Generation of neutralizing mouse anti-mouse IL-18 antibodies for inhibition of inflammatory responses in vivo

MAIT cells are imprinted by the microbiota in early life and promote tissue repair

How early-life colonization and subsequent exposure to the microbiota affect long-term tissue immunity remains poorly understood. Here, we show that the development of mucosal-associated invariant T (MAIT) cells relies on a specific temporal window, after which MAIT cell development is permanently impaired. This imprinting depends on early-life exposure to defined microbes that synthesize riboflavin-derived antigens. In adults, cutaneous MAIT cells are a dominant population of interleukin-17A (IL-17A)-producing lymphocytes, which display a distinct transcriptional signature and can subsequently respond to skin commensals in an IL-1-, IL-18-, and antigen-dependent manner. Consequently, local activation of cutaneous MAIT cells promotes wound healing. Together, our work uncovers a privileged interaction between defined members of the microbiota and MAIT cells, which sequentially controls both tissue-imprinting and subsequent responses to injury.

Commensal-specific T cell plasticity promotes rapid tissue adaptation to injury

Barrier tissues are primary targets of environmental stressors and are home to the largest number of antigen-experienced lymphocytes in the body, including commensal-specific T cells. We found that skin-resident commensal-specific T cells harbor a paradoxical program characterized by a type 17 program associated with a poised type 2 state. Thus, in the context of injury and exposure to inflammatory mediators such as interleukin-18, these cells rapidly release type 2 cytokines, thereby acquiring contextual functions. Such acquisition of a type 2 effector program promotes tissue repair. Aberrant type 2 responses can also be unleashed in the context of local defects in immunoregulation. Thus, commensal-specific T cells co-opt tissue residency and cell-intrinsic flexibility as a means to promote both local immunity and tissue adaptation to injury.

Therapeutic potential of dinitrobenzene sulfonic acid (DNBS)-induced colitis in mice by targeting IL-1β and IL-18

Interleukin (IL)-1 and IL-18 belong to the IL-1 family of ligands, and their receptors are members of the IL-1 receptor family. Both cytokines drive an extensive range of pro-inflammatory networks in many cell types using common signal transduction cascades. Anyway, differences in signaling pathways exist. With this aim in mind, we investigated by using transgenic mice the mechanisms through the simultaneous deficiency of both IL-1β and IL-18 could be more protective compared to blocking the single cytokine IL-1β or IL-18 during colitis. Colitis was provoked in mice by instillation of dinitrobenzene sulfonic acid (DNBS) in the colon. The results indicated that single knockout (KO) mice of IL-1β or IL-18, and double KO mice of both IL-1β and IL-18 were hyporesponsive to DNBS-induced colitis compared to wild type (WT) mice, in which double KO were less sensitive than single KO mice. Moreover, treatment with Anakinra (IL-1R antagonist) also ameliorated colitis, in views of macroscopic and histological alteration, infiltration of neutrophils or Th1 cells, oxidative and nitrosative stress. Anakinra more significantly reduced cyclooxygenase (COX-2) and nuclear factor (NF-κB) levels as well as IKB-α degradation compared to blocking IL-18. On the contrary, the absence of IL-18 reduced p-ERK and p-p38 mitogen-activated protein kinase (MAPKs) in a more significant way compared to blocking IL-1β. Thus, the double KO increased the protective effects against colon inflammation maybe because different converging inflammatory pathways are being inhibited. In conclusion, the blocking of both IL-1β and IL-18 function may be advantageous in the treatment of IBD or inflammatory diseases.

Dysregulated IL-18 Is a Key Driver of Immunosuppression and a Possible Therapeutic Target in the Multiple Myeloma Microenvironment

Tumor-promoting inflammation and avoiding immune destruction are hallmarks of cancer. Here, we demonstrate that the pro-inflammatory cytokine interleukin (IL)-18 is critically involved in these hallmarks in multiple myeloma (MM). Mice deficient for IL-18 were remarkably protected from Vk^∗MYC MM progression in a CD8⁺ T cell-dependent manner. The MM-niche-derived IL-18 drove generation of myeloid-derived suppressor cells (MDSCs), leading to accelerated disease progression. A global transcriptome analysis of the immune microenvironment in 73 MM patients strongly supported the negative impact of IL-18-driven MDSCs on T cell responses. Strikingly, high levels of bone marrow plasma IL-18 were associated with poor overall survival in MM patients. Furthermore, our preclinical studies suggested that IL-18 could be a potential therapeutic target in MM.

