In a strategy to specifically target complement inhibitors to sites of complement activation and disease, recombinant fusion proteins consisting of a complement inhibitor linked to a C3 binding region of complement receptor (CR) 2 were prepared and characterized. Natural ligands for CR2 are C3 breakdown products deposited at sites of complement activation. Fusion proteins were prepared consisting of a human CR2 fragment linked to either the N terminus or C terminus of soluble forms of the membrane complement inhibitors decay accelerating factor (DAF) or CD59. The targeted complement inhibitors bound to C3-opsonized cells, and all were significantly more effective (up to 20-fold) than corresponding untargeted inhibitors at protecting target cells from complement. CR2 fusion proteins also inhibited CR3-dependent adhesion of U937 cells to C3 opsonized erythrocytes, indicating a second potential anti-inflammatory mechanism of CR2 fusion proteins, since CR3 is involved in endothelial adhesion and diapedesis of leukocytes at inflammatory sites. Finally, the in vivo validity of the targeting strategy was confirmed by the demonstration that CR2-DAF, but not soluble DAF, targets to the kidney in mouse models of lupus nephritis that are associated with renal complement deposition.
Hongbin Song, Chun He, Christian Knaak, Joel M. Guthridge, V. Michael Holers, Stephen Tomlinson
IL-10 is a pleiotropic cytokine that inhibits several immune parameters, including Th1 cell–mediated immune responses, antigen presentation, and antigen-specific T cell proliferation. Recent data implicate IL-10 as a mediator of suppression of cell-mediated immunity induced by exposure to UVB radiation (280–320 nm). To investigate the effects of IL-10 on the cutaneous immune system, we engineered transgenic mice that overexpress viral IL-10 (vIL-10) in the epidermis. vIL-10 transgenic mice demonstrated a reduced number of I-A+ epidermal and dermal cells and fewer I-A+ hapten-bearing cells in regional lymph nodes after hapten painting of the skin. Reduced CD80 and CD86 expression by I-A+ epidermal cells was also observed. vIL-10 transgenic mice demonstrated a smaller delayed-type hypersensitivity response to allogeneic cells upon challenge but had normal contact hypersensitivity to an epicutaneously applied hapten. Fresh epidermal cells from vIL-10 transgenic mice showed a decreased ability to stimulate allogeneic T cell proliferation, as did splenocytes. Additionally, chronic exposure of mice to UVB radiation led to the development of fewer skin tumors in vIL-10 mice than in WT controls, and vIL-10 transgenic mice had increased splenic NK cell activity against YAC-1targets. These findings support the concept that IL-10 is an important regulator of cutaneous immune function.
Wanhong Ding, Stefan Beissert, Liang Deng, Edward Miranda, Christopher Cassetty, Kristina Seiffert, Kristina L. Campton, Zhengmin Yan, George F. Murphy, Jeffrey A. Bluestone, Richard D. Granstein
Antimicrobial peptides are effector molecules of the innate immune system and contribute to host defense and regulation of inflammation. The human cathelicidin antimicrobial peptide LL-37/hCAP-18 is expressed in leukocytes and epithelial cells and secreted into wound and airway surface fluid. Here we show that LL-37 induces angiogenesis mediated by formyl peptide receptor–like 1 expressed on endothelial cells. Application of LL-37 resulted in neovascularization in the chorioallantoic membrane assay and in a rabbit model of hind-limb ischemia. The peptide directly activates endothelial cells, resulting in increased proliferation and formation of vessel-like structures in cultivated endothelial cells. Decreased vascularization during wound repair in mice deficient for CRAMP, the murine homologue of LL-37/hCAP-18, shows that cathelicidin-mediated angiogenesis is important for cutaneous wound neovascularization in vivo. Taken together, these findings demonstrate that LL-37/hCAP-18 is a multifunctional antimicrobial peptide with a central role in innate immunity by linking host defense and inflammation with angiogenesis and arteriogenesis.
Rembert Koczulla, Georges von Degenfeld, Christian Kupatt, Florian Krötz, Stefan Zahler, Torsten Gloe, Katja Issbrücker, Pia Unterberger, Mohamed Zaiou, Corinna Lebherz, Alexander Karl, Philip Raake, Achim Pfosser, Peter Boekstegers, Ulrich Welsch, Pieter S. Hiemstra, Claus Vogelmeier, Richard L. Gallo, Matthias Clauss, Robert Bals
The absence of immune defects that occurs in the syndrome of long-term nonprogressive (LTNP) HIV infection offers insights into the pathophysiology of HIV-induced immune disease. The (H[F/S]RIG)2 domain of viral protein R (Vpr) induces apoptosis and may contribute to HIV-induced T cell depletion. We demonstrate a higher frequency of R77Q Vpr mutations in patients with LTNP than in patients with progressive disease. In addition, T cell infections using vesicular stomatitis virus G (VSV-G) pseudotyped HIV-1 Vpr R77Q result in less (P = 0.01) T cell death than infections using wild-type Vpr, despite similar levels of viral replication. Wild-type Vpr-associated events, including procaspase-8 and -3 cleavage, loss of mitochondrial transmembrane potential (Δψm), and DNA fragmentation factor activation are attenuated by R77Q Vpr. These data highlight the pathophysiologic role of Vpr in HIV-induced immune disease and suggest a novel mechanism of LTNP.
