IL-9 identified as contributor to viral spread and airway inflammation in COVID-19

In a recent study published in Nature Communicationresearchers used a K18-hACE2 (ACE2.Tg) transgenic mouse model to demonstrate that interleukin-9 (IL-9) plays a crucial role in the pathogenesis of coronavirus disease 2019 (COVID-19).

It evolves transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and subsequent inflammation of the airways due to viral infection.

Study: IL-9 worsens SARS-CoV-2 infection and exacerbates associated airway inflammation. Image Credit: MarynaOlyak/Shutterstock.com

Background

SARS-CoV-2 infection could induce acute respiratory distress syndrome (ARDS), a life-threatening condition resulting from hyperactivation of immune cells that triggers bronchoalveolar inflammation, inflammatory cascade and immunopathology related to COVID-19 .

Thus, anti-inflammatory drugs, such as dexamethasone, could reduce the severity of COVID-19-induced respiratory symptoms and reduce mortality. In general, immunosuppression is an effective tool for COVID-19 mitigation, at least against COVID-19 lung pathologies.

Il-9 is a gamma (γ) chain family cytokine primarily produced by Th9 cells, a CD4+ subpopulationT cells. A key transcription factor, Pu.1 is essential for IL-9 induction and Th9 cell differentiation. Forkhead Box Protein O1 (Foxo1) is another essential transcription factor for the induction of IL-9 in Th cells.

IL-9 promotes mast cell growth and plays a role in allergic inflammation. Likewise, its role in severe airway inflammation and bronchial hyperresponsiveness caused by respiratory syncytial virus (RSV) infection and asthma is well recognized.

However, scientists have not yet discovered the role of IL-9 in the immunopathology associated with SARS-CoV-2.

About the study

The current study used six- to eight-week-old male and female hACE2.Tg mice to administer live SARS-CoV-2 and perform all study experiments. They co-hosted infected mice with the uninfected ACE2.Tg mice in a 1:1 ratio 24 hours post-infection (pi) to monitor the mice for COVID-19 symptoms and measure their other parameters.

The researchers used samples of lung tissue and feces from all animals tested to measure viral loadthat is, the relative number of SARS-CoV-2 ribonucleic acid (RNA) copies and their relative gene expression.

While they were using Foxo1in/in mice to study the role of IL-9, bronchoalveolar lavage fluid (BALF) from the lungs of test animals helped them quantify IL-4/9/10 and interferon-gamma (IFN-γ ) by enzyme immunoassay (ELISA).

In addition, the team used peripheral blood mononuclear cells (PBMC) from healthy human donors to isolate RNA and test the expression of the respective genes against β-actin by reverse transcription-polymerase chain reaction ( RT-PCR).

The team then normalized the relative gene expression levels by log2 transformation to calculate Z-scores. Finally, they plotted the median of the log2-transformed relative gene expression Z-scores as a heat map.

In a substudy, the team randomly selected five mice to assess the comparative therapeutic effects of vehicle, remdesivir (RDV), or Foxo1 inhibitors. In another substudy, they examined the therapeutic effects of suboptimal αIL-9 and RDV (SO) when given once daily by intraperitoneal injection.

Results

So far, studies have not deciphered whether adaptive immune cells, particularly CD4+ and CD8+ T cells, regulate the anti-SARS-CoV-2 response and airway inflammation despite conferring protection against primary infection with SARS-CoV-2.

In this study, the researchers demonstrated that the Foxo1-The IL-9 axis controlled two distinct pathological features of COVID-19 – namely, the antiviral pathway and airway inflammation.

Accordingly, they noted that IL-9 was upregulated in ACE2.Tg mice infected with SARS-CoV2, whereas its depletion enhanced viral clearance by regulating airway inflammation and lung pathology induced by SARS-CoV-2.

Previous studies have also established that IL-9 triggers mast cell hyperplasia and mucus production. Thus, anti-IL-9 neutralization decreases allergic inflammation.

Consistent with these findings, the results of the current study showed that stopping IL-9 neutralization in SARS-CoV-2 infected animals could help reduce histopathological scores and decrease the collagen deposition, mucus production and mast cell accumulation in the lungs of all animals tested.

Together, these data indicated that IL-9 and mast cells interact during SARS-CoV-2 infection, consistent with previous findings that IL-9 promotes mastocytosis.

In addition, study data demonstrated that Foxo1 deficiency in CD4+ T cells blunted IL-9 production, which made test animals less susceptible to infection with SARS- CoV-2 and virus-induced airway inflammation.

Curiously, exogenous transfer of IL-9 into Foxo1-sufficient CD4+ T cells rendered Foxo1-deficient mice susceptible to SARS-CoV-2 infection, further confirming that Foxo1-The specific Th cell pathway mediated by IL-9 played a role in the pathogenesis of COVID-19.

conclusion

Collectively, the current study provided much-needed mechanistic insights into important pro-inflammatory pathways involved in SARS-CoV-2 infection and presented proof-of-principle that IL-9-directed therapeutics could help mitigate the severity of COVID-19, especially pulmonary complications due to SARS-CoV-2 infection.