Lectin pathway activation of C3 is known to involve target recognition by mannan-binding lectin (MBL) or ficolins and generation of classical pathway C3 convertase via cleavage of C4 and C2 by MBL-associated serine protease 2 (MASP-2). We investigated C3 activation in C2-deficient human sera and in sera with other defined defects of complement to assess other mechanisms through which MBL might recruit complement. The capacity of serum to support C3 deposition was examined by ELISA using microtiter plates coated with O antigen–specific oligosaccharides derived from Salmonella typhimurium, S. thompson, and S. enteritidis corresponding to serogroups B, C, and D (BO, CO, and DO). MBL bound to CO, but not to BO and DO, and efficiently supported C3 deposition in the absence of C2, C4, or MASP-2. The existence of an MBL-dependent C2 bypass mechanism for alternative pathway–mediated C3 activation was clearly demonstrated using CO, solid-phase mannan, and E. coli LPS. MASP-1 might contribute, but was not required for C3 deposition in the model used. Independent of MBL, specific antibodies to CO supported C3 deposition through classical and alternative pathways. MBL-dependent C2 bypass activation could be particularly important in various inherited and acquired complement deficiency states.
Barbro Selander, Ulla Mårtensson, Andrej Weintraub, Eva Holmström, Misao Matsushita, Steffen Thiel, Jens C. Jensenius, Lennart Truedsson, Anders G. Sjöholm
When exposed to a pathogen, a naive CD4+ T cell is forced to make a cell fate decision that leads to a polarized population of Th1 IFN-γ– or Th2 IL-4– producing cells. Although IL-4 has traditionally been considered a factor that promotes Th2 cell differentiation, recent evidence has demonstrated that the site and timing of IL-4 expression in an immune response determines its ultimate effects on CD4+ T cell fate. Using a mast cell (MC) reconstitution model, we demonstrate that MC-derived IL-4 promoted Th1 responses in vivo. Furthermore, MCs from genetically disparate mouse strains varied in their potential for IL-4 expression. Independent of the activation mode, MCs from Th1-prone C57BL/6 mice exhibited a more robust Il4 response than did the Th2-prone strain Balb/c. The hierarchy of IL-4 expression potential was directly associated with the degree of basal chromatin accessibility at cis-regulatory elements conserved noncoding sequence–1 and VA enhancer within the Th2 locus. GATA1/2 and Ikaros, factors with opposing roles in chromatin remodeling, acted at these sites. We propose that GATA and Ikaros proteins coordinately fine-tune accessibility at the Il4 locus during development to variably regulate IL-4 expression. These events likely contribute to the genetically determined heterogeneity in Th1 responses that underlie susceptibility to many diseases.
Gregory D. Gregory, Shveta S. Raju, Susan Winandy, Melissa A. Brown
Autoimmune diseases are often precipitated by viral infections. Yet our current understanding fails to explain how viruses trigger organ-specific autoimmunity despite thymic tolerance extending to many nonlymphohematopoietic self antigens. Additionally, a key epidemiological finding needs to be explained: In genetically susceptible individuals, early childhood infections seem to predispose them to multiple sclerosis (MS) or type 1 diabetes years or even decades before clinical onset. In the present work, we show that the innate immune system of neonatal mice was sufficient to eliminate an attenuated lymphocytic choriomeningitis virus (LCMV) from most tissues except for the CNS, where the virus persisted in neurons (predisposing virus). Virus-specific cytotoxic T cells (CTLs) were neither deleted nor sufficiently primed to cause disease, but they were efficiently triggered in adulthood upon WT LCMV infection (precipitating virus). This defined sequence of viral infections caused severe CNS inflammation that was histomorphologically reminiscent of rasmussen encephalitis, a fatal human autoimmune disease. Yet disease in mice was mediated by antiviral CTLs targeting an epitope shared by the precipitating virus and the predisposing virus persisting in neurons (déjà vu). Thus the concept of “viral déjà vu” demonstrates how 2 related but independently encountered viral infections can cause organ-specific immune disease without molecular mimicry of self and without breaking self tolerance.
