D'Alessio, FR; Tsushima, K; Aggarwal, NR; Garibaldi, BT; Files, D; Crow, MT; King, LS
While early events in the pathogenesis of acute lung injury (ALI) have been defined, little is known about mechanisms mediating resolution. We recently found that Regulatory T cells (Tregs) play a pivotal role in lung repair by abrogating innate immune responses in the lung through the transition from injury to repair. Using a model of intratracheal lipopolysacaccharide (i.t. LPS), we also observed a marked delay in resolution of lung injury in iNOS mice as compared to wild type (WT) mice. A dichotomous response was evident: -/- following i.t. LPS early lung injury was attenuated in iNOS mice, however recovery by day 10 was markedly impaired. Compared to WT -/- mice, iNOS mice had increased mortality, persistently elevated BAL protein, albumin, cells, neutrophils and pro-inflammatory cytokines. -/- High resolution phenotype of alveolar cells by multicolor flow cytometry at intervals after i.t. LPS revealed markedly decreased numbers of Tregs, and reduced surface expression of the integrin CD103 in iNOS mice. Alveolar macrophage/monocytes expression of surface -/- molecules (Toll-like receptors, CD11b, CD14, MHC-II) dynamically changed similarly during early injury in both groups of mice. However, sustained expression of macrophage co-signalling (e.g. CD86 and CD40) molecules, critically involved in modulating immune responses, was seen in iNOS mice compared to WT mice out to day 7 after injury. Both adoptive transfer of WT iNOS bone marrow-derived -/- +/+ monocytes or direct adenoviral gene delivery of iNOS into injured iNOS mice (given as rescue therapy on days 1 and 2) restored normal -/- resolution of ALI in a pattern similar to WT. Alveolar Treg numbers increased and downregulation of macrophage CD40/CD86 expression was evident after manipulation of iNOS. In contrast, transfer of iNOS monocytes or delivery of sham adenovirus did not produce -/- resolution. Moreover, transfer of supplemental WT Tregs or antibody-mediated blockade of CD86 in injured iNOS mice restored -/- resolution of lung injury. Macrophage-derived iNOS plays a pivotal role in mediating resolution of ALI by modulating immune responses in the lung, thus facilitating clearance of alveolar inflammation and promoting lung repair. Targeting iNOS expression, particularly at later stages after onset of ALI, may prove useful as therapy to accelerate resolution in patients with ALI.
