CD163 protects against pulmonary injury and inflammation induced by acute O₃ exposure

Ozone (O₃)-driven pulmonary inflammation is partly regulated by damage associated molecular patterns (DAMPs) binding to scavenging receptors (SRs). However, how SRs and DAMPs regulate O₃-induced pulmonary inflammation remains incompletely understood. CD163 is a SR responsible for clearing cell free hemoglobin (CFH), a DAMP which accumulates during acute pulmonary injury and is associated with worsening respiratory outcomes. We hypothesized that increased CD163 is necessary for reducing CFH levels and resolving O₃-induced pulmonary injury. To test this hypothesis, we defined CD163 and CFH responses to O₃ exposure in C57BL/6N (WT) and CD163 deficient (Cd163 ^-/-) mice, as well as in human bronchoalveolar lavage fluid (BALF). In WT mice, lung Cd163 expression was significantly increased by O₃ during peak inflammation and declined 24 hours post exposure. Human exposure studies revealed a diversity of Cd163 expression and a reduction of CFH following O₃ exposure, suggesting regulation of this pathway in humans. When compared to WT mice, Cd163 ^-/- mice had augmented O₃-induced pulmonary injury, inflammation, and oxidative stress. Further, the antioxidant EUK-134 did not reduce O₃-induced pulmonary oxidative stress in Cd163 ^-/- mice, suggesting a role for CD163 in the pulmonary response to oxidative insults. Furthermore, compared to WT controls, Cd163 ^-/- mice receiving an oropharyngeal aspiration of CFH had a significant increase in airspace inflammation. Combined, these findings suggest that CD163 mediated clearance of CFH is involved in resolving O₃-induced pulmonary injury, inflammation, and oxidative stress.