Pulmonary Natural Killer T Cells Play an Essential Role in Mediating Hyperoxic Acute Lung Injury

Abstract

Critically ill patients are routinely exposed to high concentrations of supplemental oxygen for prolonged periods of time, which can be lifesaving in the short term, but such exposure also causes severe lung injury and increases mortality. To address this therapeutic dilemma, we studied the mechanisms of the tissue-damaging effects of oxygen in mice. We show that pulmonary invariant natural killer T (iNKT) cells are unexpectedly crucial in the development of acute oxygen-induced lung injury. iNKT cells express high concentrations of the ectonucleotidase CD39, which regulates their state of activation. Both iNKT celldeficient (Ja18 2/2) and CD39-null mice tolerate hyperoxia, compared with wild-type control mice that exhibit severe lung injury. An adoptive transfer of wild-type iNKT cells into Ja18 2/2 mice results in hyperoxic lung injury, whereas the transfer of CD39-null iNKT cells does not. Pulmonary iNKT cell activation and proliferation are modulated by ATP-dependent purinergic signaling responses. Hyperoxic lung injury can be induced by selective P2X7-receptor blockade in CD39-null mice. Our data indicate that iNKT cells are involved in the pathogenesis of hyperoxic lung injury, and that tissue protection can be mediated through ATP-induced P2X7 receptor signaling, resulting in iNKT cell death. In conclusion, our data suggest that iNKT cells and purinergic signaling should be evaluated as potential novel therapeutic targets to prevent hyperoxic lung injury.Keywords: lung injury; immunology; ATP; P2X7; oxygen High concentrations of inspired oxygen are routinely administered to critically ill patients with cardiopulmonary disease and during major surgical interventions to improve oxygen delivery to crucial organs (1). Hyperoxia-induced lung injury is caused by prolonged exposure to high oxygen concentrations (. 50%), and is typically characterized by alveolar epithelial and endothelial damage. These effects result in capillary leak syndrome, followed by inflammatory cell recruitment (2-5).Recently, hyperoxia and its potential for organ injury have received more attention in the clinical literature (6). Little is currently known about pulmonary immune defense mechanisms to hyperoxia in vivo. In addition, no therapeutic strategies are available to control pathophysiological processes in hyperoxic lung injury.Invariant natural killer T (iNKT) cells bridge innate and adaptive immune responses. These cells are characterized by their ability to use invariant T-cell receptors to recognize glycolipid antigens presented by CD1d, leading to a rapid cytokine effector response (7,8). Although the lung itself does not carry an exceptionally large population of iNKT cells, this does appear to be a site where iNKT cells can exert profound effects (9). CD39, also known as ectonucleoside triphosphate diphosphohydrolase-1, hydrolyzes ATP and ADP to adenosine monophosphate (AMP), catalyzed by CD73, also known as 59-nucleotidase, to form adenosine (10, 11). CD39 is highly expressed in iNKT cells (12). CD39 deficiency has mainly ...

Lysophosphatidic acid generation by pulmonary NKT cell ENPP-2/autotaxin exacerbates hyperoxic lung injury

“…ENPP-2 is up-regulated in hyperoxia-exposed pulmonary iNKT cells on a transcriptional level Pulmonary NKT cells were harvested, cultured, and exposed to 95 % oxygen/5 % CO 2 for 72 h as described [7]. RT-PCR analysis revealed a significant and approximately 20-fold upregulation of the ectonucleotide pyrophosphatase/ phosphodiesterase 2 (Autotaxin, ENPP-2) on the NKT cells after exposure to hyperoxia when compared to NKT cells exposed to room air (p<0.01) (Fig.…”

“…5a). CD3/NK1.1 double intermediate positive cells were defined as iNKT cells as previously described [7]. After 72 h of 100 % exposure, animals show significant increases of iNKT cells compared to their baseline (0.23 versus 4.7 % of all pulmonary mononuclear cells) (Fig.…”

“…Pulmonary mononuclear cells (PMNs) were extracted and stained with PE-conjugated anti-GR-1 and FITCconjugated anti-F4/80. PMNs were defined as GR-1+/F4/80-cells [7].…”

“…Different lung disease models such as asthma and more recently hyperoxia-induced lung injury could be linked to NKT cell-induced immune responses [1,[3][4][5][6][7]. Hyperoxia remains a mainstay in clinical patient care in order to improve oxygen delivery to crucial organs in critically ill patients suffering from acute lung injury or during cardiac surgery to name a few [3].…”

“…Hyperoxia-exposed wild type mice developed severe lung injury with pulmonary NKT cell proliferation and showed a nearly 100 % mortality rate after 72 h while CD39 deficient animals survived with low NKT cell proliferation and significantly less lung injury [7]. The mechanism as to how NKT cells undergo activation and exhibit these detrimental effects in hyperoxic injury remains unclear.…”