Enric Esplugues

Control of TH17 cells occurs in the small intestine

Interleukin (IL)-17-producing T helper cells (TH17) are a recently identified CD4+ T cell subset distinct from T helper type 1 (TH1) and T helper type 2 (TH2) cells. TH17 cells can drive antigen-specific autoimmune diseases and are considered the main population of pathogenic T cells driving experimental autoimmune encephalomyelitis (EAE), the mouse model for multiple sclerosis. The factors that are needed for the generation of TH17 cells have been well characterized. However, where and how the immune system controls TH17 cells in vivo remains unclear. Here, by using a model of tolerance induced by CD3-specific antibody, a model of sepsis and influenza A viral infection (H1N1), we show that pro-inflammatory TH17 cells can be redirected to and controlled in the small intestine. TH17-specific IL-17A secretion induced expression of the chemokine CCL20 in the small intestine, facilitating the migration of these cells specifically to the small intestine via the CCR6/CCL20 axis. Moreover, we found that TH17 cells are controlled by two different mechanisms in the small intestine: first, they are eliminated via the intestinal lumen; second, pro-inflammatory TH17 cells simultaneously acquire a regulatory phenotype with in vitro and in vivo immune-suppressive properties (rTH17). These results identify mechanisms limiting TH17 cell pathogenicity and implicate the gastrointestinal tract as a site for control of TH17 cells.

miR-33a/b contribute to the regulation of fatty acid metabolism and insulin signaling

Cellular imbalances of cholesterol and fatty acid metabolism result in pathological processes, including atherosclerosis and metabolic syndrome. Recent work from our group and others has shown that the intronic microRNAs hsa-miR-33a and hsa-miR-33b are located within the sterol regulatory element-binding protein-2 and -1 genes, respectively, and regulate cholesterol homeostasis in concert with their host genes. Here, we show that miR-33a and -b also regulate genes involved in fatty acid metabolism and insulin signaling. miR-33a and -b target key enzymes involved in the regulation of fatty acid oxidation, including carnitine O-octaniltransferase, carnitine palmitoyltransferase 1A, hydroxyacyl-CoA-dehydrogenase, Sirtuin 6 (SIRT6), and AMP kinase subunit-α. Moreover, miR-33a and -b also target the insulin receptor substrate 2, an essential component of the insulin-signaling pathway in the liver. Overexpression of miR-33a and -b reduces both fatty acid oxidation and insulin signaling in hepatic cell lines, whereas inhibition of endogenous miR-33a and -b increases these two metabolic pathways. Together, these data establish that miR-33a and -b regulate pathways controlling three of the risk factors of metabolic syndrome, namely levels of HDL, triglycerides, and insulin signaling, and suggest that inhibitors of miR-33a and -b may be useful in the treatment of this growing health concern.

Th17 Cells Express Interleukin-10 Receptor and Are Controlled by Foxp3− and Foxp3+ Regulatory CD4+ T Cells in an Interleukin-10-Dependent Manner

T helper 17 (Th17) cells are important for host defense against extracellular microorganisms. However, they are also implicated in autoimmune and chronic inflammatory diseases, and as such need to be tightly regulated. The mechanisms that directly control committed pathogenic Th17 cells in vivo remain unclear. We showed here that IL-17A-producing CD4+ T cells expressed interleukin-10 receptor α (IL-10Rα) in vivo. Importantly, T cell-specific blockade of IL-10 signaling led to a selective increase of IL-17A+IFN-γ⁻ (Th17) and IL-17A+IFN-γ+ (Th17+Th1) CD4+ T cells during intestinal inflammation in the small intestine. CD4+Foxp3⁻ IL-10-producing (Tr1) cells and CD4+Foxp3+ regulatory (Treg) cells were able to control Th17 and Th17+Th1 cells in an IL-10-dependent manner in vivo. Lastly, IL-10 treatment of mice with established colitis decreased Th17 and Th17+Th1 cell frequencies via direct signaling in T cells. Thus, IL-10 signaling directly suppresses Th17 and Th17+Th1 cells.

