C57BL/6 (WT) and IL-6 KO mice were purchased from The Jackson Laboratory. RAG2/IL2rg DKO mice were purchased from Taconic Farms. IL-21R–deficient mice (Ozaki et al., 2002 (link)), IL-23R-GFP reporter mice (Awasthi et al., 2009 (link)), STAT-3–deficient mice (Lee et al., 2002 (link)), and IL-17A/F–deficient mice (Ogura et al., 2008 (link); Ishigame et al., 2009 (link)) were generated and provided by the referenced collaborators. Crosses of these various strains were generated and maintained in the animal facilities of the National Institutes of Health (NIH) in Bethesda or Frederick, MD, in full compliance with institutional guidelines. Male and female mice aged 6 to 12 wk were used for analyses. Littermate controls were used for all experiments with STAT-3 KO mice. TKO mice were derived from the respective single KO mice and bred homozygously. Their controls were in-house WT mice. All studies were performed under specific pathogen–free (SPF) conditions in compliance with NIH institutional guidelines, under IACUC-approved protocols (NEI-581 and NIAID/LCID 8E).