Epidemiological evidence points to the inverse relationship between microbial exposure and the prevalence of allergic asthma and autoimmune diseases in Westernized countries. The molecular basis for this observation has not yet been completely delineated. Here we report that the administration of certain toll-like receptor (TLR) ligands, via the activation of innate immunity, induces high levels of indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme of tryptophan catabolism in various organs. TLR9 ligand–induced pulmonary IDO activity inhibits Th2-driven experimental asthma. IDO activity expressed by resident lung cells rather than by pulmonary DCs suppressed lung inflammation and airway hyperreactivity. Our results provide a mechanistic insight into the various formulations of the hygiene hypothesis and underscore the notion that activation of innate immunity can inhibit adaptive Th cell responses.
Tomoko Hayashi, Lucinda Beck, Cyprian Rossetto, Xing Gong, Osamu Takikawa, Kenji Takabayashi, David H. Broide, Dennis A. Carson, Eyal Raz
CXC chemokine receptor 3 (CXCR3) is the receptor for the IFN-γ–inducible C-X-C chemokines MIG/CXCL9, IP-10/CXCL10, and I-TAC/CXCL11. CXCR3 is expressed on activated immune cells and proliferating endothelial cells. The role of CXCR3 in fibroproliferation has not been investigated. We examined the role of CXCR3 in pulmonary injury and repair in vivo. CXCR3-deficient mice demonstrated increased mortality with progressive interstitial fibrosis relative to WT mice. Increased fibrosis occurred without increased inflammatory cell recruitment. CXCR3 deficiency resulted in both a reduced early burst of IFN-γ production and decreased expression of CXCL10 after lung injury. We identified a relative deficiency in lung NK cells in the unchallenged CXCR3-deficient lung and demonstrated production of IFN-γ by WT lung NK cells in vivo following lung injury. The fibrotic phenotype in the CXCR3-deficient mice was significantly reversed following administration of exogenous IFN-γ or restoration of endogenous IFN-γ production by adoptive transfer of WT lymph node and spleen cells. Finally, pretreatment of WT mice with IFN-γ–neutralizing Ab’s enhanced fibrosis following lung injury. These data demonstrate a nonredundant role for CXCR3 in limiting tissue fibroproliferation and suggest that this effect may be mediated, in part, by the innate production of IFN-γ following lung injury.
Dianhua Jiang, Jiurong Liang, Jennifer Hodge, Bao Lu, Zhou Zhu, Shuang Yu, Juan Fan, Yunfei Gao, Zhinan Yin, Robert Homer, Craig Gerard, Paul W. Noble
Angiotensin I–converting enzyme (ACE) inhibitors are thought to lower blood pressure in hypertensive patients, mainly by decreasing angiotensin II (Ang II) formation. Chymase, a human mast cell protease, has recently been proposed to play a role in blood pressure regulation because of its Ang II–forming activity. Here we show that the predominant chymase mRNA species in the mouse aorta are those for types 4 and 5 isoforms, and that both are efficient Ang II–forming enzymes. Evaluation of ACE-dependent and ACE-independent Ang II–forming pathways in mast cell–deficient (Kitw/Kitw-v) mice and their mast cell–sufficient littermate (MC+/+) controls revealed that, in contrast to the latter, Kitw/Kitw-v mice fail to express chymase mRNAs in the vasculature and have almost no ACE-independent Ang II–forming activity in either isolated blood vessels or homogenates. Moreover, in MC+/+ but not in Kitw/Kitw-v mice, a contribution of ACE-independent Ang II generation to blood pressure regulation was evident by a 1.6-fold greater maximal reduction in mean arterial pressure with acute ACE inhibition plus AT1 receptor blockade than with ACE inhibition alone. Thus, mast cells are the source of the vascular ACE-independent pathway, and the antihypertensive benefit of combining ACE inhibitor therapy with AT1 receptor antagonist therapy is most likely due to negation of chymase-catalyzed Ang II generation.
