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

BACKGROUND

Air pollution, specifically fine particulate matter (PM), in China is responsible for millions of excess deaths each decade. Examinations of Chinese municipalities have revealed correlations between ambient PM levels and the prevalence and severity of respiratory viral infections. Seasonal sources of ambient PM vary, with coal combustion for indoor heating significantly contributing during colder months. Due to this seasonality, we sought to investigate whether exposure to seasonal PM 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 PM samples were chemically analyzed, HNECs collected from males (N = 4) and females (N = 3) grown at air-liquid interface were exposed to 22 μg/cm of seasonal PM 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.

RESULTS

Summer and fall PM 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 PM 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 PM samples without infection induced a moderate transcriptional response at 2 h, with the winter PM inducing the greatest response. The seasonal PM exposures followed by viral infection resulted in a more robust transcriptional response at 2 h p.i. with the winter, spring, and fall PM samples (but not the summer PM) upregulating many inflammatory pathways. At 24 h p.i., only the spring PM sample increased inflammatory and antiviral mediator proteins in the basolateral medium, while winter PM increased these inflammatory markers in the mock infected cultures.

CONCLUSIONS

Chemical differences in seasonal PM 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.