Nitrogen dioxide pollution increases vulnerability to COVID-19 through altered immune function

Abstract

Previous ecological studies suggest the existence of possible interplays between the exposure to air pollutants and SARS-CoV-2 infection. Confirmations at individual level, however, are lacking. To explore the relationships between previous exposure to particulate matter < 10 μm (PM₁₀) and nitrogen dioxide (NO₂), the clinical outcome following hospital admittance, and lymphocyte subsets in COVID-19 patients with pneumonia. In 147 geocoded patients, we assessed the individual exposure to PM₁₀ and NO₂ in the 2 weeks before hospital admittance. We divided subjects according to the clinical outcome (i.e., discharge at home vs in-hospital death), and explored the lymphocyte-related immune function as an index possibly affecting individual vulnerability to the infection. As compared with discharged subjects, patients who underwent in-hospital death presented neutrophilia, lymphopenia, lower number of T CD45, CD3, CD4, CD16/56 + CD3 + , and B CD19 + cells, and higher previous exposure to NO₂, but not PM₁₀. Age and previous NO₂ exposure were independent predictors for mortality. NO₂ concentrations were also negatively related with the number of CD45, CD3, and CD4 cells. Previous NO₂ exposure is a co-factor independently affecting the mortality risk in infected individuals, through negative immune effects. Lymphopenia and altered lymphocyte subsets might precede viral infection due to nonmodifiable (i.e., age) and external (i.e., air pollution) factors. Thus, decreasing the burden of air pollutants should be a valuable primary prevention measure to reduce individual susceptibility to SARS-CoV-2 infection and mortality.

Keywords: Air pollution; COVID-19; Elderly; Lymphocyte subsets; Lymphocytes; Mortality; NO2; PM10; SARS-CoV-2.

Fig. 1

Average daily air concentrations of PM₁₀ and NO₂ during the 2 weeks preceding the day of hospital admittance in COVID-19 patients admitted for pneumonia, who underwent in-hospital death or discharge at home. Patients were geocoded based on the residential address. The exposure to PM₁₀ and NO₂ before hospital admittance was assessed, for each subject, in the specific living area. Asterisk indicates P = 0.04

Fig. 2

Odds ratios and 95% confidence interval (CI) for the association between average air concentrations of PM₁₀ and NO₂ in the 2 weeks before hospital admittance and in-hospital COVID-19 death, adjusted for age, sex, and presence of comorbidities, as covariates