18 Conversely in the kidney HSP inhibition or the heart, CD39 is highly expressed by the endothelium where the biological effects exert both local and systemic protective properties. The liver is distinctive in that the sinusoids contain higher numbers of resident immune mononuclear cells compared to other organs such as the heart and kidney. Beneficial effects have been also noted with adenosine-2A receptor stimulation of NKT cells in the limited lobar, warm hepatic IRI model we have used, as previously studied by Lappas and colleagues.1 This model of partial hepatic

ischemia was chosen here to minimize effects mediated by shock and secondary effects on the systemic vasculature. We were able to establish a modulatory role for NK cells in this system where regulation of IFNγ by P2 receptor responses to extracellular nucleotides appears very relevant. Other studies with IFNγ mutant mice have yielded conflicting data suggesting both beneficial and deleterious effects in IRI models. Different interferons such as interferon alpha and beta have been shown to contribute to hepatic IRI at later time points.32 Decreased injury was observed 6 hours after reperfusion in mice null for the IFNβ receptor,

but no significant differences were noted in mice null for IFNγ receptor. In our study, we noted differences at an earlier time point (3 hours) and we used NK cells from mice that have a defect in IFNγ secretion but not in IFN receptor function. Hence, our data reflect differences in release of IFNγ with Amobarbital effects Selleckchem RG7420 on recipient cells that clearly express the relevant receptors. We show that IL-12/IL-18–stimulated in vitro secretion of IFNγ by NK cells is decreased by extracellular ATPγS at low (physiologic) concentrations. Interestingly, at a higher concentration (100 μM), ATPγS again elevated levels of IFNγ secretion in wild-type NK cells. Direct toxicity or apoptosis induced in response to stimulation of P2X7 receptors was considered unlikely. First, unlike in NKT cells, the proapoptotic purinoreceptor P2X7 is not expressed in NK cells; second, cell counts were boosted by

extracellular nucleotides in a dose-dependent manner. Further, we have shown that extracellular ATP does not directly induce apoptosis in NK cells unlike in NKT cells that rapidly undergo apoptosis in response to extracellular ATP.14 In this study, we show that NK cells influence end-organ injury in hepatic IRI in a process determined by purinergic responses. Regulated pericellular ATP levels on NK cells are required for regulated IFNγ secretion and, thereby, modulation of tissue injury. Future studies will be required to dissect the relative impact of CD39 and other regulatory factors in purinergic signaling and on the other cell types involved in tissue damage and vascular injury resulting from hepatic vascular injury. Additional Supporting Information may be found in the online version of this article.