Grethe Elholm

The Danish urban–rural gradient of allergic sensitization and disease in adults

The reported prevalence of allergic sensitization among children is lower in rural areas than in urban areas of the world. The aim was to investigate the urban–rural differences of allergic sensitization to inhalant allergens in adults depending on childhood exposure living in an industrialized country as Denmark.

The cohort of young Danish farmers - A longitudinal study of the health effects of farming exposure.

Working in agriculture poses a serious risk for development of respiratory diseases, especially when working in animal housing. Animal workers are exposed to a mixture of organic and inorganic dust together with fumes and gases, including allergens and microbial-associated molecular patterns with a potentially major impact on respiratory health and the immune system. Exposure to microbial agents in animal housing is associated with an increased prevalence of respiratory symptoms, including bronchial hyperresponsiveness, accelerated lung function decline, and neutrophil-mediated inflammation. These clinical findings are often seen without IgE-mediated sensitization. In fact it has been found in recent studies that the prevalence of atopic sensitization and atopic asthma is low among farmers compared with other populations. The SUS study was designed to identify the type and occurrence of respiratory symptoms and disease, and to investigate risk factors for respiratory disorders and changes in lung function among young farming students. The cohort of young Danish farmers was established in 1992/1994 and followed up in 2007/2008 with a participation rate of 51.7%. The cohort consists of 1734 male farming students, 230 female farming students, and 407 army recruits as controls.

Become a farmer and avoid new allergic sensitization: Adult farming exposures protect against new-onset atopic sensitization

cutoffs. Furthermore, although blood eosinophil levels are suggested to be useful biomarkers contributing to the characterization of subphenotypes of asthma, they poorly predict sputum eosinophil levels. Similarly, the more sensitive but less specific cutoff of 0.35 kU/L for atopy may result in children without active allergic inflammation to be classified as atopic. In addition, atopy may not be causally related to wheeze even if temporality is established, which is reflected in population-attributable risk proportions around 60%. Moreover, there is evidence that suggests that different sensitization patterns drive different phenotypes of wheeze or asthma and differential effects of eosinophil levels on asthma over time during childhood have been described. However, atopy and eosinophil levels were assessed only once and for atopy a limited number of allergens were tested, both precluding the exploration of sophisticated patterns. Likewise, because of the exclusion of children who had wheeze or asthma at baseline, analyses were restricted to late-onset wheeze, which has a stronger association with atopy than does early-onset persistent wheeze. Nonetheless, increased wheeze incidence in both atopic groups—low and high eosinophil levels—would not explain the discrepancy in the interaction measures between asthma at baseline and during follow-up. In conclusion, the detected synergistic interaction provides evidence that atopy and eosinophils act through a common causal pathway in the pathogenesis of childhood wheeze. Both biomarkers may be useful for predicting and phenotyping childhood wheeze in clinical routine, but special care should be devoted to patterns and levels of atopic sensitization and blood eosinophils.

Exposure levels, determinants and IgE mediated sensitization to bovine allergens among Danish farmers and non-farmers

BACKGROUND Bovine allergens can induce allergic airway diseases. High levels of allergens in dust from stables and homes of dairy farmers have been reported, but sparse knowledge about determinants for bovine allergen levels and associations between exposure level and sensitization is available. OBJECTIVE To investigate levels and determinants of bovine allergen exposure among dairy, pig and mink farmers (bedroom and stable), and among former and never farmers (bedroom), and to assess the prevalence of bovine allergen sensitization in these groups. METHODS In 2007-2008, 410 settled dust samples were collected in stables and in bedrooms using an electrostatic dust-fall collector over a 14 day period among 54 pig farmers, 27 dairy farmers, 3 mink farmers as well as 71 former and 48 never farmers in Denmark. For farmers sampling was carried out both during summer and winter. Bovine allergen levels (μg/m(2)) were measured using a sandwich ELISA. Determinants for bovine allergen exposure in stables and bedrooms were explored with mixed effect regression analyses. Skin prick test with bovine allergen was performed on 48 pig farmers, 20 dairy farmers, 54 former and 31 never farmers. RESULTS Bovine allergen levels varied by five orders of magnitude, as expected with substantially higher levels in stables than bedrooms, especially for dairy farmers. Bovine allergen levels in bedrooms were more than one order of magnitude higher for dairy farmers compared to pig farmers. Former and never farmers had low levels of bovine allergens in their bedroom. Bovine allergen levels during summer appeared to be somewhat higher than during winter. Increased bovine allergen levels in the bedroom were associated with being a farmer or living on a farm. Mechanical ventilation in the bedroom decreased bovine allergen level, significant for dairy farmers β=-1.4, p<0.04. No other significant effects of either sampling or residence characteristics were seen. Allergen levels in dairy stables were associated to type of dairy stable, but not to other stable or sampling characteristics. Sensitization to bovine allergens was only found in one pig farmer. CONCLUSION This study confirms high bovine allergen levels in dairy farms, but also suggests sensitization to bovine allergens among Danish farmers to be uncommon. Furthermore the importance of a carrier home effect on allergen load is emphasized. Whether the risk for bovine sensitization is related to the allergen level in the stable or the dwelling remains to be determined.

