# Seasonal PM 2.5 exposures induce differential responses to influenza A virus infection in primary human airway epithelial cells

## TL;DR

This study shows that seasonal variations in PM2.5 pollution affect how human airway cells respond to influenza infection, with winter and spring pollution increasing inflammation.

## Contribution

The study reveals that seasonal PM2.5 chemical composition alters the host's antiviral and inflammatory response to influenza in a sex-dependent manner.

## Key findings

- Winter PM2.5 induced the strongest transcriptional response in nasal epithelial cells.
- Exposure to winter, spring, and fall PM2.5 increased inflammatory pathways after influenza infection.
- Spring PM2.5 increased inflammatory and antiviral proteins in the basolateral medium at 24 h post-infection.

## Abstract

Air pollution, specifically fine particulate matter (PM2.5), in China is responsible for millions of excess deaths each decade. Examinations of Chinese municipalities have revealed correlations between ambient PM2.5 levels and the prevalence and severity of respiratory viral infections. Seasonal sources of ambient PM2.5 vary, with coal combustion for indoor heating significantly contributing during colder months. Due to this seasonality, we sought to investigate whether exposure to seasonal PM2.5 collected in Xinxiang, China would differentially alter the response to subsequent influenza A/California/04/2009 (H1N1) viral infection in a primary human nasal epithelial cell (HNEC) culture model. After the PM2.5 samples were chemically analyzed, HNECs collected from males (N = 4) and females (N = 3) grown at air-liquid interface were exposed to 22 μg/cm2 of seasonal PM2.5 followed by inoculation with influenza A H1N1 at MOI = 0.001. At 2 and 24 h post infection (p.i.) we assessed transcriptional changes and basolateral release of immune and antiviral mediators.

Summer and fall PM2.5 samples contained a greater organic carbon mass fraction compared to winter and spring. Winter contained the largest mass fraction of anionic components and spring the largest inorganic element mass fraction. In response to infection alone without PM2.5 exposure, the transcriptional response to infection at 24 h p.i. differed between the sexes with males having more robust interferon pathway activation. Exposure to the seasonal PM2.5 samples without infection induced a moderate transcriptional response at 2 h, with the winter PM2.5 inducing the greatest response. The seasonal PM2.5 exposures followed by viral infection resulted in a more robust transcriptional response at 2 h p.i. with the winter, spring, and fall PM2.5 samples (but not the summer PM2.5) upregulating many inflammatory pathways. At 24 h p.i., only the spring PM2.5 sample increased inflammatory and antiviral mediator proteins in the basolateral medium, while winter PM2.5 increased these inflammatory markers in the mock infected cultures.

Chemical differences in seasonal PM2.5 from the winter, spring, and fall, coinciding with influenza season, likely contribute to the adjuvant pro-inflammatory effects of exposure on antiviral host response. Heightened inflammation early in infection could contribute to worsened pathogenesis.