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Relation
Gilles S, Blume C, Wimmer M, et al. Pollen pollution weakens the innate defense against respiratory viruses.allergy. 2020;75(3):576-587.
Draft
A three-part study that combined data from human cell cultures, mouse models, and human cohorts to test the authors' hypothesis that pollen exposure weakens immune defenses against viral infections
Participant
The human portion of this study consisted of several parts, including both prospective observational and interventional controlled experiments, along with a large retrospective study. The researchers recruited healthy people for the observation and intervention partsnot allergicvolunteers in Augsburg, Germany, and enrolled them into multiple cohorts. Eight participants were monitored for symptom intensity during the 2016 allergy season to measure community exposure to birch pollen. The researchers recruited 2 groups of 9 participants each (again, non-allergic subjects) as an experimental group to be either exposed to pollen or a control group to be treated with placebo.
The retrospective human study examined nasal swabs from 20,062 participants collected from 2010 to 2013 at Sahlgrenska University Hospital in Gothenburg, Sweden. This final cohort included all ages, including children. The paper did not provide further demographic details for these participants.
In vitro part
For the cell culture portion of the research, primary bronchial epithelial cells were obtained from healthy individuals using bronchoscopy and expanded in suitable growth media and induced to differentiate. Nasal epithelia were also obtained from healthy volunteers undergoing nasal surgery or from nasal brush biopsies and cultured in appropriate media.
In vivo part
Six-week-old female mice were used in the initial ex vivo portion of the experiments.
Study intervention
In the small experimental human study, the 18 subjects underwent 3 nasal washes with either a placebo of saline or birch pollen extract (n = 9). Unilateral curettage biopsies were taken before and after the study. Eight participants were screened for sustained environmental exposure to pollen in the same community as the intervention and control cohorts.
In vitro part
The cultured bronchial and epithelial tissues were stimulated with pollen extracts and then exposed to human rhinovirus 16 (RV16) virus cultures.
In vivo part
Six-week-old female mice were infected with respiratory syncytial virus (RSV) and then exposed to ragweed pollen by intranasal instillation for 3 consecutive days.
Results
Observation group
Among the 20,062 participants from Gothenburg, 5,782 rhinovirus‐positive cases occurred during the allergy season over a 3‐year period. In these human subjects, nasal symptoms were positively correlated with the abundance of birch pollen in the air. Time series analyzes revealed a significant correlation between rhinovirus‐positive cases, airborne birch pollen concentrations, and precipitation (P=0.005). There was a positive nonlinear relationship between rhinovirus and pollen when comparing RSV cases with pollen counts, while the association between rhinovirus/pollen and precipitation was negative. (In other words, when it rained and pollen concentrations decreased, the risk of RSV cases decreased rather than increased.)
Interventional group
Data from 8 non-allergic volunteers who tracked their symptoms in 2016 was used to determine that their nasal symptoms correlated with pollen concentrations. Time series analysis revealed a significant cross-correlation between nasal symptoms and birch pollen with a lag effect of up to 9 days, although the strongest correlation of symptoms was with pollen concentrations the previous day. In the 9 volunteers directly challenged with birch pollen, exposure resulted in downregulation of type I and III interferons in the nasal mucosa compared to those treated with saline.
In vitro and in vivo results
In the culture and animal parts of this study, pollen exposure significantly reduced interferon-λ and pro-inflammatory chemokine responses of airway epithelia to rhinovirus and viral mimetics and reduced nuclear translocation of interferon regulatory factors. In RSV-infected mice, simultaneous exposure to pollen attenuated the expression of antiviral genes and increased pulmonary virus titers.
Key point
In non-allergic human subjects, nasal symptoms were positively correlated with the abundance of airborne birch pollen, and nasal birch pollen exposure resulted in downregulation of type I and III interferons in their nasal mucosa. In the large patient cohort, the number of rhinovirus-positive cases was correlated with airborne birch pollen concentrations.
Clinical implications
This combination of tissue culture, mouse and human data provides a compelling argument that pollen exposure weakens innate immune defenses against viral infections. What's particularly important is that the participants in this study were not allergy sufferers - meaning these results apply to everyone, not just sensitive people. Pollen concentrations vary seasonally, of course, and we are generally alerted to these concentrations by people who are showing symptoms. Pollen concentrations are also carefully monitored by health authorities, and these levels can be easily accessed online by either the government or the government (link removed). Knowing that rising pollen levels may make us more vulnerable to viral infections is particularly important this year during the Covid-19 pandemic.
A message broadcast by Radio Sweden on March 29, 2020, quotes one of the authors of this study, Dr. Åslög Dahl, who heads the pollen laboratory at the University of Gothenburg. She has announced preliminary results of a new study. Using Covid-19 data from the World Health Organization, "Dahl says areas with the highest death rates from the coronavirus have also been shown to have the highest pollen levels." Although she points out that these results were hastily compiled and need further study, Dahl suggests that everyone - whether they have allergies or not - should currently follow the advice given to people who are sensitive to pollen and allergies.
This is best summarized in the paper's abstract: "The ability of pollen to suppress innate antiviral immunity independent of allergy suggests that high-risk populations should avoid extensive outdoor activities when pollen and respiratory virus seasons coincide."
Although the observation of Covid-19 rates with pollen counts is still preliminary, together with this current study it is convincing enough that we should encourage patients to follow it. There is no risk of reducing pollen levels.
(link removed) gives allergy sufferers this tip:
- Bleiben Sie an trockenen, windigen Tagen im Haus. Die beste Zeit, um nach draußen zu gehen, ist nach einem guten Regen, der hilft, Pollen aus der Luft zu entfernen.
- Delegieren Sie Rasenmähen, Unkrautjäten und andere Gartenarbeiten, die Allergene hervorrufen.
- Ziehen Sie die Kleidung aus, die Sie draußen getragen haben, und duschen Sie, um Pollen von Ihrer Haut und Ihren Haaren zu spülen.
- Hängen Sie keine Wäsche draußen auf – Pollen können an Laken und Handtüchern haften bleiben.
- Tragen Sie eine Pollenmaske, wenn Sie im Freien arbeiten.
If the results of this study hold up to further validation, the advice for allergy sufferers may apply to everyone, especially during a viral infection outbreak.