Ming Li, Ke Liu, Jan Michalicek, James A. Angus, John E. Hunt, Louis J. Dell’Italia, Michael P. Feneley, Robert M. Graham, Ahsan Husain
Under normal circumstances, the respiratory tract maintains immune tolerance in the face of constant antigen provocation. Using a murine model of tolerance induced by repeated exposure to a low dose of aerosolized antigen, we show an important contribution by CD4+ T cells in the establishment and maintenance of tolerance. The CD4+ T cells expressed both cell surface and soluble TGF-β and inhibited the development of an allergic phenotype when adoptively transferred to naive recipient mice. While cells expressing cell surface TGF-β were detectable in mice with inflammation, albeit at a lower frequency compared with that in tolerized mice, only those from tolerized mice expressed FOXP3. Blockade of TGF-β in vitro and in vivo interfered with immunosuppression. Although cells that expressed TGF-β on the cell surface (TGF-β+), as well as the ones that did not (TGF-β–), secreted equivalent levels of soluble TGF-β, only the former were able to blunt the development of an allergic phenotype in mice. Strikingly, separation of the TGF-β+ cells from the rest of the cells allowed the TGF-β– cells to proliferate in response to antigen. We propose a model of antigen-induced tolerance that involves cell-cell contact with regulatory CD4+ T cells that coexpress membrane-bound TGF-β and FOXP3.
Marina Ostroukhova, Carole Seguin-Devaux, Timothy B. Oriss, Barbara Dixon-McCarthy, Liyan Yang, Bill T. Ameredes, Timothy E. Corcoran, Anuradha Ray
We describe a murine model of early pregnancy failure induced by systemic activation of the CD40 immune costimulatory pathway. Although fetal loss involved an NK cell intermediate, it was not due to lymphocyte-mediated destruction of the fetus and placenta. Rather, pregnancy failure resulted from impaired progesterone synthesis by the corpus luteum of the ovary, an endocrine defect in turn associated with ovarian resistance to the gonadotropic effects of prolactin. Pregnancy failure also required the proinflammatory cytokine TNF-α and correlated with the luteal induction of the prolactin receptor signaling inhibitors suppressor of cytokine signaling 1 (Socs1) and Socs3. Such links between immune activation and reproductive endocrine dysfunction may be relevant to pregnancy loss and other clinical disorders of reproduction.
Adrian Erlebacher, Dorothy Zhang, Albert F. Parlow, Laurie H. Glimcher
Ghrelin, a recently described endogenous ligand for the growth hormone secretagogue receptor (GHS-R), is produced by stomach cells and is a potent circulating orexigen, controlling energy expenditure, adiposity, and growth hormone secretion. However, the functional role of ghrelin in regulation of immune responses remains undefined. Here we report that GHS-R and ghrelin are expressed in human T lymphocytes and monocytes, where ghrelin acts via GHS-R to specifically inhibit the expression of proinflammatory anorectic cytokines such as IL-1β, IL-6, and TNF-α. Ghrelin led to a dose-dependent inhibition of leptin-induced cytokine expression, while leptin upregulated GHS-R expression on human T lymphocytes. These data suggest the existence of a reciprocal regulatory network by which ghrelin and leptin control immune cell activation and inflammation. Moreover, ghrelin also exerts potent anti-inflammatory effects and attenuates endotoxin-induced anorexia in a murine endotoxemia model. We believe this to be the first report demonstrating that ghrelin functions as a key signal, coupling the metabolic axis to the immune system, and supporting the potential use of ghrelin and GHS-R agonists in the management of disease-associated cachexia.
