2D). However, similar reduction was observed in TNF-α secretion (Fig. 2E), suggesting that the slight reduction in IL-1β secretion in Pkr−/− macrophages is not related to inflammasome activation. Our initial studies were performed with

PKR-deficient mice in which the N-terminal RNA binding domain of PKR was deleted [17]. In contrast, Lu et al. studied PKR using KO mice with deletion of the catalytic domain of PKR [18]. Although both KO mice lack expression of full-length PKR, some conflicting results have been reported for these two mouse mutant strains [19]. Therefore, we also studied inflammasome activation in macrophages from mutant mice with deletion of the catalytic domain of PKR. Analysis of macrophages selleck inhibitor from this Pkr−/− mouse strain also revealed comparable caspase-1 activation and pro-IL-1β/IL-18 processing in response to activators of the NLRP3 inflammasome when compared check details with that of WT macrophages (Fig. 3A). As expected, caspase-1 activation

and pro-IL-1β/IL-18 procession were abrogated in macrophages from Nlrp3−/− mice (Fig. 3A). Likewise, caspase-1 activation and pro-IL-1β maturation induced by aluminum salts (Alum), another activator of NLRP3, were unimpaired in Pkr−/− macrophages, but abolished in Nlrp3−/‒ macrophages (Fig. 3B). 2-aminopurin (2-AP), a potent inhibitor of PKR, was reported Janus kinase (JAK) to inhibit ATP-induced NLRP3 inflammasome activation at millimolar concentration [8]. Notably, addition of 2-AP at this high concentration inhibited ATP-induced NLRP3 inflammasome activation in both WT and PKR-deficient macrophages (Fig. 3C). This result suggests at this high concentration, 2-AP inhibits the inflammasome through off-target effects. Furthermore, caspase-1 activation in response to Salmonella or poly (dA:dT) were unaffected by deletion of the catalytic domain of PKR (Fig. 3D and E). Consistent with these results, IL-1β and TNF-α release induced by ATP, Salmonella and poly (dA:dT) were unimpaired in Pkr−/− macrophages (Fig. 3F and G). Our results indicate that the protein

kinase PKR plays a critical role in regulating iNOS production by macrophages after LPS challenge, which correlated with reduced intracellular killing of E. coli. However, we found no detectable role for PKR in the activation of the NLRP3, NLRC4 or AIM2 inflammasomes in macrophages. We do not have a clear explanation for the difference in results between our studies and those of Lu et al. [8]. It is possible that subtle variation in experimental conditions may account, at least in part, for the differences in results. In our studies, parallel experiments were performed using macrophages from mice deficient in NLRP3 and NLRC4 that showed requirement for these inflammasomes, but not PKR, for caspase-1 activation triggered by specific stimuli.