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Maintaining an appropriate balance between subsets of CD4(+) Th and T regulatory cells (Tregs) is critical to maintain immune homeostasis and prevent autoimmunity. Through a common requirement for TGF-beta, the development of peripherally induced Tregs is intimately linked to that of Th17 cells, with the resulting lineages depending on the presence of proinflammatory cytokines such as IL-6. Currently very little is known about the molecular signaling pathways that control the development of Tregs vs Th17 cells. Reduced activity of the PI3K pathway is required for TGF-beta-mediated induction of Foxp3 expression and the suppressive activity of Tregs. To investigate how negative regulators of the PI3K pathway impact Treg development, we investigated whether SHIP, a lipid phosphatase that regulates PI3K activity, also plays a role in the development and function of Tregs. SHIP-deficient Tregs maintained suppressive capacity in vitro and in a T cell transfer model of colitis. Surprisingly, SHIP-deficient Th cells were significantly less able to cause colitis than were wild-type Th cells due to a profound deficiency in Th17 cell differentiation, both in vitro and in vivo. The inability of SHIP-deficient T cells to develop into Th17 cells was accompanied by decreased IL-6-stimulated phosphorylation of STAT3 and an increased capacity to differentiate into Treg cells under the influence of TGF-beta and retinoic acid. These data indicate that SHIP is essential for normal Th17 cell development and that this lipid phosphatase plays a key role in the reciprocal regulation of Tregs and Th17 cells.

The relationship between airway inflammation and structural changes of airway remodeling, and their relative effects on airway function, are poorly understood. Remodeling is thought to result from chronic repetitive injury to the airway wall caused by airway inflammation; however, the mechanisms regulating remodeling changes have not been clearly defined. We examined the sequence of events in remodeling using three commonly used mouse models of allergic airways disease in which mice are exposed to nebulized ovalbumin for four consecutive days (acute), seven consecutive days (subacute), or three times a week for 6 wk (chronic). Surprisingly, we found that a very short period of exposure to ovalbumin was sufficient to elicit early changes of remodeling. Goblet cell hyperplasia and epithelial thickening were evident after just 4 d. In chronically challenged mice, these changes persisted and, in addition, subepithelial collagen deposition was significantly increased. This collagen deposition was associated with a failure to upregulate matrix metalloproteinase (MMP)-2, in conjunction with increased transforming growth factor-beta and MMP-9 expression. The relationship between inflammation, remodeling changes, and airway hyperresponsiveness (AHR) were examined. The acute and subacute models exhibited marked airway inflammation, whereas the chronic model had very modest inflammation. Conversely, airway fibrosis was only evident in the chronic model. AHR was present in all three models; however, it was significantly higher in the chronic model compared with the acute (P<0.05) and subacute (P<0.05) models. These data demonstrate that both airway inflammation and airway fibrosis may contribute to AHR, with airway fibrosis leading to the greatest increases in AHR.

Neonatal thymectomy (NTX) impairs T cell regulation and leads to organ-specific autoimmune disease in susceptible mouse strains. In the NOD mouse model of spontaneous type 1 diabetes, we observed that NTX dramatically accelerated autoimmune pancreatic beta cell destruction and diabetes. NTX had only a minor effect in NOD mice protected from diabetes by transgenic expression of the beta cell autoantigen proinsulin in APCs, inferring that accelerated diabetes after NTX is largely due to failure to regulate proinsulin-specific T cells. NTX markedly impaired the development of intraepithelial lymphocytes (IEL), the number of which was already reduced in euthymic NOD mice compared with control strains. IEL purified from euthymic NOD mice, specifically CD8alphaalpha TCRgammadelta IEL, when transferred into NTX-NOD mice, trafficked to the small intestinal epithelium and prevented diabetes. Transfer of prototypic CD4+CD25+ regulatory T cells also prevented diabetes in NTX-NOD mice; however, the induction of these cells by oral insulin in euthymic mice depended on the integrity of TCRgammadelta IEL. We conclude that TCRgammadelta IEL at the mucosal interface between self and nonself play a key role in maintaining peripheral tolerance both physiologically and during oral tolerance induction.