This is not what we observed. In contrast, the absence of the proximal promoter did not decrease circulating sST2 concentrations, either in naïve or allergen-challenged mice. Although the cellular source of sST2 in the blood is still not known, these findings suggest fibroblasts are not a major source under the conditions tested. It remains possible, however, that fibroblasts and/or the proximal promoter and enhancer are important for sST2 induction in

other physiological settings; this is something future studies with these mice may help reveal. In the course of these experiments we also found that fibroblasts use the proximal promoter to express ST2L and are functionally responsive to IL-33, as demonstrated by the AZD3965 ic50 gene induction of the neutrophil-attracting CXCL1 and other chemokines. Examination of these mice in models of fibrosis could therefore be informative due to the central role of fibroblasts and recent evidence implicating IL-33 in fibrotic disease [21]. Finally, we hypothesize that there are other nonimmune cell types that require the proximal promoter for ST2L expression and that these mice may thus be useful for examining tissue-specific IL-33 responses in vivo. A targeting vector was

constructed to delete a region in the ST2 locus beginning 4490 bp upstream of the +1 initiation site (ACGTGGGT) in exon 1b and ending at the 3′ end of exon 1b (83 bp downstream from the +1 site), as illustrated in Fig. 1A. The Inhibitor Library targeting construct was electroporated into 129×C57Bl/6 F1 hybrid ES cells and clones were then transfected with a CRE recombinase-expressing plasmid to delete the Neo cassette prior to injecting for germline transmission in C57Bl/6 mice using standard conditions. For splenocytes, spleens were minced

and single cell suspensions were collected through a nylon mesh. RBCs were lysed and cells were cultured for 3 h in RPMI with 10% FBS prior to RNA isolation. For mast cells, bone marrow cells were cultured in Iscove’s Modified Dulbecco’s Medium supplemented with 10% FBS, IL-3 (5 ng/mL, Amgen), and SCF (100 ng/mL, Silibinin Amgen) at approximately 2–5 × 105 cells/mL. Every 3–4 days nonadherent cells were transferred to new flasks. Flow cytometry was performed after 5 weeks using antibodies to ST2 (MD Bioproducts, clone DJ8) and c-kit (CD117, BD Pharmingen, clone 2B8). BMMCs were cultured overnight at 105 cells/well with or without IL-33 (Amgen) and IL-6 was measured in the supernatant by ELISA (R&D Systems). For fibroblasts, deboned tails from 12-week-old euthanized mice were minced in HBSS followed by digestion in a 1:1 solution of collagenase (Type XI-S Sigma in HBSS; 2000 U/mL) at 37°C for 30 min, and then 0.05% trypsin at 37°C for 20 min, followed by quenching (DMEM + 15% heat-inactivated calf serum). Cells were cultured in 10 cm plates for 5–7 days.