome in terms of allergic reactivity. This study determines the impact of silica nanoparticle-allergen interactions on allergic sensitization by studying the major molecular mechanisms affecting allergic responses. The major birch pollen allergen Bet v 1 was chosen as a model allergen and the birch pollen extract as a comparator. Key events in immunotoxicity including allergen uptake, processing, presentation, expression of costimulatory molecules and cytokine release were studied in human monocyte-derived dendritic cells. Using an in vivo sensitization model, murine Bet v 1-specific IgG and IgE levels were monitored. Upon the interaction of allergens with silica nanoparticles, we observed an enhanced uptake of the allergen by macropinocytosis, improved proteolytic processing, and presentation concomitant with a propensity to increase allergen-specific IgG2a and decrease IgE antibody levels. Together, these events suggest that upon nanoparticle interactions the immune response is biased towards a type 1 inflammatory profile, characterized by the upregulation of T helper 1 (Th1) cells. In conclusion, the interaction of the birch pollen allergen with silica nanoparticles will not worsen allergic sensitization, a state of type 2-inflammation, but rather seems to decrease it by skewing towards a Th1-dominated immune response.

Особенности формирования субфоссильных спорово-пыльцевых спектров острова Кетой (Центральные Курилы)

The composition and ratios of main components of pollen assemblages from the surface layer of peatlands, soils, lake sediments, and alluvial silts in different parts of the Ketoi Island were analyzed. The island, despite its small size, is distinguished by a complex organization of the landscapes. The pollen spectra represent well the local vegetation at the sampling sites, regardless of the genesis of sediments. Pollen brought from adjacent territories does not have a significant effect on the composition of pollen spectra. The spectra from soil deposits in the southeastern part of the island are represented by heather pollen; in the southwestern part, by tree pollen, mostly Siberian dwarf pine, alder, and birch pollen. Among nonarborescent pollen, Asteraceae and Ericaceae are dominant. The pollen spectra obtained from pioneer soil in the western part of the island consist of club moss spores (Lycopodium clavatum), which represent communities on overgrown rockfall deposits. The assemblages of the surface layer of peatlands contain large amounts of sedge and grass pollen. The pollen spectra from alluvial silts represent the vegetation of small valleys, where alder, dwarf pine, and Erman’s birch along the sides are common. The pollen spectra from the sediments of small lakes represent local biotic communities very well. Allochthonous pollen of dark coniferous and broad-leaved trees is present in the spectra in small quantities, except for two samples. This pollen was brought from the southern islands, including those of Japan. The data obtained can be used for paleogeographic reconstructions in the analysis of the formation of pollen spectra on small oceanic islands.

Exercise-induced bronchoconstriction is associated with air humidity and particulate matter concentration in preschool children.

Long-term exposure to air pollution is connected to asthma morbidity in children. Exercise-induced bronchoconstriction (EIB) is common in asthma, and the free running test outdoors is an important method for diagnosing asthma in children. It is not known whether momentary air pollution exposure affects the results of outdoor exercise tests in children. We analyzed all reliable exercise challenge tests with impulse oscillometry in children (n = 868) performed between January 2012 and April 2015 at Tampere University Hospital. Pollutant concentrations (PM2.5 , NO2 , and O3 ) at the time of the exercise test were collected from public registers. We compared the pollutant concentrations with the proportion and severity of EIB and adjusted the analyses for air humidity and pollen counts. Pollution levels were rarely high (median PM2.5 6.0 µg/m3 , NO2 12.0 µg/m3 , and O3 47.0 µg/m3 ). The relative change in resistance at 5 Hz after exercise did not correlate with O3 , NO2 or PM2.5 concentrations (p values 0.065-0.884). In multivariate logistic regression, we compared the effects of PM2.5 over 10 µg/m³, absolute humidity (AH) over 10 g/m³ and alder or birch pollen concentration over 10 grains/m³. High (over 10 g/m3 ) AH was associated with decreased incidence (OR 0.31, p value 0.004), and PM2.5 over 10 µg/m³ was associated with increased incidence (OR 1.69, p value 0.036) of EIB. Even low PM2.5 levels may have an effect on EIB in children. Of the other properties of air, only AH was associated with the incidence of EIB.