NKT cell cytokine imbalance in murine diabetes mellitus

TNF superfamily receptor OX40 triggers invariant NKT cell pyroptosis and liver injury

Tissue-resident immune cells play a key role in local and systemic immune responses. The liver, in particular, hosts a large number of invariant natural killer T (iNKT) cells, which are involved in diverse immune responses. However, the mechanisms that regulate survival and homeostasis of liver iNKT cells are poorly defined. Here we have found that liver iNKT cells constitutively express the costimulatory TNF superfamily receptor OX40 and that OX40 stimulation results in massive pyroptotic death of iNKT cells, characterized by the release of potent proinflammatory cytokines that induce liver injury. This OX40/NKT pyroptosis pathway also plays a key role in concanavalin A-induced murine hepatitis. Mechanistically, we demonstrated that liver iNKT cells express high levels of caspase 1 and that OX40 stimulation activates caspase 1 via TNF receptor-associated factor 6-mediated recruitment of the paracaspase MALT1. We also found that activation of caspase 1 in iNKT cells results in processing of pro-IL-1β to mature IL-1β as well as cleavage of the pyroptotic protein gasdermin D, which generates a membrane pore-forming fragment to produce pyroptotic cell death. Thus, our study has identified OX40 as a death receptor for iNKT cells and uncovered a molecular mechanism of pyroptotic cell death. These findings may have important clinical implications in the development of OX40-directed therapies.

Enalapril treatment increases T cell number and promotes polarization towards M1-like macrophages locally in diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of longstanding diabetes affecting up to 30% of all diabetes patients and is the main cause of end-stage kidney disease globally. Current standard treatment e.g. ACE-inhibitors like enalapril merely offers a delay in the progression leading to DN. Herein, we describe in two preclinical models evidence to local effects on the inflammatory signatures after intervention treatment with enalapril which provides enhanced understanding of the mechanism of ACE inhibitors. Enalapril transiently reduced albuminuria in both the db/db and the STZ-induced DN models with established disease, without modulating the HbA1c%. Albuminuria was strongly associated with loss of leukocytes, particularly B cells, but also of sub-populations of macrophages and CD4(+) T cells. The remaining kidney macrophages were polarized into a M2-like sub-population with reduced surface expression of the M1-like macrophage marker CD11c and enhanced expression of galectin-3. Enalapril treatment counteracted the reduction of leukocytes in the diabetic kidney towards levels noted in the non-diabetic kidney. Particularly, a subset of macrophages was increased and a clear expansion of CD4(+) and CD8(+) T cells was observed. However, enalapril failed to modulate the B cell compartment. Interestingly, enalapril treatment resulted in a re-polarization of the macrophages towards a M1-like phenotype characterized by elevated levels of CD11c with moderate down-regulation of the M2 marker galectin-3. The data demonstrate that ACE inhibition in pre-clinical models of DN shows a transient beneficial effect on albuminuria which is unexpectedly associated with restoration of T cells and M1-like macrophages in the kidney.

Tissue-targeted therapy of autoimmune diabetes using dendritic cells transduced to express IL-4 in NOD mice

A deficit in IL-4 production has been previously reported in both diabetic human patients and non-obese diabetic (NOD) mice. In addition, re-introducing IL-4 into NOD mice systemically, or as a transgene, led to a beneficial outcome in most studies. Here, we show that prediabetic, 12-week old female NOD mice have a deficit in IL-4 expression in the pancreatic lymph nodes (PLN) compared to age-matched diabetes-resistant NOD.B10 mice. By bioluminescence imaging, we demonstrated that the PLN was preferentially targeted by bone marrow-derived dendritic cells (DCs) following intravenous (IV) administration. Following IV injection of DCs transduced to express IL-4 (DC/IL-4) into 12-week old NOD mice, it was possible to significantly delay or prevent the onset of hyperglycemia. We then focused on the PLN to monitor, by microarray analysis, changes in gene expression induced by DC/IL-4 and observed a rapid normalization of the expression of many genes, that were otherwise under-expressed compared to NOD.B10 PLN. The protective effect of DC/IL-4 required both MHC and IL-4 expression by the DCs. Thus, adoptive cellular therapy, using DCs modified to express IL-4, offers an effective, tissue-targeted cellular therapy to prevent diabetes in NOD mice at an advanced stage of pre-diabetes, and may offer a safe approach to consider for treatment of high risk human pre-diabetic patients.