Vishwa Deep Dixit, Eric M. Schaffer, Robert S. Pyle, Gary D. Collins, Senthil K. Sakthivel, Ravichandran Palaniappan, James W. Lillard Jr., Dennis D. Taub
Daniele Accapezzato, Vittorio Francavilla, Marino Paroli, Marco Casciaro, Lucia Valeria Chircu, Agostino Cividini, Sergio Abrignani, Mario U. Mondelli, Vincenzo Barnaba
The progeny of T lymphocytes responding to immunization mostly die rapidly, leaving a few long-lived survivors functioning as immune memory. Thus, control of this choice of death versus survival is critical for immune memory. There are indications that reactive radicals may be involved in this death pathway. We now show that, in mice lacking inducible nitric oxide synthase (iNOS), higher frequencies of both CD4 and CD8 memory T cells persist in response to immunization, even when iNOS+/+ APCs are used for immunization. Postactivation T cell death by neglect is reduced in iNOS–/– T cells, and levels of the antiapoptotic proteins Bcl-2 and Bcl-xL are increased. Inhibitors of the iNOS-peroxynitrite pathway also enhance memory responses and block postactivation death by neglect in both mouse and human T cells. However, early primary immune responses are not enhanced, which suggests that altered survival, rather than enhanced activation, is responsible for the persistent immunity observed. Thus, in primary immune responses, iNOS in activated T cells autocrinely controls their susceptibility to death by neglect to determine the level of persisting CD4 and CD8 T cell memory, and modulation of this pathway can enhance the persistence of immune memory in response to vaccination.
Monika Vig, Smita Srivastava, Usha Kandpal, Hadassah Sade, Virginia Lewis, Apurva Sarin, Anna George, Vineeta Bal, Jeannine M. Durdik, Satyajit Rath
T cell reactivity to minor histocompatibility (mH) antigens is responsible for rejection of HLA-matched allografts, limiting the effectiveness of transplantation for the treatment of end-stage organ failure. The deadbox gene Dby is located on the Y chromosome and encodes an mH antigen that prompts rejection of male tissues by female mice. Establishing a network of regulatory T (Treg) cells that is capable of coercing naive cells to adopt a tolerant phenotype offers an attractive strategy for immune intervention in such deleterious immune responses. While various approaches have successfully induced a dominant form of transplantation tolerance, they share the propensity to provoke chronic, incomplete activation of T cells. By identifying the T cell receptor (TCR) contact sites of the dominant epitope of the Dby gene product, we have designed an altered peptide ligand (APL) that delivers incomplete signals to naive T cells from A1 ∞ RAG1–/– mice that are transgenic for a complementary TCR. Administration of this APL to female transgenic mice polarizes T cells toward a regulatory phenotype, securing a form of dominant tolerance to male skin grafts that is capable of resisting rejection by naive lymphocytes. Our results demonstrate that incomplete signaling through the TCR may establish a network of Treg cells that may be harnessed in the service of transplantation tolerance.
Tse-Ching Chen, Herman Waldmann, Paul J. Fairchild
Administration of an agonistic anti-CD28 mAb paradoxically inhibits donor T cell expansion and prevents graft-versus-host disease (GVHD) in mice. Here we examined the mechanism of anti-CD28–mediated immunosuppression and found that anti-CD28 mAb activated, rather than blocked, CD28-mediated signaling in vivo. Anti-CD28 treatment prevented GVHD by selectively depleting alloantigen-activated donor T cells through apoptosis but spared the T cells that did not recognize recipient alloantigens. Overexpression of Bcl-xL did not protect T cells from depletion and did not affect GVHD prevention after anti-CD28 treatment. Depletion of activated T cells mediated through CD28 did not depend on the expression of death receptors Fas and TNF receptors type I and II, but both the depletion of activated T cells and the suppressive effect of anti-CD28 mAb on GVHD lethality required donor-derived IFN-γ production. This study demonstrates that agonistic Ab’s specific for the CD28 costimulatory molecule may be used as novel therapeutic agents to abrogate pathogenic T cell responses by selective depletion of activated T cells.
Xue-Zhong Yu, Michael H. Albert, Paul J. Martin, Claudio Anasetti