Julian J. Lum, Oren J. Cohen, Zilin Nie, Joel G. Weaver, Timothy S. Gomez, Xiao-Jian Yao, David Lynch, André A. Pilon, Nanci Hawley, John E. Kim, Zhaoxia Chen, Michael Montpetit, Jaime Sanchez-Dardon, Eric A. Cohen, Andrew D. Badley
Stat3 plays an essential role in IL-10 signaling pathways. A myeloid cell-specific deletion of Stat3 resulted in inflammatory cytokine production and development of chronic enterocolitis with enhanced Th1 responses in mice. In this study, we analyzed the mechanism by which a Stat3 deficiency in myeloid cells led to the induction of chronic enterocolitis in vivo. Even in the absence of Stat1, which is essential for IFN-γ signaling pathways, Stat3 mutant mice developed chronic enterocolitis. TNF-α/Stat3 double-mutant mice developed severe chronic enterocolitis with enhanced Th1 cell development. IL-12p40/Stat3 double-mutant mice, however, showed normal Th1 responses and no inflammatory change in the colon. RAG2/Stat3 double-mutant mice did not develop enterocolitis, either. These findings indicate that overproduction of IL-12p40, which induces potent Th1 responses, is essential for the development of chronic enterocolitis in Stat3 mutant mice. Furthermore, enterocolitis was significantly improved and IFN-γ production by T cells was reduced in TLR4/Stat3 double-mutant mice, indicating that TLR4-mediated recognition of microbial components triggers aberrant IL-12p40 production by myeloid cells, leading to the development of enterocolitis. Thus, this study clearly established a sequential innate and acquired immune mechanism for the development of Th1-dependent enterocolitis.
Masaya Kobayashi, Mi-Na Kweon, Hirotaka Kuwata, Robert D. Schreiber, Hiroshi Kiyono, Kiyoshi Takeda, Shizuo Akira
Azathioprine and its metabolite 6-mercaptopurine (6-MP) are immunosuppressive drugs that are used in organ transplantation and autoimmune and chronic inflammatory diseases such as Crohn disease. However, their molecular mechanism of action is unknown. In the present study, we have identified a unique and unexpected role for azathioprine and its metabolites in the control of T cell apoptosis by modulation of Rac1 activation upon CD28 costimulation. We found that azathioprine and its metabolites induced apoptosis of T cells from patients with Crohn disease and control patients. Apoptosis induction required costimulation with CD28 and was mediated by specific blockade of Rac1 activation through binding of azathioprine-generated 6-thioguanine triphosphate (6-Thio-GTP) to Rac1 instead of GTP. The activation of Rac1 target genes such as mitogen-activated protein kinase kinase (MEK), NF-κB, and bcl-xL was suppressed by azathioprine, leading to a mitochondrial pathway of apoptosis. Azathioprine thus converts a costimulatory signal into an apoptotic signal by modulating Rac1 activity. These findings explain the immunosuppressive effects of azathioprine and suggest that 6-Thio-GTP derivates may be useful as potent immunosuppressive agents in autoimmune diseases and organ transplantation.
Imke Tiede, Gerhard Fritz, Susanne Strand, Daniela Poppe, Radovan Dvorsky, Dennis Strand, Hans Anton Lehr, Stefan Wirtz, Christoph Becker, Raja Atreya, Jonas Mudter, Kai Hildner, Brigitte Bartsch, Martin Holtmann, Richard Blumberg, Henning Walczak, Heiko Iven, Peter R. Galle, Mohammad Reza Ahmadian, Markus F. Neurath
Experimental autoimmune uveitis (EAU) is a disease of the neural retina induced by immunization with retinal antigens, such as interphotoreceptor retinoid-binding protein (IRBP) and arrestin (retinal soluble antigen, S-Ag). EAU serves as a model for human autoimmune uveitic diseases associated with major histocompatibility complex (HLA) genes, in which patients exhibit immunological responses to retinal antigens. Here we report the development of a humanized EAU model in HLA transgenic (TG) mice. HLA-DR3, -DR4, -DQ6, and -DQ8 TG mice were susceptible to IRBP-induced EAU. Importantly, HLA-DR3 TG mice developed severe EAU with S-Ag, to which wild-type mice are highly resistant. Lymphocyte proliferation was blocked by anti-HLA antibodies, confirming that antigen is functionally presented by the human MHC molecules. Disease could be transferred by immune cells with a Th1-like cytokine profile. Antigen-specific T cell repertoire, as manifested by responses to overlapping peptides derived from S-Ag or IRBP, differed from that of wild-type mice. Interestingly, DR3 TG mice, but not wild-type mice, recognized an immunodominant S-Ag epitope between residues 291 and 310 that overlaps with a region of S-Ag recognized by uveitis patients. Thus, EAU in HLA TG mice offers a new model of uveitis that should represent human disease more faithfully than currently existing models.