Innate and adaptive immunity and the pathophysiology of psoriasis

Psoriasis is considered to be a genetically programmed disease of dysregulated inflammation, which is driven and maintained by multiple components of the immune system. The pathologic collaboration between innate immunity (mediated by antigen-presenting cells and natural killer T lymphocytes) and acquired immunity (mediated by T lymphocytes) results in the production of cytokines, chemokines, and growth factors that contribute to the inflammatory infiltrate seen in psoriatic plaques. This overview of the pathophysiology of psoriasis describes these events, and recent developments that have contributed to our understanding of the role of immune function in psoriasis. These developments include the creation of useful animal models and identification of new receptors and lymphocyte subtypes that may participate in the development of this chronic disease.

Pathogenesis of nonalcoholic steatohepatitis (NASH)

Nonalcoholic fatty liver disease (NAFLD) represents a spectrum of liver diseases that range from hepatic steatosis at the most clinically benign end of the spectrum, through an intermediate lesion, nonalcoholic steatohepatitis (NASH), to cirrhosis at the opposite extreme. Epidemiology studies have estimated that about 20-30% of adults in the United States and other Western countries have NAFLD, and of these about 10% (2-3% of adults) meet the diagnostic criteria of NASH. Studies of animals and humans with obesity-related fatty liver disease have revealed much about the mechanisms that mediate this common pathology. The pathogenesis of NASH is multifactorial and includes insulin resistance, excessive intracellular fatty acids, oxidant stress, mitochondrial dysfunction and the role of innate immunity. This review will briefly discuss the epidemiology of NAFLD and focus on current understanding of the pathogenesis of NASH.

Expansion and hyperactivity of CD1d-restricted NKT cells during the progression of systemic lupus erythematosus in (New Zealand Black x New Zealand White)F1 mice

CD1d-restricted NKT cells expressing invariant TCR alpha-chain rearrangements (iNKT cells) have been reported to be deficient in humans with a variety of autoimmune syndromes and in certain strains of autoimmune mice. In addition, injection of mice with alpha-galactosylceramide, a specific glycolipid agonist of iNKT cells, activates these T cells and ameliorates autoimmunity in several different disease models. Thus, deficiency and reduced function in iNKT cells are considered to be risk factors for the development of such diseases. In this study we report that the development of systemic lupus erythematosus in (New Zealand Black (NZB) x New Zealand White (NZW))F(1) mice was paradoxically associated with an expansion and activation of iNKT cells. Although young (NZB x NZW)F(1) mice had normal levels of iNKT cells, these expanded with age and became phenotypically and functionally hyperactive. Activation of iNKT cells in (NZB x NZW)F(1) mice in vivo or in vitro with alpha-galactosylceramide indicated that the immunoregulatory role of iNKT cells varied over time, revealing a marked increase in their potential to contribute to production of IFN-gamma with advancing age and disease progression. This evolution of iNKT cell function during the progression of autoimmunity may have important implications for the mechanism of disease in this model of systemic lupus erythematosus and for the development of therapies using iNKT cell agonists.