Doron Merkler, Edit Horvath, Wolfgang Bruck, Rolf M. Zinkernagel, Juan Carlos del la Torre, Daniel D. Pinschewer
Why some virus-specific CD8 TCR repertoires are diverse and others restricted or “oligoclonal” has been unknown. We show here that oligoclonality and extreme clonal dominance can be a consequence of T cell cross-reactivity. Lymphocytic choriomeningitis virus (LCMV) and Pichinde virus (PV) encode NP205–212 epitopes that induce different but highly cross-reactive diverse TCR repertoires. Homologous viral challenge of immune mice only slightly skewed the repertoire and enriched for predictable TCR motifs. However, heterologous viral challenge resulted in a narrow oligoclonal repertoire with dominant clones with unpredictable TCR sequences. This shift in clonal dominance varied with the private, i.e., unique, specificity of the host’s TCR repertoire and was simulated using affinity-based computer models. The skewing differences in TCR repertoire following homologous versus heterologous challenge were observed within the same private immune system in mice adoptively reconstituted with memory CD8 T cell pools from the same donor. Conditions driving oligoclonality resulted in an LCMV epitope escape variant in vivo resembling the natural Lassa virus sequence. Thus, T cell oligoclonality, including extremes in clonal dominance, may be a consequence of heterologous immunity and lead to viral escape. This has implications for the design of peptide-based vaccines, which might unintentionally prime for skewed TCR responses to cross-reactive epitopes.
Markus Cornberg, Alex T. Chen, Lee A. Wilkinson, Michael A. Brehm, Sung-Kwon Kim, Claudia Calcagno, Dario Ghersi, Roberto Puzone, Franco Celada, Raymond M. Welsh, Liisa K. Selin
The prevalence of asthma continues to increase. Asthma is caused by a Th2 cell–driven immune response. Its optimal treatment remains a challenge, and a sufficient immunotherapeutic approach to treating asthma has yet to be found. Using a murine asthma model, we show that a single injection of an anti-CD137 (4-1BB) mAb prevents the development of airway hyperreactivity, eosinophilic airway inflammation, excessive mucus production, and elevated IgE during the observation period of 7 weeks. Most importantly, even established disease is completely reversed by anti-CD137 mAb administration. The protection is associated with markedly reduced Th2 cytokine production and increased secretion of the Th1 cytokine IFN-γ. While B lymphocytes are partly depleted, the number of CD8+ T cells is increased. Blockade of IFN-γ and depletion of CD8+ T cells during treatment with anti-CD137 mAb reduces in part but does not abrogate the protective effect of CD137 mAb. In contrast, CD137 mAb–mediated CD4+ T cell anergy is critical for the observed effects, since transfer of CD4+ T cells from CD137 mAb–treated mice conveyed protection. These data demonstrate, for the first time to our knowledge, the capacity of anti-CD137 mAb to ameliorate allergic asthma, and they indicate CD137 as a possible target for therapeutic intervention in this disease.
Tobias Polte, Juergen Foell, Christoph Werner, Heinz-Gerd Hoymann, Armin Braun, Stefan Burdach, obert S. Mittler,, Gesine Hansen
Studies in humans and mice show an important role for Tregs in the control of immunological disorders. The mechanisms underlying the immunosuppressive functions of Tregs are not well understood. Here, we show that CD4+ T cells expressing Foxp3 and membrane-bound TGF-β (TGF-βm+Foxp3+), previously shown to be immunosuppressive in both allergic and autoimmune diseases, activate the Notch1–hairy and enhancer of split 1 (Notch1-HES1) axis in target cells. Soluble TGF-β and cells secreting similar levels of soluble TGF-β were unable to trigger Notch1 activation. Inhibition of Notch1 activation in vivo reversed the immunosuppressive functions of TGF-βm+Foxp3+ cells, resulting in severe allergic airway inflammation. Integration of the TGF-β and Notch1 pathways may be an important mechanism for the maintenance of immune homeostasis in the periphery.
Marina Ostroukhova, Zengbiao Qi, Timothy B. Oriss, Barbara Dixon-McCarthy, rabir Ray,, Anuradha Ray
The Helicobacter pylori neutrophil-activating protein (HP-NAP) is a virulence factor of H. pylori that stimulates in neutrophils high production of oxygen radicals and adhesion to endothelial cells. We report here that HP-NAP is a TLR2 agonist able to induce the expression of IL-12 and IL-23 by neutrophils and monocytes. Addition in culture of HP-NAP, as an immune modulator, to antigen-induced T cell lines resulted in a remarkable increase in the number of IFN-γ–producing T cells and decrease of IL-4–secreting cells, thus shifting the cytokine profile of antigen-activated human T cells from Th2 to a Th1 cytotoxic phenotype. We also found that in vivo HP-NAP elicited an antigen-specific Th1-polarized T cell response in the gastric mucosa of H. pylori–infected patients. These data indicate HP-NAP as an important factor of H. pylori able to elicit cells of the innate immune system to produce IL-12 and IL-23, and they suggest it as a new tool for promoting Th1 immune responses.