Giuseppina Pennesi, Mary J. Mattapallil, Shu-Hui Sun, Dody Avichezer, Phyllis B. Silver, Zaruhi Karabekian, Chella S. David, Paul A. Hargrave, J. Hugh McDowell, W. Clay Smith, Barbara Wiggert, Larry A. Donoso, Chi-Chao Chan, Rachel R. Caspi
Death receptor–mediated activation-induced apoptosis of antigen-specific T cells is a major mechanism of peripheral tolerance induction and immune homeostasis. Failure to undergo activation-induced cell death (AICD) is an important underlying cause of many autoimmune diseases. Thus, enhancing the T cell’s own suicide mechanism may provide an efficient therapy for the treatment of autoimmune diseases. Bisindolylmaleimide VIII (Bis VIII), a PKC inhibitor, can sensitize T cells for death receptor–induced apoptosis and thus can inhibit the development of T cell–mediated autoimmune disease in vivo. In this study, we have analyzed the functional consequences of accelerated suicide for a protective CD8+ T cell–mediated immune response. Our data indicate that CD8+ T cells are sensitized by Bis VIII to AICD, both in vitro and in vivo. The sensitizing effect of Bis VIII appears to be mediated by specific downmodulation of the antiapoptotic molecule cellular FLICE-like inhibitory protein (cFLIPL). Importantly, Bis VIII administration during an acute lymphocytic choriomeningitis virus (LCMV) infection causes the depletion of virus-specific CD8+ T cells and subsequently impaired cytotoxicity and virus clearance. We conclude that resistance to death receptor–induced apoptosis is crucial for the efficient induction of a protective immune response, and that Bis VIII–based immunotherapies have to be applied under well-controlled conditions to avoid the induction of immune incompetence and the inability to respond to pathogen infection.
Christoph Wasem, Diana Arnold, Leslie Saurer, Nadia Corazza, Sabine Jakob, Simon Herren, Claudio Vallan, Christoph Mueller, Thomas Brunner
During ascent to high altitude and pulmonary edema, the alveolar epithelial cells (AEC) are exposed to hypoxic conditions. Hypoxia inhibits alveolar fluid reabsorption and decreases Na,K-ATPase activity in AEC. We report here that exposure of AEC to hypoxia induced a time-dependent decrease of Na,K-ATPase activity and a parallel decrease in the number of Na,K-ATPase α1 subunits at the basolateral membrane (BLM), without changing its total cell protein abundance. These effects were reversible upon reoxygenation and specific, because the plasma membrane protein GLUT1 did not decrease in response to hypoxia. Hypoxia caused an increase in mitochondrial reactive oxygen species (ROS) levels that was inhibited by antioxidants. Antioxidants prevented the hypoxia-mediated decrease in Na,K-ATPase activity and protein abundance at the BLM. Hypoxia-treated AEC deficient in mitochondrial DNA (ρ0 cells) did not have increased levels of ROS, nor was the Na,K-ATPase activity inhibited. Na,K-ATPase α1 subunit was phosphorylated by PKC in hypoxia-treated AEC. In AEC treated with a PKC-ζ antagonist peptide or with the Na,K-ATPase α1 subunit lacking the PKC phosphorylation site (Ser-18), hypoxia failed to decrease Na,K-ATPase abundance and function. Accordingly, we provide evidence that hypoxia decreases Na,K-ATPase activity in AEC by triggering its endocytosis through mitochondrial ROS and PKC-ζ–mediated phosphorylation of the Na,K-ATPase α1 subunit.
Laura A. Dada, Navdeep S. Chandel, Karen M. Ridge, Carlos Pedemonte, Alejandro M. Bertorello, Jacob I. Sznajder
Among infectious agents, measles virus (MV) remains a scourge responsible for 1 million deaths per year and is a leading cause of childhood deaths in developing countries. Although MV infection itself is not commonly lethal, MV-induced suppression of the immune system results in a greatly increased susceptibility to opportunistic bacterial infections that are largely responsible for the morbidity and mortality associated with this disease. Despite its clinical importance, the underlying mechanisms of MV-induced immunosuppression remain unresolved. To begin to understand the basis of increased susceptibility to bacterial infections during MV infection, we inoculated transgenic mice expressing the MV receptor, CD46, with MV and Listeria monocytogenes. We found that MV-infected mice were more susceptible to infection with Listeria and that this corresponded with significantly decreased numbers of macrophages and neutrophils in the spleen and substantial defects in IFN-γ production by CD4+ T cells. The reduction in CD11b+ macrophages and IFN-γ–producing T cells was due to reduced proliferative expansion and not to enhanced apoptosis or to altered distribution of these cells between spleen, blood, and the lymphatic system. These results document that MV infection can suppress both innate and adaptive immune responses and lead to increased susceptibility to bacterial infection.
Mark K. Slifka, Dirk Homann, Antoinette Tishon, Robb Pagarigan, Michael B.A. Oldstone