Jak2 Modulates Innate Immunity Figure 2. Jak2 deficiency selectively attenuates the capacity of DCs to initiate innate immune response. (A) Loss of Jak2 attenuates the capacity of DCs secretion of proinflammatory cytokines. Supernatants of BMDCs with or without LPS stimulation were harvested and subjected to ELISA analysis of cytokine secretion. BMDCs deficient for Jak2 showed significant reduced capacity to secrete TNFa and IL-12. (B) Jak2 failed to show perceptible impact on macrophages secretion of proinflammatory cytokines. PEM derived from Jak22/2 and control mice were cultured with or without LPS stimulation and supernatants were harvested for ELISA analysis as above, respectively. (C) Jak22/2 mice showed impaired early clearance of Listeria. Jak22/2 and control mice were i.v. injected with ,1 LD50 Listeria Monocytogenes in PBS. Spleens and livers were harvested after 48 h infection. Serial 10-fold dilutions of organ homogenates were plated on TSB-agar and CFU were counted after 48 h incubation. Left panel: a representative results for cultures inoculated with homogenates; right panel: a bar graphic figure showing the average CFU/organ of 3 independent experiments. All data are present as mean 6 SE. *, p,0.05; **, p,0.01; ***, p,0.001. doi:10.1371/journal.pone.0009593.g002 Jak22/2 BMDCs or splenic DCs were first pulsed with 1 mM OVA peptide, and then cocultured with OT-1 T cells as above. Similarly, both Jak22/2 BMDCs and splenic DCs were potent to stimulate antigen-specific T cell activation (Figure 3B). Next, we analyzed cytokine profile of T cells activated by Jak22/2 DCs. We selectively analyzed the production of IFN-c (Th1), IL-10 (Th2) and IL-17 (Th17) by ELISA analysis of above collected culture supernatants. Once again, Jak22/2 DCs were as potent as control DCs to stimulate T cells secretion of IFN-c, IL- 10, and IL-17 (Figure 3C). Taken together, these results indicate that loss of Jak2 only selectively inhibits the potency of DCs to initiate innate immune response without perceptible effect on DC- mediated adaptive immune response. Jak22/2 Mice Are Remarkably Resistant to Lethal Dose of LPS-Induced Septic Shock Given the role that Jak2 selectively regulates DC-mediated innate immune response, we next examined its implication in the pathogenesis of septic shock, in which excessive innate immune response is suggested to be responsible for the disease etiology [32– 34]. To this end, 8 wk-old male Cre+/+Jak2fl/fl mice were first induced with tamoxifen or control vehicle as above. Four weeks later, lethal dose of LPS (50 mg/kg body weight) was then administered into each mouse via i.p. injection. In general, all control mice were much weaker as compared with that of Jak22/2 mice after 6–12 h of injection, and remarkably, 14 out of 18 control mice (78%) died within 36 h of injection. In sharp contrast, 17 out of 20 Jak22/2 mice have completely recovered from lethal dose of LPS challenge (Figure 4A, 85% vs. 22%, p,0.0001), indicating that loss of Jak2 protected mice from lethal dose of LPS-induced septic death. To confirm that the protective effect observed in Jak22/2 mice was DC-dependent, we next performed an adoptive transfer study using DCs originated from wild-type mice. To this end, the irradiated Jak22/2 mice and their corresponding controls were adoptively transferred 16107 normal BMDCs followed by challenging with lethal dose of LPS as described. As expected, both Jak22/2 and control mice PLoS ONE | www.plosone.org 4 March 2010 | Volume 5 | Issue 3 | e9593