Conversion from resistance to susceptibility: a dirty trick by PM10

The results of whole-body exposure to airborne particulate matter <10 µm on the cornea of BALB/c mice, how their natural resistance to Pseudomonas aeruginosa (PA) keratitis is impacted, and whether plastoquinonyl-decyl-triphenylphosphonium (SKQ1) is protective were examined. Control or PM10 exposure was performed for 2 weeks; corneal sensitivity, tear production, and Langerhans cell (LC) number were determined; and reverse transcription PCR (RT-PCR) was performed. After exposure, infection with PA, and topical treatment with PBS or SKQ1, clinical score, slit lamp, polymorphonuclear cells (PMN) quantitation, bacterial count, RT-PCR, Western blot, and flow cytometry were performed. PM10-exposed corneas showed significantly increased corneal sensitivity, decreased tear production, and a significant increase in conjunctival LC vs. control exposed eyes. PM10 exposure significantly increased mRNA for proinflammatory cytokines and significantly decreased them for glutathione peroxidase 4 and Nrf2. Disease severity after PM10 exposure was significantly increased at 3 and 5 dpi and resulted in higher plate counts and PMN numbers in the cornea at 5 dpi. Corneal mRNA levels after infection showed a similar pattern to the uninfected cornea after PM10 exposure and were selectively confirmed by Western blot. Flow cytometry showed increases in macrophages and T cells in the cornea after infection following PM10 exposure. SKQ1 significantly improved disease at both 3 and 5 dpi, restored mRNA and protein to control levels, reduced corneal bacteria and PMN number, and prevented increased sensitivity and tear reduction. Whole-body exposure to PM10 resulted in converting BALB/c mice that exhibit genetic resistance to a susceptible phenotype in response to PA and SKQ1 reversed the majority of these effects and restored resistance.