ESAT-6-dependent cytosolic pattern recognition drives noncognate tuberculosis control in vivo

IFN-γ is a critical mediator of host defense against Mycobacterium tuberculosis (Mtb) infection. Antigen-specific CD4+ T cells have long been regarded as the main producer of IFN-γ in tuberculosis (TB), and CD4+ T cell immunity is the main target of current TB vaccine candidates. However, given the recent failures of such a TB vaccine candidate in clinical trials, strategies to harness CD4-independent mechanisms of protection should be included in future vaccine design. Here, we have reported that noncognate IFN-γ production by Mtb antigen-independent memory CD8+ T cells and NK cells is protective during Mtb infection and evaluated the mechanistic regulation of IFN-γ production by these cells in vivo. Transfer of arenavirus- or protein-specific CD8+ T cells or NK cells reduced the mortality and morbidity rates of mice highly susceptible to TB in an IFN-γ-dependent manner. Secretion of IFN-γ by these cell populations required IL-18, sensing of mycobacterial viability, Mtb protein 6-kDa early secretory antigenic target-mediated (ESAT-6-mediated) cytosolic contact, and activation of NLR family pyrin domain-containing protein 3 (NLRP3) inflammasomes in CD11c+ cell subsets. Neutralization of IL-18 abrogated protection in susceptible recipient mice that had received noncognate cells. Moreover, improved Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine-induced protection was lost in the absence of ESAT-6-dependent cytosolic contact. Our findings provide a comprehensive mechanistic framework for antigen-independent IFN-γ secretion in response to Mtb with critical implications for future intervention strategies against TB.

Identifying the initiating events of anti-Listeria responses using mice with conditional loss of IFN-γ receptor subunit 1 (IFNGR1)

Although IFN-γ is required for resolution of Listeria monocytogenes infection, the identities of the IFN-γ-responsive cells that initiate the process remain unclear. We addressed this question using novel mice with conditional loss of IFN-γR (IFNGR1). Itgax-cre(+)Ifngr1(f/f) mice with selective IFN-γ unresponsiveness in CD8α(+) dendritic cells displayed increased susceptibility to infection. This phenotype was due to the inability of IFN-γ-unresponsive CD8α(+) dendritic cells to produce the initial burst of IL-12 induced by IFN-γ from TNF-α-activated NK/NKT cells. The defect in early IL-12 production resulted in increased IL-4 production that established a myeloid cell environment favoring Listeria growth. Neutralization of IL-4 restored Listeria resistance in Itgax-cre(+)Ifngr1(f/f) mice. We also found that Itgax-cre(+)Ifngr1(f/f) mice survived infection with low-dose Listeria as the result of a second wave of IL-12 produced by Ly6C(hi) monocytes. Thus, an IFN-γ-driven cascade involving CD8α(+) dendritic cells and NK/NKT cells induces the rapid production of IL-12 that initiates the anti-Listeria response.

IL-18 inhibits growth of murine orthotopic prostate carcinomas via both adaptive and innate immune mechanisms

