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Maintaining immune tolerance requires the production of Foxp3-expressing regulatory T (Treg) cells in the thymus. Activation of NF-κB transcription factors is critically required for Treg cell development, partly via initiating Foxp3 expression. NF-κB activation is controlled by a negative feedback regulation through the ubiquitin editing enzyme A20, which reduces proinflammatory signaling in myeloid cells and B cells. In naive CD4+ T cells, A20 prevents kinase RIPK3-dependent necroptosis. Using mice deficient for A20 in T lineage cells, we show that thymic and peripheral Treg cell compartments are quantitatively enlarged because of a cell-intrinsic developmental advantage of A20-deficient thymic Treg differentiation. A20-deficient thymic Treg cells exhibit reduced dependence on IL-2 but unchanged rates of proliferation and apoptosis. Activation of the NF-κB transcription factor RelA was enhanced, whereas nuclear translocation of c-Rel was decreased in A20-deficient thymic Treg cells. Furthermore, we found that the increase in Treg cells in T cell–specific A20-deficient mice was already observed in CD4+ single-positive CD25+ GITR+ Foxp3− thymic Treg cell progenitors. Treg cell precursors expressed high levels of the tumor necrosis factor receptor superfamily molecule GITR, whose stimulation is closely linked to thymic Treg cell development. A20-deficient Treg cells efficiently suppressed effector T cell–mediated graft-versus-host disease after allogeneic hematopoietic stem cell transplantation, suggesting normal suppressive function. Holding thymic production of natural Treg cells in check, A20 thus integrates Treg cell activity and increased effector T cell survival into an efficient CD4+ T cell response.

NKT cells represent a small subset of glycolipid-recognizing T cells that are heavily implicated in human allergic, autoimmune, and malignant diseases. In the thymus, precursor cells recognize self-glycolipids by virtue of their semi-invariant TCR, which triggers NKT cell lineage commitment and maturation. During their development, NKT cells are polarized into the NKT1, NKT2, and NKT17 subsets, defined through their cytokine-secretion patterns and the expression of key transcription factors. However, we have largely ignored how the differentiation into the NKT cell subsets is regulated. In this article, we describe the mRNA-binding Roquin-1 and -2 proteins as central regulators of murine NKT cell fate decisions. In the thymus, T cell–specific ablation of the Roquin paralogs leads to a dramatic expansion of NKT17 cells, whereas peripheral mature NKT cells are essentially absent. Roquin-1/2–deficient NKT17 cells show exaggerated lineage-specific expression of nearly all NKT17-defining proteins tested. We show through mixed bone marrow chimera experiments that NKT17 polarization is mediated through cell-intrinsic mechanisms early during NKT cell development. In contrast, the loss of peripheral NKT cells is due to cell-extrinsic factors. Surprisingly, Roquin paralog–deficient NKT cells are, in striking contrast to conventional T cells, compromised in their ability to secrete cytokines. Altogether, we show that Roquin paralogs regulate the development and function of NKT cell subsets in the thymus and periphery.

Th17 cells are a proinflammatory subset of effector T cells that have been implicated in the pathogenesis of asthma. Their production of the cytokine IL-17 is known to induce local recruitment of neutrophils, but the direct impact of IL-17 on the lung epithelium is poorly understood. In this study, we describe a novel mouse model of spontaneous IL-17–driven lung inflammation that exhibits many similarities to asthma in humans. We have found that STAT3 hyperactivity in T lymphocytes causes an expansion of Th17 cells, which home preferentially to the lungs. IL-17 secretion then leads to neutrophil infiltration and lung epithelial changes, in turn leading to a chronic inflammatory state with increased mucus production and decreased lung function. We used this model to investigate the effects of IL-17 activity on airway epithelium and identified CXCL5 and MIP-2 as important factors in neutrophil recruitment. The neutralization of IL-17 greatly reduces pulmonary neutrophilia, underscoring a key role for IL-17 in promoting chronic airway inflammation. These findings emphasize the role of IL-17 in mediating neutrophil-driven pulmonary inflammation and highlight a new mouse model that may be used for the development of novel therapies targeting Th17 cells in asthma and other chronic pulmonary diseases.

The cytokine TNF family member B cell-activating factor (BAFF; also termed BLyS) is essential for B cell generation and maintenance. Three receptors have been identified that bind to BAFF: transmembrane activator, calcium modulator, and cyclophilin ligand interactor (TACI); B cell maturation Ag (BCMA); and BAFF-R. Recently, it was shown that A/WySnJ mice, which contain a dramatically reduced peripheral B cell compartment due to decreased B cell life span, express a mutant BAFF-R. This finding, together with normal or enhanced B cell generation in mice deficient for BCMA or TACI, respectively, suggested that the interaction of BAFF with BAFF-R triggers signals essential for the generation and maintenance of mature B cells. However, B cells in mice deficient for BAFF differ phenotypically and functionally from A/WySnJ B cells. Residual signaling through the mutant BAFF-R could account for these differences. Alternatively, dominant-negative interference by the mutant receptor could lead to an overestimation of the importance of BAFF-R. To resolve this issue, we generated BAFF-R-null mice. Baff-r−/− mice display strongly reduced late transitional and follicular B cell numbers and are essentially devoid of marginal zone B cells. Overexpression of Bcl-2 rescues mature B cell development in Baff-r−/− mice, suggesting that BAFF-R mediates a survival signal. CD21 and CD23 surface expression are reduced on mature Baff-r−/− B cells, but not to the same extent as on mature B cells in BAFF-deficient mice. In addition, we found that Baff-r−/− mice mount significant, but reduced, Ag-specific Ab responses and are able to form spontaneous germinal centers in mesenteric lymph nodes. The reduction in Ab titers correlates with the reduced B cell numbers in the mutant mice.

Signal transduction from proinflammatory stimuli leading to NF-κB-dependent gene expression is mediated by the IκB kinase 2 (IKK2/IKKβ). Therefore, IKK2 has become an important drug target for treatment of inflammatory conditions. T cells, whose activation depends to a large extent on the activity of NF-κB transcription factors, play important roles in inflammation and autoimmunity. Ablation of IKK2 specifically in T cells in CD4cre/Ikk2FL mice allows their survival and activation by polyclonal stimuli in vitro, suggesting that IKK2 is dispensable for T cell activation. We report in this study that IKK2-deficient T cells expand efficiently in response to superantigen administration in vivo, but are completely deficient in recall responses, most likely due to inefficient priming. IKK2-deficient T cells provide suboptimal B cell help and fail to support germinal center reactions. Finally, IKK2 is essential for homeostatic expansion of naive T cells, reflected by the inability of IKK2-deficient T cells to induce colitis in lymphopenic hosts.

Fogli, L. K., M. S. Sundrud, S. Goel, S. Bajwa, K. Jensen, E. Derudder, A. Sun, M. Coffre, C. Uyttenhove, J. Van Snick, M. Schmidt-Supprian, A. Rao, G. Grunig, J. Durbin, S. S. Casola, K. Rajewsky, and S. B. Koralov. 2013. T cell–derived IL-17 mediates epithelial changes in the airway and drives