Jak2 Modulates Innate Immunity Figure 1. Jak2 is essential for DC development and maturation. (A) Tamoxifen efficiently induced Jak2 deficiency in DCs. BMDCs were generated from Cre+/+Jak2fl/fl mice after 2 wk of tamoxifen or carrier solution induction and then subjected to Western blot analysis of Jak2 expression. High levels of Jak2 were detected in control mice, while Jak2 was absent in tamoxifen induced mice. (B) Loss of Jak2 significantly reduced BMDC yield. Bone marrow cells (16107) were used to generate BMDCs using GM-CSF (10 ng/ml) and IL-4 (5 ng/ml) as described. Bone marrow cells deficient for Jak2 showed 1.3-fold decrease of BMDC yield. (C) Jak22/2 mice show significant smaller spleen size. Top panel: a bar graphic figure showing the average spleen weight of all mice analyzed; bottom panel: representative spleens from Jak22/2 and control mice. (D) Analysis of splenocytes in Jak22/2 and control mice. Both total splenocytes and the percentage of splenic DCs in total splenocytes were reduced in Jak22/2 mice as compared with that of controls. (E) BMDC surface marker expressions in the unstimulated condition. Left panel: a representative of flow cytometry data; right panel: a bar graphic figure showing the average percentage of BMDCs positive for each surface marker analyzed. (F) BMDC surface marker expressions after LPS stimulation. Similar as above, left panel is a representative of flow cytometry data, and right panel shows the average percentage of BMDCs positive for the corresponding surface marker. All data are present as mean 6 SE of four replicates. *, p,0.05; **, p,0.01; ***, p,0.001. doi:10.1371/journal.pone.0009593.g001 Jak22/2 BMDCs showed similar potency as control BMDCs to stimulate alloreactive BALB/c T cell proliferation (Figure 3A, left panel). To confirm this observation, we performed similar studies using splenic DCs. Splenocytes pooled from 5 Jak22/2 or control mice were used to enrich splenic DCs as described. Irradiated splenic DCs (2000 rads) were then cocultured with BALB/c T cells as above, respectively. Consistently, splenic Jak22/2 DCs were potent to stimulate alloreactive T cell activation (Figure 3A, right panel). We next examined the capacity of Jak22/2 DCs to initiate antigen-specific T cell activation. For this purpose, irradiated PLoS ONE | www.plosone.org 3 March 2010 | Volume 5 | Issue 3 | e9593