The effect of occupational farming on lung function development in young adults: a 15-year follow-up study

Objectives Longitudinal studies on the effect of farming on lung function in young participants are few. Our objective was to explore if exposure to farming impaired lung function in young adults. Methods We studied 1964 farming students and 407 controls in 1992/2004, and carried out follow-up in 2007/2008. Spirometry, skin prick test and bronchial hyper-responsiveness (BHR) were assessed, height and weight measured, and questionnaires covering health and occupation were collected. Cumulative dust and endotoxin exposures were estimated from modelled personal dust measurements. Lung function effect was expressed as change in z-score during follow-up using the Global Lung Initiative 2012 project prediction equations. Longitudinal data were available for 1134 young participants ≤25 years at baseline. Results We found no differences in lung function Δz-scores between farmers and controls, however, adjusted multivariable linear regression showed a negative effect among current farmers on ΔzFEV1 (forced expiratory volume in 1 s; −0.12, p=0.006) and ΔzFEV1/FVC (forced vital capacity; −0.15, p=0.009) compared to ex-farmers. An interaction was found between sex and farming, showing that current farming suppresses ΔzFEV1 and ΔzFVC more among females. Smoking in farmers had a deleterious effect on ΔzFEV1, which was not seen in controls, though no significant interaction was found. Farm upbringing protected against impairment of lung function, and BHR at baseline had a deleterious effect on ΔzFEV1 only in those not raised on a farm. Conclusions We conclude that being a current farmer is associated with a negative effect on lung function, when compared to ex-farmers, with females being more susceptible. Being raised on a farm protects against the adverse effect of BHR on change in lung function.

High exposure to endotoxin in farming is associated with less new-onset pollen sensitisation

Objectives Little is known about risk factors for new onset and loss of atopic sensitisation in adulthood. The aim is to examine the longitudinal effect of quantitatively assessed endotoxin exposures on changes in specific allergen sensitisation in young adults. Methods The cohort consisted of 1113 young Danish farmers and rural controls, with a mean age of 19 years at baseline. Sensitisation to birch pollen, grass pollen, cat dander and house dust mite was measured by specific IgE levels in serum samples from baseline and at 15 years’ follow-up. Changes in sensitisation were analysed in relation to cumulative endotoxin exposure during follow-up, considering early life farm exposure. Results Endotoxin exposure during follow-up was significantly associated with less new onset of specifically grass and birch pollen sensitisation. For the highest versus lowest quartile of cumulative endotoxin exposure, the OR for new-onset IgE sensitisation was 0.35 (0.13–0.91) for birch and 0.14 (0.05–0.50) for grass. On the other hand, loss of pollen sensitisation showed a positive, although mostly non-significant, association with increased levels of endotoxin exposure. Endotoxin exposure was not associated with significant changes in cat dander and house dust mite sensitisation. Conclusions High exposure to endotoxin during young adulthood appears to protect against new onset of pollen sensitisation, independent of childhood farm exposure.

