CD4 T cells are tightly regulated by microbiota in the intestine, but whether intestinal T cells interface with host-derived metabolites is less clear. Here, we show that CD4 T effector (Teff) cells upregulated the xenobiotic transporter, Mdr1, in the ileum to maintain homeostasis in the presence of bile acids. Whereas wild-type Teff cells upregulated Mdr1 in the ileum, those lacking Mdr1 displayed mucosal dysfunction and induced Crohn's disease-like ileitis following transfer into Rag1 hosts. Mdr1 mitigated oxidative stress and enforced homeostasis in Teff cells exposed to conjugated bile acids (CBAs), a class of liver-derived emulsifying agents that actively circulate through the ileal mucosa. Blocking ileal CBA reabsorption in transferred Rag1 mice restored Mdr1-deficient Teff cell homeostasis and attenuated ileitis. Further, a subset of ileal Crohn's disease patients displayed MDR1 loss of function. Together, these results suggest that coordinated interaction between mucosal Teff cells and CBAs in the ileum regulate intestinal immune homeostasis.

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. Here 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 utilized 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.

Cutaneous T-cell lymphoma is a heterogeneous group of lymphomas characterized by the accumulation of malignant T cells in the skin. The molecular and cellular etiology of this malignancy remains enigmatic, and what role antigenic stimulation plays in the initiation and/or progression of the disease remains to be elucidated. Deep sequencing of the tumor genome showed a highly heterogeneous landscape of genetic perturbations, and transcriptome analysis of transformed T cells further highlighted the heterogeneity of this disease. Nonetheless, using data harvested from high-throughput transcriptional profiling allowed us to develop a reliable signature of this malignancy. Focusing on a key cytokine signaling pathway previously implicated in cutaneous T-cell lymphoma pathogenesis, JAK/STAT signaling, we used conditional gene targeting to develop a fully penetrant small animal model of this disease that recapitulates many key features of mycosis fungoides, a common variant of cutaneous T-cell lymphoma. Using this mouse model, we show that T-cell receptor engagement is critical for malignant transformation of the T lymphocytes and that progression of the disease is dependent on microbiota.

Antibody repertoires are known to be shaped by selection for antigen binding. Unexpectedly, we now show that selection also acts on a non-antigen-binding antibody region: the heavy-chain variable (V H )-encoded "elbow" between variable and constant domains. By sequencing 2.8 million recombined heavy-chain genes from immature and mature B-cell subsets in mice, we demonstrate a striking gradient in V H gene use as pre-B cells mature into follicular and then into marginal zone B cells. Cells whose antibodies use V H genes that encode a more flexible elbow are more likely to mature. This effect is distinct from, and exceeds in magnitude, previously described maturation-associated changes in heavy-chain complementarity determining region 3, a key antigen-binding region, which arise from junctional diversity rather than differential V H gene use. Thus, deep sequencing reveals a previously unidentified mode of B-cell selection.immunomics | principal component analysis | development T he mature antibody repertoire is shaped by selective forces that influence B-cell survival (1). Comparison of immature and mature B-cell subsets has shown that selection acts specifically on complementarity determining region 3 (CDR3) of the antibody heavy-chain molecule, an antigen-binding region that is a key determinant of antigen specificity (2). On average, mature B-cell subsets express antibodies that have shorter and more negatively charged CDR3s, which is the result of selection against autoreactive and polyreactive B cells (3,4).Each recombined antibody heavy-chain gene is composed of a variable (V H ), diversity (D), and joining (J H ) gene segment. Because the CDR3 region spans the V H -D-J H joint, investigators have asked whether selection might favor B cells whose antibodies use specific V H , D, or J H gene segments. Selection in favor of specific gene segments during B-cell maturation might help to explain the observed maturation-associated changes in CDR3 length and charge, and might suggest a preference for "hard-wired" antigen specificities. Evidence against selection would suggest that differences in CDR3 result exclusively from the nontemplated addition and deletion of nucleotides at the V H -D and D-J H junctions, and therefore that the death of B cells with counterselected CDR3s during maturation is simply the evolutionary cost (3) of maintaining this mechanism of generating antibody diversity.Nearly two decades ago, a low-throughput sequencing study in mice suggested that specific V H gene segments were used at different frequencies by pre-B cells (in which heavy-chain recombination has been completed) and mature B cells in the spleen (5). This observation was interpreted as selection for hard-wired specificities. However, the statistical robustness of this observation was limited by the small number of recombined genes that were sequenced, and although subsequent investigations have detected differences in V H use between pre-B and upstream pro-B cells, they have failed to confirm such differences between pre-B and...