Severe CD4 T cell-mediated immunopathology in murine schistosomiasis is dependent on IL-12p40 and correlates with high levels of IL-17

C57BL/6 mice infected with the helminth Schistosoma mansoni develop small hepatic granulomas around parasite eggs, but concomitant immunization with soluble schistosome egg Ags (SEA) in CFA (SEA/CFA) causes marked exacerbation of the lesions in a Th1-dominated environment characterized by high levels of IFN-gamma. We explored the cause of the severe immunopathology by using IL-12p40(-/-) and IL-12p35(-/-) mice. SEA/CFA-immunized IL-12p40(-/-) mice, incapable of making IL-12 or IL-23, were completely resistant to high pathology, and their SEA-stimulated lymphoid cells failed to secrete significant IFN-gamma or IL-17. In contrast, SEA/CFA-immunized IL-12p35(-/-) mice, able to make IL-23 but not IL-12, developed severe lesions that correlated with high levels of IL-17, low IFN-gamma, and an expansion of activated CD4 T cells with a CD44(high)/CD62L(low) memory phenotype. In vivo administration of neutralizing anti-IL-17 mAb markedly inhibited hepatic granulomatous inflammation. Importantly, CBA mice, a naturally high pathology strain, also displayed elevated IL-17 levels comparable to those seen in the SEA/CFA-immunized BL/6 mice, and their lesions were similarly reduced by in vivo treatment with anti-IL-17. Our findings indicate that an IL-17-producing T cell population, likely driven by IL-23, significantly contributes to severe immunopathology in schistosomiasis.     

CD4 T cells producing pro-inflammatory interleukin-17 mediate high pathology in schistosomiasis

In murine schistosomiasis mansoni, pronounced CD4 T cell-mediated, egg-induced, hepato-intestinal immunopathology and death, whether genetically determined or elicited experimentally, are associated with failure to down-regulate a net pro-inflammatory immune response. Important evidence contributing to this notion comes from the observation that immunization with schistosome egg antigens in CFA (SEA/CFA) causes low pathology C57BL/6 mice to develop an exacerbated form of disease and death in a cytokine milieu characterized by elevated interferon (IFN)-gamma levels. Since such a pro-inflammatory environment presumes a signaling pathway involving interleukin (IL)-12, the SEA/CFA immunization model was used to examine the extent of hepatic immunopathology in the absence of this cytokine. Surprisingly, the IL-12p40 subunit was an absolute requirement for the development of exacerbated disease, whereas the IL-12p35 subunit was not. Moreover, significantly elevated in vitro production of IL-17, but not of IFN-gamma, correlated with the high pathology, and neutralization of IL-17 in vivo resulted in a significant reduction of hepatic inflammation. Our findings clearly demonstrate the pathogenic potential of the novel IL-17-producing T cell subpopulation (ThIL-17), previously shown to mediate chronic inflammation in autoimmune disease. They also imply that IL-23, but not IL-12, is the critical signal necessary to support the pro-inflammatory ThIL-17 subset involved in high pathology schistosomiasis.     

The pathogenic Th17 cell response to major schistosome egg antigen is sequentially dependent on IL-23 and IL-1β

CBA/J mice infected with the helminth Schistosoma mansoni develop severe CD4 T cell-mediated hepatic granulomatous inflammation against parasite eggs associated with a robust Th17 cell response. We investigated the requisites for Th17 cell development using novel CD4 T cells expressing a transgenic TCR specific for the major Sm-p40 egg Ag, which produce IL-17 when stimulated with live schistosome eggs. Neutralization of IL-23 or blockade of the IL-1 receptor, but not IL-6 neutralization, abrogated egg-induced IL-17 secretion by transgenic T cells, whereas exogenous IL-23 or IL-1β reconstituted their ability to produce IL-17 when stimulated by syngeneic IL-12p40-deficient dendritic cells. Kinetic analysis demonstrated that IL-17 production was initiated by IL-23 and amplified by IL-1β. Significantly, schistosome-infected IL-12p40-deficient or IL-1R antagonist-treated CBA/J mice developed markedly reduced hepatic immunopathology with a dampened egg Ag-specific IL-17 response. These results demonstrate that the IL-23-IL-1-IL-17 axis has a central role in the development of severe schistosome egg-induced immunopathology.     

Concurrent bacterial stimulation alters the function of helminth-activated dendritic cells, resulting in IL-17 induction

Infection with schistosome helminths is associated with granulomatous inflammation that forms around parasite eggs trapped in host tissues. In severe cases, the resulting fibrosis can lead to organ failure, portal hypertension, and fatal bleeding. Murine studies identified IL-17 as a critical mediator of this immunopathology, and mouse strains that produce high levels of IL-17 in response to schistosome infection show increased mortality. In this article, we demonstrate that schistosome-specific IL-17 induction by dendritic cells from low-pathology C57BL/6 mice is normally regulated by their concomitant induction of IL-10. Simultaneous stimulation of schistosome-exposed C57BL/6 dendritic cells with a heat-killed bacterium enabled these cells to overcome IL-10 regulation and induce IL-17, even in wild-type C57BL/6 recipients. This schistosome-specific IL-17 was dependent on IL-6 production by the copulsed dendritic cells. Coimmunization of C57BL/6 animals with bacterial and schistosome Ags also resulted in schistosome-specific IL-17, and this response was enhanced in the absence of IL-10-mediated immune regulation. Together, our data suggest that the balance of pro- and anti-inflammatory cytokines that determines the severity of pathology during schistosome infection can be influenced not only by host and parasite, but also by concurrent bacterial stimulation.     