Pig Farmers’ Homes Harbor More Diverse Airborne Bacterial Communities Than Pig Stables or Suburban Homes

Airborne bacterial communities are subject to conditions ill-suited to microbial activity and growth. In spite of this, air is an important transfer medium for bacteria, with the bacteria in indoor air having potentially major consequences for the health of a building’s occupants. A major example is the decreased diversity and altered composition of indoor airborne microbial communities as a proposed explanation for the increasing prevalence of asthma and allergies worldwide. Previous research has shown that living on a farm confers protection against development of asthma and allergies, with airborne bacteria suggested as playing a role in this protective effect. However, the composition of this beneficial microbial community has still not been identified. We sampled settled airborne dust using a passive dust sampler from Danish pig stables, associated farmers’ homes, and from suburban homes (267 samples in total) and carried out quantitative PCR measurements of bacterial abundance and MiSeq sequencing of the V3–V4 region of bacterial 16S rRNA genes found in these samples. Airborne bacteria had a greater diversity and were significantly more abundant in pig stables and farmers’ homes than suburban homes (Wilcoxon rank sum test P < 0.05). Moreover, bacterial taxa previously suggested to contribute to a protective effect had significantly higher relative and absolute abundance in pig stables and farmers’ homes than in suburban homes (ALDEx2 with P < 0.05), including Firmicutes, Peptostreptococcaceae, Prevotellaceae, Lachnospiraceae, Ruminococcaceae, Ruminiclostridium, and Lactobacillus. Pig stables had significantly lower airborne bacterial diversity than farmers’ homes, and there was no discernable direct transfer of airborne bacteria from stable to home. This study identifies differences in indoor airborne bacterial communities that may be an important component of this putative protective effect, while showing that pig stables themselves do not appear to directly contribute to the airborne bacterial communities in the homes of farmers. These findings improve our understanding of the role of airborne bacteria in the increasing prevalence of asthma and allergy.

Inhalation of House Dust and Ozone Alters Systemic Levels of Endothelial Progenitor Cells, Oxidative Stress, and Inflammation in Elderly Subjects

Ambient air pollution including ozone and especially particulate matter represents important causes of cardiovascular disease. However, there is limited knowledge on indoor air dust with respect to this risk and the potential interactions between dust and ozone. Here, we exposed 23 healthy elderly subjects for 5.5 h, to either clean air, house dust at 275 µg/m3 (diameter < 2.5 µm), ozone at 100 ppb or combined house dust and ozone in a double-blinded randomized cross-over study. The combined house dust and ozone exposure was associated with a 48% (95% CI 24%-65%) decrease as compared with the clean air exposure, in CD34+KDR+ late endothelial progenitor cells (EPCs) per leukocyte in the blood shortly after exposure, whereas none of the single exposures resulted in a significant effect. The combined exposure also increased reactive oxygen species production capacity in granulocytes and monocytes as well as an up-regulation of interleukin-8 mRNA levels in leukocytes. Ozone alone reduced the gene expression of tumor necrosis factor and C-C motif chemokine ligand 2, while dust alone showed no effects. The combined exposure to house dust and ozone also reduced levels of oxidized purines in DNA consistent with concomitant up-regulation of mRNA of the repair enzyme 8-oxoguanine DNA glycosylase. The reduction in late EPCs can be an indicator of cardiovascular risk caused by the combination of pulmonary oxidative stress induced by ozone and the inflammatory potential of the house dust. These data were corroborated with in vitro findings from exposed human macrophages and endothelial cells.

Adult farming exposure does not protect against sensitization to the storage mite Lepidoglyphus destructor