Interleukin(IL)-18 is a pleiotrophic cytokine with functions in immune modulation, angiogenesis and bone metabolism. In this study, the potential of IL-18 as an immunotherapy for prostate cancer (PCa) was examined using the murine model of prostate carcinoma, RM1 and a bone metastatic variant RM1(BM)/B4H7-luc. RM1 and RM1(BM)/B4H7-luc cells were stably transfected to express bioactive IL-18. These cells were implanted into syngeneic immunocompetent mice, with or without an IL-18-neutralising antibody (αIL-18, SK113AE4). IL-18 significantly inhibited the growth of both subcutaneous and orthotopic RM1 tumors and the IL-18 neutralizing antibody abrogated the tumor growth-inhibition. In vivo neutralization of interferon-gamma (IFN-γ) completely eliminated the anti-tumor effects of IL-18 confirming an essential role of IFN-γ as a down-stream mediator of the anti-tumor activity of IL-18. Tumors from mice in which IL-18 and/or IFN-γ was neutralized contained significantly fewer CD4⁺ and CD8⁺ T cells than those with functional IL-18. The essential role of adaptive immunity was demonstrated as tumors grew more rapidly in RAG1^−/− mice or in mice depleted of CD4⁺ and/or CD8⁺ cells than in normal mice. The tumors in RAG1^−/− mice were also significantly smaller when IL-18 was present, indicating that innate immune mechanisms are involved. IL-18 also induced an increase in tumor infiltration of macrophages and neutrophils but not NK cells. In other experiments, direct injection of recombinant IL-18 into established tumors also inhibited tumor growth, which was associated with an increase in intratumoral macrophages, but not T cells. These results suggest that local IL-18 in the tumor environment can significantly potentiate anti-tumor immunity in the prostate and clearly demonstrate that this effect is mediated by innate and adaptive immune mechanisms.

Decreased susceptibility of mice to infection with Listeria monocytogenes in the absence of interleukin-18

The induction of proinflammatory cytokines such as gamma interferon (IFN-gamma) and tumor necrosis factor alpha is crucial for the early control of bacterial infections. Since interleukin-18 (IL-18) acts as a potent inducer of IFN-gamma, it might play an important role in the induction of a protective immune response in listeriosis. We used a murine model of systemic Listeria monocytogenes infection to study the immune response to these intracellular bacteria in the absence of IL-18. For this purpose, IL-18-deficient mice and mice treated with anti-IL-18 neutralizing antibody were infected with L. monocytogenes, and their innate and adaptive immune responses were compared to those of control mice. Unexpectedly, we found that mice deficient in IL-18 were partially resistant to primary infection with L. monocytogenes. At day 3 after infection, the numbers of listeriae in the livers and spleens of control mice were up to 500 times higher than those in IL-18-deficient or anti-IL-18 antibody-treated mice. In addition, the level of proinflammatory cytokines was markedly reduced in IL-18-deficient mice. Enhanced resistance to L. monocytogenes infection in IL-18-deficient mice was accompanied by increased numbers of leukocytes and reduced apoptosis in the spleen 48 to 72 h after infection. In contrast, control and IL-18-deficient mice showed no significant differences in their abilities to mount a protective L. monocytogenes-specific T-cell response.

Both IL-12 and IL-18 contribute to small intestinal Th1-type immunopathology following oral infection with Toxoplasma gondii, but IL-12 is dominant over IL-18 in parasite control

Oral infection of C57BL/6 mice with Toxoplasma gondii results in small intestinal Th1-type immunopathology mediated by local production of IFN-gamma, TNF-alpha, and NO. To analyze whether the proinflammatory cytokines IL-12 and IL-18 play a role in the induction of immunopathology, IL-12p35/p40(-/-) and IL-18(-/-) mice were orally infected with T. gondii. Wild-type mice developed massive necrosis in their small intestines and died 7-10 days post infection. Even though IL-12p35/40(-/-) mice did not develop the necrosis they all died between day 9 and 11 after infection. In contrast, 50% of IL-18(-/-) mice died during the acute phase of infection. Compared to wild-type mice, IL-12p35/p40(-/-) but not IL-18(-/-) mice showed significantly higher parasite numbers in their small intestines and significantly higher numbers of parasite-associated inflammatory foci in their livers. IFN-gamma production was similar in infected wild-type and IL-18(-/-) mice but significantly decreased in IL-12p35/p40(-/-) mice. Treatment of mice with anti-IL-12- or anti-IL-18 antibodies after infection prevented the development of intestinal necrosis. These results reveal that both IL-12 and IL-18 play an important role in the development of intestinal immunopathology following oral infection with T. gondii. However, IL-12 is dominant over IL-18 in the host defense against parasite replication. Therefore, neutralization of IL-18 (rather than TNF-alpha, IL-12, and IFN-gamma) may be a safe strategy for the treatment of Th1-associated diseases.

