Human neutrophil adherence to ECMs induces an initial inhibition of stimulated reactive oxygen species (ROS) formation, followed by an enhanced phase of oxidant production. The initial integrin-mediated suppression of ROS constitutes a mechanism to prevent inappropriate tissue damage as leukocytes migrate to inflammatory sites. The Rac2 guanosine 5′-triphosphatase (GTPase) is a critical regulatory component of the phagocyte NADPH oxidase. We show that activation of Rac2 is inhibited in adherent neutrophils, correlating with inhibition of ROS formation. Conversely, NADPH oxidase components p47 and p67 assemble normally, suggesting a specific action of adhesion on the Rac2 molecular switch. Reconstitution with activated Rac2 restored rapid NADPH oxidase activation kinetics to adherent neutrophils, establishing that inhibition was due to defective Rac2 activity. We provide evidence that integrins inhibit Rac2 activation via a membrane-associated guanine nucleotide exchange factor, likely to be Vav1. Activation of Vav1, but not its upstream activator, Syk, is suppressed by cell adhesion. Vav1 activity is inhibited due to dephosphorylation of the regulatory Tyr174 via enhanced tyrosine phosphatase activity in adherent cells. These studies identify an integrin-mediated pathway in which Vav1 is as a strong candidate for the critical regulatory point in suppression of Rac2 activation and ROS generation during inflammatory responses.
Tieming Zhao, Valerie Benard, Benjamin P. Bohl, Gary M. Bokoch
Notch signaling plays a fundamental role in determining the outcome of differentiation processes in many tissues. Notch signaling has been implicated in T versus B cell lineage commitment, thymic differentiation, and bone marrow hematopoietic precursor renewal and differentiation. Notch receptors and their ligands are also expressed on the surface of mature lymphocytes and APCs, but the effects of Notch signaling in the peripheral immune system remain poorly defined. The aim of the studies reported here was to investigate the effects of signaling through the Notch receptor using a ligand of the Delta-like family. We show that Notch ligation in the mature immune system markedly decreases responses to transplantation antigens. Constitutive expression of Delta-like 1 on alloantigen-bearing cells renders them nonimmunogenic and able to induce specific unresponsiveness to a challenge with the same alloantigen, even in the form of a cardiac allograft. These effects could be reversed by depletion of CD8+ cells at the time of transplantation. Ligation of Notch on splenic CD8+ cells results in a dramatic decrease in IFN-γ with a concomitant enhancement of IL-10 production, suggesting that Notch signaling can alter the differentiation potential of CD8+ cells. These data implicate Notch signaling in regulation of peripheral immunity and suggest a novel approach for manipulating deleterious immune responses.
Kenneth K. Wong, Matthew J. Carpenter, Lesley L. Young, Susan J. Walker, Grahame McKenzie, Alyson J. Rust, George Ward, Laura Packwood, Karen Wahl, Luc Delriviere, Gerard Hoyne, Paul Gibbs, Brian R. Champion, Jonathan R. Lamb, Margaret J. Dallman
CC chemokine ligand 21 (CCL21)/secondary lymphoid chemokine (SLC), a ligand for CC chemokine receptor 7 (CCR7), has been demonstrated to play a vital role in the homing and localization of immune cells to lymphoid tissues, but its role in nonlymphoid tissues largely remains undefined. Here, we provide evidence that CCL21 in lymphoid and nonlymphoid tissues is differentially regulated by lymphotoxin-dependent (LT-dependent) and -independent mechanisms, respectively. This differential regulation is due to the selective regulation of the CCL21-Ser/CCL21a but not the CCL21-Leu/CCL21b gene by the LT and noncanonical NF-κB pathways. This alternate pathway, not dependent on LT or lymphocytes, leading to constitutive expression of CCL21 in nonlymphoid tissues, is critical for the initial recruitment of T lymphocytes to peripheral effector sites. CCL21 expression is subsequently further enhanced in a LT-dependent fashion following airway challenge, potentially facilitating a positive feedback loop to attract additional CCR7+ effector cells. These findings establish an essential role for CCL21 in the recruitment of effector T cells to peripheral tissues and suggest that LT-dependent and -independent regulation of CCL21 plays a role in balancing the central and peripheral immune responses between lymphoid and nonlymphoid tissues.