To the Editor, Storage mite infestations are common in grain, straw, and hay storages. Sensitization and allergy to storage mites have been found primarily in occupationally exposed individuals such as farmers, millers, and grain and also meat production workers where storage mite exposure is high. Growing up in a farm environment, however, is a well‐established protective factor against atopic sensitization to common allergens. Working as a farmer in young adulthood may also provide protection against incident sensitization and persistence of existing sensitization, especially to pollen allergens. As storage mites are most abundant in barns and stables, we assume that adults working in farming are exposed to much higher levels of storage mite allergens than children growing up in farm homes, with an at highest intermittent presence in barns and stables. However, it is so far unknown whether and how early‐life and adult farming exposures affect specific storage mite sensitization over time. As far as we are aware, we here present the first longitudinal data on new‐onset and loss of sensitization to the storage mite Lepidoglyphus destructor (Lep d). The change in Lep d sensitization in relation to farming exposure and elevated Lep d concentrations was examined in a cohort of 1166 young Danish farmers and controls, with a mean age of 19 years at baseline. Baseline data were collected between 1992 and 1994 and at follow‐up approximately 14 years later. Sensitization to Lep d was measured by specific IgE (sIgE) levels and skin prick test (SPT) at both baseline and follow‐up. Serum was stored at −80°C, and baseline and follow‐up sera were tested simultaneously in IgE duplex analyses (carried out at ALK Abello), to minimize interassay and day‐to‐day variation. A positive specific IgE response was defined as ≥0.35 kU/L, and a positive SPT response was defined as a mean wheal reaction ≥3 mm in the presence of a negative control. Changes in sensitization (new‐onset and loss) were analyzed in relation to farm exposure using self‐reported information on exposures, as well as quantitative estimates of dust and endotoxin exposures based on actual personal exposure measurements. The thus modeled dust and endotoxin exposure levels were in this study also used as surrogates for the lifetime levels of exposure to barns and animal stables where levels of Lep d and other storage mites are known to be high. New‐onset sensitization was defined as negative at baseline and positive at follow‐up, and loss of sensitization was defined as positive at baseline and negative at follow‐up. Childhood exposure was categorized as having grown up in an urban environment, in the countryside but not on a farm, or on a farm with animals. Farmwork during the follow‐up period was categorized as “never,” “ex‐,” or “current farmer” with participants leaving farming during the follow‐ up period categorized as ex‐farmers, and those still working as farmers at follow‐up as “current farmers.” Animal husbandry was subdivided into four exposure groups of “no animals,” “swine,” “cattle,” and “mixed swine and cattle.” Dust and endotoxin exposure was measured in a subpopulation, and the results were used in combination with detailed work diaries to estimate the cumulative exposure for all study participants. Analyses were based on exposure quartiles, the 4th quartile representing the highest exposure. Changes in sensitization in relation to farm exposures during follow‐up were analyzed by logistic regression to compare the participants with new‐onset sensitization with those never sensitized, and those who lost sensitization with the participants with persistent Lep d sensitization. Changes in sensitization in relation to endotoxin exposures were also analyzed by logistic regression models adjusted for farm childhood, pet‐keeping during childhood and smoking status. At baseline, the Lep d sensitization prevalence was 4.9% measured by SPT and 6.1% measured by sIgE. At follow‐up, the Lep d sensitization prevalence was 13.5% measured by SPT and 5.9% measured by sIgE. The unadjusted odds ratios in Table 1 show less new‐ onset sensitization to Lep d among participants with a rural or farm childhood and a greater loss of sensitization consistent with findings for other aeroallergens. In contrary, farming exposure during adulthood appeared to be consistently associated with increased new‐ onset Lep d sensitization and with less loss of sensitization, although rarely significant due to low numbers. Significantly less loss of sensitization was observed particularly for work with swine and for high dust and endotoxin exposure. Adjusted analyses of endotoxin exposure confirmed that an exposure environment with moderate and high endotoxin exposure, and presumably paralleled by an elevated Lep d exposure, was associated with increased new‐onset sensitization to Lep d and significantly less loss of Lep d IgE sensitization independent of childhood exposure (Figure 1 for IgE test results; Figure S1 shows the results of the adjusted SPT analyses). We previously showed that current farming exposure was protective against new pollen sensitization. This protective effect was, however, not seen for HDM, but neither was an increased risk of new HDM sensitization among current farmers, as now suggested for Lep d sensitization. General storage mite sensitization levels may Abbreviations: CI, confidence interval; HDM, house dust mite; IgE, immunoglobulin E; kU/ L, kilo units per liter; OR, odds ratio; SPT, skin prick test. DOI: 10.1111/all.13533

Endotoxins, Glucans and Other Microbial Cell Wall Agents

During the last decades an increasing interest in microbial cell wall agents has been established, since exposure to these agents has been linked to a wide range of adverse and beneficial health effects. The term microbial cell wall agents refers to a group of molecules of different composition that are integral structural components of microorganisms like gram-negative and gram positive bacteria and fungi. The available information on exposure characteristics for these cell wall agents within indoor environments and their associated health effects is summarized in this chapter.