CD69 downregulates autoimmune reactivity through active transforming growth factor-β production in collagen-induced arthritis

CD69 is induced after activation of leukocytes at inflammatory sites, but its physiological role during inflammation remains unknown. We explored the role of CD69 in autoimmune reactivity by analyzing a model of collagen-induced arthritis (CIA) in WT and CD69-deficient mice. CD69-/- mice showed higher incidence and severity of CIA, with exacerbated T and B cell immune responses to type II collagen. Levels of TGF-beta1 and TGF-beta2, which act as protective agents in CIA, were reduced in CD69-/- mice inflammatory foci, correlating with the increase in the proinflammatory cytokines IL-1beta and RANTES. Local injection of blocking anti-TGF-beta antibodies increased CIA severity and proinflammatory cytokine mRNA levels in CD69+/+ but not in CD69-/- mice. Moreover, in vitro engagement of CD69 induced total and active TGF-beta1 production in Concanavalin A-activated splenocyte subsets, mouse and human synovial leukocytes, and Jurkat stable transfectants of human CD69 but not in the parental CD69 negative cell line. Our results show that CD69 is a negative modulator of autoimmune reactivity and inflammation through the synthesis of TGF-beta, a cytokine that in turn downregulates the production of various proinflammatory mediators.

Enhanced Antitumor Immunity in Mice Deficient in CD69

We investigated the in vivo role of CD69 by analyzing the susceptibility of CD69−/− mice to tumors. CD69−/− mice challenged with MHC class I− tumors (RMA-S and RM-1) showed greatly reduced tumor growth and prolonged survival compared with wild-type (WT) mice. The enhanced anti–tumor response was NK cell and T lymphocyte–mediated, and was due, at least in part, to an increase in local lymphocytes. Resistance of CD69−/− mice to MHC class I− tumor growth was also associated with increased production of the chemokine MCP-1, diminished TGF-β production, and decreased lymphocyte apoptosis. Moreover, the in vivo blockade of TGF-β in WT mice resulted in enhanced anti–tumor response. In addition, CD69 engagement induced NK and T cell production of TGF-β, directly linking CD69 signaling to TGF-β regulation. Furthermore, anti-CD69 antibody treatment in WT mice induced a specific down-regulation in CD69 expression that resulted in augmented anti–tumor response. These data unmask a novel role for CD69 as a negative regulator of anti–tumor responses and show the possibility of a novel approach for the therapy of tumors.

Bcl6 expression specifies the T follicular helper cell program in vivo

A novel Bcl6 reporter mouse is used to dissect the developmental requirements, plasticity, and genetic profile of Tfh cells.

Mir-33 regulates cell proliferation and cell cycle progression

Cholesterol metabolism is tightly regulated at the cellular level and is essential for cellular growth. microRNAs (miRNAs), a class of noncoding RNAs, have emerged as critical regulators of gene expression, acting predominantly at posttranscriptional level. Recent work from our group and others has shown that hsa-miR-33a and hsa-miR-33b, miRNAs located within intronic sequences of the Srebp genes, regulate cholesterol and fatty acid metabolism in concert with their host genes. Here, we show that hsa-miR-33 family members modulate the expression of genes involved in cell cycle regulation and cell proliferation. MiR-33 inhibits the expression of the cyclin-dependent kinase 6 (CDK6) and cyclin D1 (CCND1), thereby reducing cell proliferation and cell cycle progression. Overexpression of miR-33 induces a significant G1 cell cycle arrest in Huh7 and A549 cell lines. Most importantly, inhibition of miR-33 expression using 2’fluoro/methoxyethyl-modified (2’F/MOE-modified) phosphorothioate backbone antisense oligonucleotides improves liver regeneration after partial hepatectomy (PH) in mice, suggesting an important role for miR-33 in regulating hepatocyte proliferation during liver regeneration. Altogether, these results suggest that Srebp/miR-33 locus may cooperate to regulate cell proliferation, cell cycle progression and may also be relevant to human liver regeneration.

CD84 functions as a homophilic adhesion molecule and enhances IFN-gamma secretion: adhesion is mediated by Ig-like domain 1.