James C. Lo, Robert K. Chin, Youjin Lee, Hyung-Sik Kang, Yang Wang, Joel V. Weinstock, Theresa Banks, Carl F. Ware, Guido Franzoso, Yang-Xin Fu
CD4+ helper T cells play a critical role in the production of the antinuclear autoantibodies that characterize systemic lupus erythematosus in mice and humans. A key issue is whether this help is derived from a diverse repertoire of autoreactive CD4+ T cells or from a select number of T cells of limited specificity. We used the chronic graft-versus-host disease model to define the diversity of the CD4+ T cell repertoire required to induce the autoantibody response. By transferring clonally restricted versus clonally diverse populations of MHC class II–reactive CD4+ T cells, we show that the loss of B cell tolerance to nuclear antigens has two distinct components with different CD4+ cell requirements. Activation of limited repertoires of CD4+ T cells was sufficient for the expansion of anergized anti–double-stranded DNA B cells and production of IgM autoantibodies. Unexpectedly, we found that CD4+ T cell diversity was necessary for CD4+ T cell trafficking into the follicle and for the generation of isotype-switched IgG autoantibodies. Importantly, combining two limited repertoires of T cells provides sufficient CD4+ T cell diversity to drive antinuclear Ab production. These data demonstrate that a diverse CD4+ T cell repertoire is required to generate a sustained effector B cell response capable of mediating systemic autoimmunity.
Brian W. Busser, Brigette S. Adair, Jan Erikson, Terri M. Laufer
CD4+CD25+ regulatory T (TR) cells have been described in both humans and mice. In mice, TR are thymically derived, and lack of TR leads to organ-specific autoimmunity. Recently, the forkhead/winged helix transcription factor, FoxP3, has been shown to be important for the function of TR cells in mice. In this study, human TR cells were examined and, in results similar to those of studies done in mice, expression of FoxP3 was found exclusively in CD4+CD25+ T cells and correlated with the suppressive activity of these cells. In contrast to the mouse studies, activation of human CD4+CD25– T cells led to expression of FoxP3. Expression of FoxP3 in activated human CD4+CD25+ cells also correlated with suppression of proliferation by these cells in freshly isolated CD4+CD25– T cells from the same donor. This suppression was cell-contact dependent and cytokine independent. Thus, in humans, during activation of CD4+CD25– T cells in an immune response, two populations of cells may arise, effector CD4+CD25+ and regulatory CD4+CD25+ T cells, with expression of FoxP3 correlated with regulatory activity. These data also raise the possibility that a failure to generate peripheral TR cells properly may contribute to autoimmune disease and suggest a possible therapeutic role for FoxP3 in the treatment of such diseases.
Mindi R.Walker, Deborah J. Kasprowicz, Vivian H. Gersuk, Angéle Bènard, Megan Van Landeghen, Jane H. Buckner, Steven F. Ziegler
X-linked anhidrotic ectodermal dysplasia with immunodeficiency (XL-EDA-ID) is caused by hypomorphic mutations in the gene encoding NEMO/IKKγ, the regulatory subunit of the IκB kinase (IKK) complex. IKK normally phosphorylates the IκB-inhibitors of NF-κB at specific serine residues, thereby promoting their ubiquitination and degradation by the proteasome. This allows NF-κB complexes to translocate into the nucleus where they activate their target genes. Here, we describe an autosomal-dominant (AD) form of EDA-ID associated with a heterozygous missense mutation at serine 32 of IκBα. This mutation is gain-of-function, as it enhances the inhibitory capacity of IκBα by preventing its phosphorylation and degradation, and results in impaired NF-κB activation. The developmental, immunologic, and infectious phenotypes associated with hypomorphic NEMO and hypermorphic IKBA mutations largely overlap and include EDA, impaired cellular responses to ligands of TIR (TLR-ligands, IL-1β, and IL-18), and TNFR (TNF-α, LTα1/β2, and CD154) superfamily members and severe bacterial diseases. However, AD-EDA-ID but not XL-EDA-ID is associated with a severe and unique T cell immunodeficiency. Despite a marked blood lymphocytosis, there are no detectable memory T cells in vivo, and naive T cells do not respond to CD3-TCR activation in vitro. Our report highlights both the diversity of genotypes associated with EDA-ID and the diversity of immunologic phenotypes associated with mutations in different components of the NF-κB signaling pathway.
Gilles Courtois, Asma Smahi, Janine Reichenbach, Rainer Döffinger, Caterina Cancrini, Marion Bonnet, Anne Puel, Christine Chable-Bessia, Shoji Yamaoka, Jacqueline Feinberg, Sophie Dupuis-Girod, Christine Bodemer, Susanna Livadiotti, Francesco Novelli, Paolo Rossi, Alain Fischer, Alain Israël, Arnold Munnich, Françoise Le Deist, Jean-Laurent Casanova
Containment of hepatitis C virus (HCV) and other chronic human viral infections is associated with persistence of virus-specific CD4 T cells, but ex vivo characterization of circulating CD4 T cells has not been achieved. To further define the phenotype and function of these cells, we developed a novel approach for the generation of tetrameric forms of MHC class II/peptide complexes that is based on the cellular peptide-exchange mechanism. HLA-DR molecules were expressed as precursors with a covalently linked CLIP peptide, which could be efficiently exchanged with viral peptides following linker cleavage. In subjects who spontaneously resolved HCV viremia, but not in those with chronic progressive infection, HCV tetramer–labeled cells could be isolated by magnetic bead capture despite very low frequencies (1:1,200 to 1:111,000) among circulating CD4 T cells. These T cells expressed a set of surface receptors (CCR7+CD45RA–CD27+) indicative of a surveillance function for secondary lymphoid structures and had undergone significant in vivo selection since they utilized a restricted Vβ repertoire. These studies demonstrate a relationship between clinical outcome and the presence of circulating CD4 T cells directed against this virus. Moreover, they show that rare populations of memory CD4 T cells can be studied ex vivo in human diseases.
