Amy Sun

T cell-derived IL-17 mediates epithelial changes in the airway and drives pulmonary neutrophilia.

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.

Antibody repertoire deep sequencing reveals antigen-independent selection in maturing B cells

Significance Antibodies play essential roles in vaccination, infection, autoimmunity, aging, and cancer. A key question is how the antibody repertoire achieves its remarkable diversity. Part of the answer is that B cells, which express antibodies on their surface, are selected for survival based on the specific antigens that their antibodies bind, with antigen specificity determined by the protein sequence of antibodies’ antigen-binding regions. Unexpectedly, we find that B cells are also selected based on whether their antibodies have a loose or tight “elbow joint,” independent of the sequence of their antigen-binding regions. This discovery, enabled by sequencing technology and mathematics, adds a surprising new dimension to our understanding of antibody repertoires, and might one day help us shape them ourselves. 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 (VH)–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 VH gene use as pre-B cells mature into follicular and then into marginal zone B cells. Cells whose antibodies use VH 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 VH gene use. Thus, deep sequencing reveals a previously unidentified mode of B-cell selection.

VH replacement in primary immunoglobulin repertoire diversification

Significance The recombinatorial process of V(D)J rearrangement generates a vast antibody repertoire from a limited number of genes. The joints generated in the course of V(D)J recombination are imprecise thus yielding greater diversity but also resulting in frequent generation of nonproductive VDJ rearrangements. We have previously shown that B cells with two nonproductive IgH rearrangements can be efficiently rescued by a form of secondary V(D)J recombination called VH replacement. We now demonstrate that VH replacement also contributes to the diversity of the immune repertoire by modifying productive IgH rearrangements. Results presented herein suggest that VH replacement occurs exclusively during early stages of B-cell development and therefore does not contribute to the editing of self-reactive antibodies. The genes encoding the variable (V) region of the B-cell antigen receptor (BCR) are assembled from V, D (diversity), and J (joining) elements through a RAG-mediated recombination process that relies on the recognition of recombination signal sequences (RSSs) flanking the individual elements. Secondary V(D)J rearrangement modifies the original Ig rearrangement if a nonproductive original joint is formed, as a response to inappropriate signaling from a self-reactive BCR, or as part of a stochastic mechanism to further diversify the Ig repertoire. VH replacement represents a RAG-mediated secondary rearrangement in which an upstream VH element recombines with a rearranged VHDHJH joint to generate a new BCR specificity. The rearrangement occurs between the cryptic RSS of the original VH element and the conventional RSS of the invading VH gene, leaving behind a footprint of up to five base pairs (bps) of the original VH gene that is often further obscured by exonuclease activity and N-nucleotide addition. We have previously demonstrated that VH replacement can efficiently rescue the development of B cells that have acquired two nonproductive heavy chain (IgH) rearrangements. Here we describe a novel knock-in mouse model in which the prerearranged IgH locus resembles an endogenously rearranged productive VHDHJH allele. Using this mouse model, we characterized the role of VH replacement in the diversification of the primary Ig repertoire through the modification of productive VHDHJH rearrangements. Our results indicate that VH replacement occurs before Ig light chain rearrangement and thus is not involved in the editing of self-reactive antibodies.

The Xenobiotic Transporter Mdr1 Enforces T Cell Homeostasis in the Presence of Intestinal Bile Acids

Summary 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. Graphical Abstract Figure. No caption available. HighlightsCD4+ effector T cells upregulate Mdr1 expression in the ileumMdr1 protects effector T cells in the ileum from bile‐acid‐driven oxidative stressBile acid sequestration restores Mdr1‐deficient T cell homeostasis in the ileumA subset of ileal Crohn’s disease patients display MDR1 loss of function &NA; The role of host‐derived intestinal metabolites in mucosal immune regulation is poorly understood. Here, Cao et al. show that effector CD4+ T cells upregulate expression of the xenobiotic transporter, Mdr1, in the ileum to safeguard immune homeostasis, revealing an important immunologic consequence of ileal bile acid reabsorption.

Role of Dysregulated Cytokine Signaling and Bacterial Triggers in the Pathogenesis of Cutaneous T-Cell Lymphoma

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.