An animal model of hemophagocytic lymphohistiocytosis (HLH): CD8+ T cells and interferon gamma are essential for the disorder

Hemophagocytic lymphohistiocytosis (HLH) is a rare disorder with familial and acquired forms. The familial form is associated with mutations in the perforin gene and both forms are associated with severe defects in lymphocyte cytotoxic function. We examined perforin-deficient mice as a model of HLH in order to gain insight into this poorly understood disorder. While these mice do not spontaneously develop HLH-like symptoms, we found that they manifest all of the features of HLH after infection with lymphocytic choriomeningitic virus (LCMV). Following LCMV infection, perforin-deficient mice develop fever, splenomegaly, pancytopenia, hypertriglyceridemia, hypofibrinogenemia, and elevation of multiple serum cytokine levels, and hemophagocytosis is evident in many tissues. Investigation into how this phenotype develops has revealed that CD8+ T cells, but not natural killer (NK) cells, are necessary for the development of this disorder. Cytokine neutralization studies have revealed that interferon gamma (IFNgamma) is uniquely essential as well. Finally, the excessive amount of IFNgamma seen in affected mice appears to be driven by increased antigen presentation to CD8+ T cells. These studies provide insight into the pathophysiology of HLH, and provide new targets for specific therapeutic intervention in this fatal disorder.

Regulation and Phenotype of an Innate Th1 Cell: Role of Cytokines and the p38 Kinase Pathway

We have explored the phenotype and regulation of Th1 cell activation by the cytokines IL-12 and IL-18. We demonstrate that these two cytokines selectively induce IFN-gamma in a differentiated Th1 cell population through the previously described p38 mitogen-activated protein (MAP) kinase pathway. Using a highly selective p38 MAP kinase inhibitor, we demonstrate that it is possible to block IFN-gamma induction from activated, differentiated Th1 cells via p38 MAP kinase without disrupting the activation and differentiation of naive T cells or the proliferation of naive or differentiated T cells. In addition, IL-12 and IL-18 provide an Ag and IL-2-independent survival signal to this uniquely differentiated Th1 cell population. We hypothesize that this Ag-independent survival of Th1 cells may participate in an innate inflammatory loop with monocytes at the sites of chronic inflammation. In addition, p38 MAP kinase inhibition of this cytokine-regulated pathway may be a unique mechanism to inhibit chronic inflammation without disruption of Ag-driven activation and function of naive T cells.

Treatment of T cell-dependent experimental colitis in SCID mice by local administration of an adenovirus expressing IL-18 antisense mRNA

Recent studies have shown that IL-18, a pleiotropic cytokine that augments IFN-gamma production, is produced by intestinal epithelial cells and lamina propria cells from patients with Crohn's disease. In this study, we show that IL-18 is strongly expressed by intestinal epithelial cells in a murine model of Crohn's disease induced by transfer of CD62L+ CD4+ T cells into SCID mice. To specifically down-regulate IL-18 expression in this model, we constructed an E1/E3-deleted adenovirus expressing IL-18 antisense mRNA, denoted Ad-asIL-18, and demonstrated the capacity of such a vector to down-regulate IL-18 expression in colon-derived DLD-1 cells and RAW264.7 macrophages. Local administration of the Ad-asIL-18 vector to SCID mice with established colitis led to transduction of epithelial cells and caused a significant suppression of colitis activity, as assessed by a newly developed endoscopic analysis system for colitis. Furthermore, treatment with Ad-asIL-18 induced a significant suppression of histologic colitis activity and caused suppression of mucosal IFN-gamma production, whereas IFN-gamma production by spleen T cells was unaffected. Taken together, these data indicate an important role for IL-18 in the effector phase of a T cell-dependent murine model of colitis and suggest that strategies targeting IL-18 expression may be used for the treatment of patients with Crohn's disease.