Amedeo Amedei, Andrea Cappon, Gaia Codolo, Anna Cabrelle, Alessandra Polenghi, Marisa Benagiano, Elisabetta Tasca, Annalisa Azzurri, Mario Milco D’Elios, Gianfranco Del Prete, Marina de Bernard
The immune system is capable of mounting robust responses against invading pathogens but refrains from attacking self. Many studies have focused on tolerance induction of Th1 cells, whose failure results in development of autoimmune diseases. However, the molecular mechanisms governing tolerance induction in Th2 cells and its relation to allergic responses remain unclear. Here we used both in vivo and in vitro protocols to demonstrate that Th2 cells either containing a mitogen and extracellular kinase kinase 1 (MEKK1) mutant or lacking JNK1 or the E3 ubiquitin ligase Itch cannot be tolerized. In a mouse allergic model, injection of high-dose tolerizing antigen failed to block the development of airway inflammation in Itch–/– mice. This study suggests that MEKK1-JNK signaling regulates Itch E3 ligase–mediated tolerogenic process in Th2 cells. These findings have therapeutic implications for allergic diseases.
K. Venuprasad, Chris Elly, Min Gao, Shahram Salek-Ardakani, Yohsuke Harada, Jun-Li Luo, Chun Yang, Michael Croft, Kazushi Inoue, Michael Karin, Yun-Cai Liu
Human T cell leukemia virus type 1 (HTLV-1) infects both CD4+ and CD8+ lymphocytes, yet it induces adult T cell leukemia/lymphoma (ATLL) that is regularly of the CD4+ phenotype. Here we show that in vivo infected CD4+ and CD8+ T cells displayed similar patterns of clonal expansion in carriers without malignancy. Cloned infected cells from individuals without malignancy had a dramatic increase in spontaneous proliferation, which predominated in CD8+ lymphocytes and depended on the amount of tax mRNA. In fact, the clonal expansion of HTLV-1–positive CD8+ and CD4+ lymphocytes relied on 2 distinct mechanisms — infection prevented cell death in the former while recruiting the latter into the cell cycle. Cell cycling, but not apoptosis, depended on the level of viral-encoded tax expression. Infected tax-expressing CD4+ lymphocytes accumulated cellular defects characteristic of genetic instability. Therefore, HTLV-1 infection establishes a preleukemic phenotype that is restricted to CD4+ infected clones.
David Sibon, Anne-Sophie Gabet, Marc Zandecki, Christiane Pinatel, Julien Thête, Marie-Hélène Delfau-Larue, Samira Rabaaoui, Antoine Gessain, Olivier Gout, Steven Jacobson, Franck Mortreux, Eric Wattel
Emerging evidence suggests critical roles for APCs in suppressing immune responses. Here, we show that zymosan, a stimulus for TLR2 and dectin-1, regulates cytokine secretion in DCs and macrophages to induce immunological tolerance. First, zymosan induces DCs to secrete abundant IL-10 but little IL-6 and IL-12(p70). Induction of IL-10 is dependent on TLR2- and dectin-1–mediated activation of ERK MAPK via a mechanism independent of the activation protein 1 (AP-1) transcription factor c-Fos. Such DCs stimulate antigen-specific CD4+ T cells poorly due to IL-10 and the lack of IL-6. Second, zymosan induces F4-80+ macrophages in the splenic red pulp to secrete TGF-β. Consistent with these effects on APCs, injection of zymosan plus OVA into mice results in OVA-specific T cells that secrete little or no Th1 or Th2 cytokines, but secrete robust levels of IL-10, and are unresponsive to challenge with OVA plus adjuvant. Finally, coinjection of zymosan with OVA plus LPS suppresses the response to OVA via a mechanism dependent on IL-10, TGF-β, and lack of IL-6. Together, our data demonstrate that zymosan stimulates IL-10+IL-12(p70)–IL-6low regulatory DCs and TGF-β+ macrophages to induce immunological tolerance. These data suggest several targets for pharmacological modulation of immune responses in various clinical settings.
Stephanie Dillon, Sudhanshu Agrawal, Kaustuv Banerjee, John Letterio, Timothy L. Denning, Kyra Oswald-Richter, Deborah J. Kasprowicz, Kathryn Kellar, Jeff Pare, Thomas van Dyke, Steven Ziegler, Derya Unutmaz, Bali Pulendran