CD84 is a member of the CD2 subset of the Ig superfamily of cell surface molecules. Its cytoplasmic tail binds to Src homology 2 domain-containing protein 1A (signaling lymphocytic activation molecule-associated protein), a protein encoded by the X-linked lymphoproliferative disease gene. It is preferentially expressed on B lymphocytes, monocytes, and platelets. We show that it is also expressed on thymocytes and T cells. CD84 was positive on CD4−CD8− thymocytes, and its expression decreased with cell maturation. It is expressed on mature T cells preferentially on CD45RO+. To identify the CD84 ligand, we generated a soluble Ig fusion protein containing the human CD84 extracellular domains (CD84-Ig). Because receptor-ligand interactions occur between several members of this subfamily, we assayed CD84-Ig binding with all members of the CD2 family. CD84-Ig bound to CD84-transfected cells, whereas no binding was detected with cells expressing other CD2 subfamily receptors, showing that CD84 binds to itself. Anti-CD84 mAbs recognizing epitopes wholly within domain 1 of CD84 blocked the binding of the CD84-Ig fusion protein to CD84-transfected cells and platelets. Data from CD84 domain human/mouse chimeras further revealed that only the first extracellular domain of the molecule is involved in the ligand receptor recognition. The CD84-CD84 interaction was independent of its cytoplasmic tail. Finally, concurrent ligation of human CD84 with mAbs or CD84-Ig and CD3 enhanced IFN-γ secretion in human lymphocytes. Thus, CD84 is its own ligand and acts as a costimulatory molecule.

The Adaptor Protein 3BP2 Binds Human CD244 and Links this Receptor to Vav Signaling, ERK Activation, and NK Cell Killing

Adaptor proteins, molecules that mediate intermolecular interactions, are crucial for cellular activation. The adaptor 3BP2 has been shown to positively regulate NK cell-mediated cytotoxicity. In this study we present evidence for a physical interaction between 3BP2 and the CD244 receptor. CD244, a member of the CD150 family, is a cell surface protein expressed on NK, CD8+ T, and myeloid cells. CD244 interacts via its Src homology 2 domain with the X-linked lymphoproliferative disease gene product signaling lymphocytic activation molecule-associated protein (SAP)/SH2 domain protein 1A. 3BP2 interacts with human but not murine CD244. CD244-3BP2 interaction was direct and regulated by phosphorylation, as shown by a three-hybrid analysis in yeast and NK cells. Tyr337 on CD244, part of a consensus motif for SAP/SH2 domain protein 1A binding, was critical for the 3BP2 interaction. Although mutation of Tyr337 to phenylalanine abrogated human 3BP2 binding, we still observed SAP association, indicating that this motif is not essential for SAP recruitment. CD244 ligation induced 3BP2 phosphorylation and Vav-1 recruitment. Overexpression of 3BP2 led to an increase in the magnitude and duration of ERK activation, after CD244 triggering. This enhancement was concomitant with an increase in cytotoxicity due to CD244 ligation. However, no differences in IFN-γ secretion were found when normal and 3BP2-transfected cells were compared. These results indicate that CD244-3BP2 association regulates cytolytic function but not IFN-γ release, reinforcing the hypothesis that, in humans, CD244-mediated cytotoxicity and IFN-γ release involve distinct NK pathways.

CD69 limits early inflammatory diseases associated with immune response to Listeria monocytogenes infection

Mouse infection with intracellular bacteria induces a potent inflammatory response that requires protective mechanisms to avoid infection‐induced immune pathology. CD69 is expressed in all leukocytes during activation after infection with a wide range of microbial pathogens. This study explores the way in which CD69 affects cell activation after Listeria monocytogenes (Lm) infection and its effects on host protection. We show that infectivity and bacterial clearance capability are unaltered in CD69−/− peritoneal macrophages, bone marrow‐derived macrophages and dendritic cells. We found no major altered cell populations in splenocytes of Lm‐infected CD69−/− mice. However, an increase in the expression of Th1 cytokines was observed after infection, with increased production of type I and II interferon (IFN). In addition, CD69−/− splenocytes showed increased apoptosis, consistent with IFN enhancement of lymphocyte apoptosis in response to Lm infection. CD69−/− mice showed liver and spleen damage, and greatly increased susceptibility to Lm infection, compared with wild‐type controls. Lm‐specific T cells were decreased in CD69−/− mice even if T‐cell cross‐presentation and T‐cell intrinsic priming response were not compromised. As listeriosis was increased as early as day 1 post‐infection but CD69−/−RAG2−/− mice were more efficient at controlling Listeria, we propose that CD69 controls the cross‐talk between innate components and lymphocytes. These results highlight a role for CD69 in preventing infection‐induced immunopathology.