Cheryl L. Day, Nilufer P. Seth, Michaela Lucas, Heiner Appel, Laurent Gauthier, Georg M. Lauer, Gregory K. Robbins, Zbigniew M. Szczepiorkowski, Deborah R. Casson, Raymond T. Chung, Shannon Bell, Gillian Harcourt, Bruce D. Walker, Paul Klenerman, Kai W. Wucherpfennig
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-β1 and TGF-β2, which act as protective agents in CIA, were reduced in CD69–/– mice inflammatory foci, correlating with the increase in the proinflammatory cytokines IL-1β and RANTES. Local injection of blocking anti–TGF-β 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-β1 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-β, a cytokine that in turn downregulates the production of various proinflammatory mediators.
David Sancho, Manuel Gómez, Fernando Viedma, Enric Esplugues, Mónica Gordón-Alonso, María Angeles García-López, Hortensia de la Fuente, Carlos Martínez-A, Pilar Lauzurica, Francisco Sánchez-Madrid
IL-12 p40–related cytokines such as IL-12 p35/p40 heterodimer and IL-23 (p19/p40) are potent regulators of adaptive immune responses. Little is known, however, about the transcriptional regulation of the p40 gene in vivo. In an attempt toward this goal, we have generated transgenic mice expressing firefly luciferase under the control of the IL-12 p40 promoter. High constitutive transgene expression was found in the small intestine only, whereas little reporter gene activity was observed in other tissues. Within the small bowel, constitutive promoter activity was restricted to the terminal ileum and associated with high expression of p40 mRNA as well as p40 and IL-23 p19/p40 proteins. The cells constitutively producing IL-12 p40 were identified as CD8α and CD11b double-negative CD11c+ lamina propria dendritic cells (LPDCs) that represent a major cell population in the lamina propria of the small intestine, but not in the colon. FISH directly demonstrated the uptake of bacteria by a subset of LPDCs in the terminal ileum that was associated with p40 expression. Furthermore, little or no p40 protein expression in LPDCs was found in the terminal ileum of germfree mice, indicating a key role of the intestinal flora for constitutive p40 expression. In addition, analysis of transgenic mice with a mutated NF-κB target site in the p40 promoter showed a critical role of NF-κB for constitutive transgene expression. Our data reveal important functional differences between the mucosal immune systems of the small and large bowel in healthy mice and suggest that the high bacterial load in the terminal ileum activates p40 gene transcription in LPDCs through NF-κB. These data suggest a predisposition of the terminal ileum to develop chronic inflammatory responses through IL-23 and thus may provide a molecular explanation for the preferential clinical manifestation of Crohn disease in this part of the gut.
Christoph Becker, Stefan Wirtz, Manfred Blessing, Jaana Pirhonen, Dennis Strand, Oliver Bechthold, Julia Frick, Peter R. Galle, Ingo Autenrieth, Markus F. Neurath
CD1d is expressed on the surface of professional and nonprofessional APCs, including intestinal epithelial cells (IECs), for a role in the presentation of glycolipid-based antigens to subsets of T cells. The mechanisms that regulate CD1d expression in any cell type are unknown. To investigate the possibility that expression of CD1d is influenced by exogenous factors present within the intestinal lumen, CD1d expression was analyzed in several IEC lines after culturing in the presence of lumenal contents (LC) of the normal human intestine. Exposure of the colon-derived cell lines T84, HT-29, and Caco-2 to soluble LC resulted in a marked induction of CD1d expression as determined by RT-PCR, confocal microscopy, cell surface ELISA, and Western blot analysis. Similarly, exposure of human IECs to LC isolated from mice bred in both specific pathogen–free and germfree conditions also resulted in the induction of CD1d expression, with the maximum CD1d-inducing activity observed in the small intestine. Biochemical and biophysical characterization of the human CD1d-inducing activity identified heat shock protein 110 (Hsp110) as a major functional component of the LC that contributes to CD1d surface regulation, and immunolocalization studies revealed Hsp110 expression in subsets of human IECs in vivo. These data support the presence of a novel autocrine pathway of CD1d regulation by Hsp110.
Sean P. Colgan, Richard S. Pitman, Takashi Nagaishi, Atsushi Mizoguchi, Emiko Mizoguchi, Lloyd F. Mayer, Ling Shao, R. Balfour Sartor, John R. Subjeck, Richard S. Blumberg