Airborne Particulates Affect Corneal Homeostasis and Immunity

PURPOSE: To determine the effects of airborne particulate matter (PM) <2.5 µm in vitro and on the normal and Pseudomonas aeruginosa (PA)-infected cornea. METHODS: An MTT viability assay tested the effects of PM(2.5) on mouse corneal epithelial cells (MCEC) and human corneal epithelial cells (HCET). MCEC were tested for reactive oxygen species using a 2′,7′-dichlorodihydrofluorescein assay; RT-PCR determined mRNA levels of inflammatory and oxidative stress markers in MCEC (HMGB1, toll-like receptor 2, IL-1β, CXCL2, GPX1, GPX2, GR1, superoxide dismutase 2, and heme oxygenase 1) and HCET (high mobility group box 1, CXCL2, and IL-1β). C57BL/6 mice also were infected and after 6 hours, the PM(2.5) was topically applied. Disease was graded by clinical score and evaluated by histology, plate count, myeloperoxidase assay, RT-PCR, ELISA, and Western blot. RESULTS: After PM(2.5) (25–200 µg/mL), 80% to 90% of MCEC and HCET were viable and PM exposure increased reactive oxygen species in MCEC and mRNA expression levels for inflammatory and oxidative stress markers in mouse and human cells. In vivo, the cornea of PA+PM(2.5) exposed mice exhibited earlier perforation over PA alone (confirmed histologically). In cornea, plate counts were increased after PA+PM(2.5), whereas myeloperoxidase activity was significantly increased after PA+PM(2.5) over other groups. The mRNA levels for several proinflammatory and oxidative stress markers were increased in the cornea in the PA+PM(2.5) over other groups; protein levels were elevated for high mobility group box 1, but not toll-like receptor 4 or glutathione reductase 1. Uninfected corneas treated with PM(2.5) did not differ from normal. CONCLUSIONS: PM(2.5) triggers reactive oxygen species, upregulates mRNA levels of oxidative stress, inflammatory markers, and high mobility group box 1 protein, contributing to perforation in PA-infected corneas.