Allergic airway inflammation protects against SARS-CoV-2 and MERS-CoV disease but promotes fatal SARS-CoV-1 immunopathology

A recent study has revealed that allergic asthma may provide protection against severe Coronavirus Disease 2019 (COVID-19), although the protective effects can vary depending on the specific coronavirus strain. Allergic asthma is characterized by type 2 (T2) inflammation, mucus overproduction, and airway changes. A house dust mite (HDM) respiratory exposure model was employed to investigate how pre-existing allergic inflammation impacts the progression of three highly pathogenic coronaviruses: SARS-CoV-1, SARS-CoV-2, and MERS-CoV.

Mice treated with HDM, which induces typical allergic asthma symptoms like goblet cell enlargement, increased mucus production, eosinophil migration, M2 macrophage activation, and IL-13 production, displayed lower viral loads, less weight loss, reduced lung damage, and higher survival rates across multiple SARS-CoV-2 variants. Similar protective outcomes were observed in a MERS-CoV model, with HDM-treated mice experiencing reduced mortality, lower viral levels, and diminished cytokine storm indicators.

However, the study found that allergic airway inflammation worsened SARS-CoV-1 infection. HDM-treated mice experienced severe alveolar inflammation, significant weight loss, elevated inflammatory chemicals, and higher mortality, despite having a lower viral load compared to untreated mice. This suggests that in mice, allergic airway inflammation exhibits contrasting effects on coronavirus pathogenesis, depending on the specific virus.

The findings reconcile conflicting epidemiological data and mechanistic studies across coronavirus outbreaks. The research underscores the importance of considering the host's allergic status as a crucial factor influencing disease outcomes when dealing with emerging coronaviruses.