An integrated view of suppressor T cell subsets in immunoregulation

The immune system evolved to protect organisms from a virtually infinite variety of disease-causing agents but to avoid harmful responses to self. Because immune protective mechanisms include the elaboration of potent inflammatory molecules, antibodies, and killer cell activation--which together can not only destroy invading microorganisms, pathogenic autoreactive cells, and tumors, but also mortally injure normal cells--the immune system is inherently a "double-edged sword" and must be tightly regulated. Immune response regulation includes homeostatic mechanisms intrinsic to the activation and differentiation of antigen-triggered immunocompetent cells and extrinsic mechanisms mediated by suppressor cells. This review series will focus on recent advances indicating that distinct subsets of regulatory CD4+ and CD8+ T cells as well as NK T cells control the outgrowth of potentially pathogenic antigen-reactive T cells and will highlight the evidence that these suppressor T cells may play potentially important clinical roles in preventing and treating immune-mediated disease. Here we provide a historical overview of suppressor cells and the experimental basis for the existence of functionally and phenotypically distinct suppressor subsets. Finally, we will speculate on how the distinct suppressor cell subsets may function in concert to regulate immune responses.

The immunoregulatory role of CD1d-restricted natural killer T cells in disease

Natural killer T (NKT) cells constitute a T cell subpopulation that shares several characteristics with NK cells. NKT cells are characterized by a narrow T cell antigen receptor (TCR) repertoire, recognize glycolipid antigen in the context of the monomorphic CD1d antigen-presenting molecule, and have the unique capacity to rapidly produce large amounts of both T helper (Th) 1 and Th2 cytokines. Important roles of NKT cells have now been demonstrated in the regulation of autoimmune, allergic, antimicrobial, and antitumor immune responses. Here, we review the immunoregulatory role of NKT cells in disease and discuss NKT cell based immunotherapeutic strategies.

TNF receptor-associated factor 6 deficiency during hemopoiesis induces Th2-polarized inflammatory disease

Toll-like receptors (TLR) initiate rapid innate immune responses by recognizing microbial products. These events in turn lead to the development of an efficient adaptive immune response through the up-regulation of a number of costimulatory molecules, including members of the TNF/TNFR superfamily, on the surface of an APC. TNFR-associated factor 6 (TRAF6) is a common signaling adapter used by members of both the TNFR and the TLR/IL-1R superfamilies, and as such plays a critical role in the development of immune responses. As TRAF6-deficient mice die prematurely, we generated chimeras reconstituted with TRAF6-deficient fetal liver cells to analyze functions of TRAF6 in vivo in the hemopoietic compartment. We found that TRAF6-deficient chimeras develop a progressive lethal inflammatory disease associated with massive organ infiltration and activation of CD4(+) T cells in a Th2-polarized phenotype, and a defect in IL-18 responsiveness. When recombination-activating gene 2(-/-) blastocysts were complemented with TRAF6-deficient embryonic stem cells, a marked elevation of activated CD4(+) T cells and progressive inflammatory disease were also observed. Moreover, T cell activation and lethal inflammation were not reversed in mixed chimeric mice generated from normal and TRAF6-deficient fetal liver cells. These results suggest that deletion of TRAF6 induces a dominant Th2-type polarized autoimmune response. Therefore, in addition to playing a critical role in innate and adaptive immunity, TRAF6 is likely to play a previously unrecognized role in the maintenance of self-tolerance.

Apoptosis and transplantation tolerance

Self-tolerance is maintained by several mechanisms including deletion (via apoptosis) and regulation. Acquired tolerance to allogeneic tissues and organs exploits similar strategies. One key difference between alloantigens and peptide antigens is the enormous number of T cells that are alloreactive. Accumulating evidence suggests that in the face of this large mass of potentially graft-destructive T cells, tolerance requires an initial wave of deletion. This creates a more level playing field in which a smaller number of regulatory T cells can then act to maintain an established tolerant state. Deletion of alloreactive T cells by apoptosis actively promotes immunoregulation as well, by interfering with proinflammatory maturation of antigen presenting cells. This article reviews the immune response to alloantigens, the development and use of both necrotic and apoptotic means of cell death during the evolution of the immune response, and the likely role and mechanisms by which apoptosis promotes, and may even be required for, transplantation tolerance.

CD8+ tumor-infiltrating lymphocytes are primed for Fas-mediated activation-induced cell death but are not apoptotic in situ

Induction of Fas-mediated activation-induced cell death in antitumor T cells has been hypothesized to permit tumor escape from immune destruction. Several laboratories have proposed that expression of Fas ligand (L) by tumor is the basis for this form of T cell tolerance. In this study, we characterized murine tumor-infiltrating lymphocytes (TIL) for activation status, cell cycle status, level of apoptosis, cytokine secretion, and proliferative capacity. TILs express multiple activation markers (circa CD69, CD95L, CD122, and LFA-1) and contain IL-2 and IFN-gamma mRNAs, but are neither cycling nor apoptotic in situ. In addition, TIL are dramatically suppressed in proliferative response and do not secrete IL-2 and IFN-gamma. However, upon purification and activation in vitro, TIL secrete high levels of IL-2 and IFN-gamma, enter S phase, and then die by Fas-mediated apoptosis. Activation by injection of anti-TCR Ab or IL-2 into tumor-bearing mice induced TIL entrance into S phase preceding apoptosis, showing that TIL have functional TCR-mediated signal transduction in situ. Our data demonstrate that TIL, not tumor, express both Fas and FasL, are arrested in G(1), do not secrete cytokine in situ, and, upon activation in vitro and in vivo, rapidly die by activation-induced cell death.

Decreases in interleukin-4 secretion by invariant CD4(-)CD8(-)V alpha 24J alpha Q T cells in peripheral blood of patientswith relapsing-remitting multiple sclerosis

The cytokine profile of invariant CD4(-)CD8(-)V alpha 24J alpha Q T cells from patients with multiple sclerosis (MS) was compared with that of healthy controls. CD4(-)CD8(-)V alpha 24(+) T cells from the peripheral blood of 12 patients with relapsing-remitting MS (RR-MS), 5 patients with progressive MS (CP-MS), and 9 control individuals were directly sorted into single wells and expanded in vitro for analysis of IL-4 and IFN-gamma secretion; 315 V alpha 24J alpha Q T cell clones were generated and their T cell receptor (TCR) sequenced. T cell functionality was determined by examining cytokine secretion upon TCR cross-linking. RR-MS patients exhibited lower frequencies of IL-4 secreting CD4(-)CD8(-)V alpha 24J alpha Q T cell clones than patients with CP-MS and controls. No differences in IFN-gamma secretion were observed between the groups. An IL-4 positive cytokine profile could be correlated to the cloning efficiency of the V alpha 24J alpha Q T cells. We conclude that alterations in cytokine secretion patterns of CD4(-)CD8(-)V alpha 24J alpha Q T cells may influence the immune system and thus contribute to relapsing-remitting MS.

The role of different subsets of T regulatory cells in controlling autoimmunity

T regulatory cells-in addition to clonal deletion and anergy-are essential for the downregulation of T cell responses to both foreign and self antigens, and for the prevention of autoimmunity. Recent progress has been made in characterising the different subsets of T regulatory cells, the factors that drive their differentiation, and their mode of action. The resolution of these mechanisms will make it possible to use T regulatory cells therapeutically in human autoimmune diseases.

Mice bearing late-stage tumors have normal functional systemic T cell responses in vitro and in vivo

Immune suppression in tumor-bearing hosts is considered to be one factor causally associated with the growth of antigenic tumors. Support for this hypothesis has come from reports that spleen T cells in tumor-bearing mice are deficient in either priming or effector phase functions. We have reexamined this hypothesis in detail using multiple murine tumor models, including transplantable adenocarcinoma, melanoma, sarcoma, and thymoma, and also a transgenic model of spontaneous breast carcinoma. In both in vitro and in vivo assays of T cell function (proliferation, cytokine production, induction of CD8+ alloreactive CTL, and development of anti-keyhole limpet hemocyanin CD4+ T cells, rejection of allogeneic or syngeneic regressor tumors, respectively) we show that mice bearing sizable tumor burdens are not systemically suppressed and do not have diminished T cell functions. Therefore, if immune suppression is a causal function in the growth of antigenic tumor, the basis for escape from immune destruction is likely to be dependent upon tumor-induced T cell dysfunction at the site of tumor growth.