STAT3 and NF-kappaB signal pathway is required for IL-23-mediated IL-17 production in spontaneous arthritis animal model IL-1 receptor antagonist-deficient mice

IL-23 is a heterodimeric cytokine composed of a p19 subunit and the p40 subunit of IL-12. IL-23 has proinflammatory activity, inducing IL-17 secretion from activated CD4(+) T cells and stimulating the proliferation of memory CD4(+) T cells. We investigated the pathogenic role of IL-23 in CD4(+) T cells in mice lacking the IL-1R antagonist (IL-1Ra(-/-)), an animal model of spontaneous arthritis. IL-23 was strongly expressed in the inflamed joints of IL-1Ra(-/-) mice. Recombinant adenovirus expressing mouse IL-23 (rAd/mIL-23) significantly accelerated this joint inflammation and joint destruction. IL-1beta further increased the production of IL-23, which induced IL-17 production and OX40 expression in splenic CD4(+) T cells of IL-1Ra(-/-) mice. Blocking IL-23 with anti-p19 Ab abolished the IL-17 production induced by IL-1 in splenocyte cultures. The process of IL-23-induced IL-17 production in CD4(+) T cells was mediated via the activation of Jak2, PI3K/Akt, STAT3, and NF-kappaB, whereas p38 MAPK and AP-1 did not participate in the process. Our data suggest that IL-23 is a link between IL-1 and IL-17. IL-23 seems to be a central proinflammatory cytokine in the pathogenesis of this IL-1Ra(-/-) model of spontaneous arthritis. Its intracellular signaling pathway could be useful therapeutic targets in the treatment of autoimmune arthritis.     

Interleukin-23 restores immunity to Mycobacterium tuberculosis infection in IL-12p40-deficient mice and is not required for the development of IL-17-secreting T cell responses

Host control of Mycobacterium tuberculosis is dependent on the activation of CD4+ T cells secreting IFN-gamma and their recruitment to the site of infection. The development of more efficient vaccines against tuberculosis requires detailed understanding of the induction and maintenance of T cell immunity. Cytokines important for the development of cell-mediated immunity include IL-12 and IL-23, which share the p40 subunit and the IL-12Rbeta1 signaling chain. To explore the differential effect of IL-12 and IL-23 during M. tuberculosis infection, we used plasmids expressing IL-23 (p2AIL-23) or IL-12 (p2AIL-12) alone in dendritic cells or macrophages from IL-12p40(-/-) mice. In the absence of the IL-12/IL-23 axis, immunization with a DNA vaccine expressing the M. tuberculosis Ag85B induced a limited Ag-specific T cell response and no control of M. tuberculosis infection. Co-delivery of p2AIL-23 or p2AIL-12 with DNA85B induced strong proliferative and IFN-gamma-secreting T cell responses equivalent to those observed in wild-type mice immunized with DNA85B. This response resulted in partial protection against aerosol M. tuberculosis; however, the protective effect was less than in wild-type mice owing to the requirement for IL-12 or IL-23 for the optimal expansion of IFN-gamma-secreting T cells. Interestingly, bacillus Calmette-Guérin immune T cells generated in the absence of IL-12 or IL-23 were deficient in IFN-gamma production, but exhibited a robust IL-17 secretion associated with a degree of protection against pulmonary infection. Therefore, exogenous IL-23 can complement IL-12 deficiency for the initial expansion of Ag-specific T cells and is not essential for the development of potentially protective IL-17-secreting T cells.     

Compromised humoral and delayed-type hypersensitivity responses in IL-23-deficient mice

The heterodimeric cytokine IL-23 consists of a private cytokine-like p19 subunit and a cytokine receptor-like subunit, p40, which is shared with IL-12. Previously reported IL-12p40-deficient mice have profound immune defects resulting from combined deficiency in both IL-12 and IL-23. To address the effects of specific IL-23 deficiency, we generated mice lacking p19 by gene targeting. These mice display no overt abnormalities but mount severely compromised T-dependent humoral immune responses. IL-23p19(-/-) mice produce strongly reduced levels of Ag-specific Igs of all isotypes, but mount normal T-independent B cell responses. In addition, delayed type hypersensitivity responses are strongly impaired in the absence of IL-23, indicating a defect at the level of memory T cells. T cells stimulated with IL-23-deficient APCs secrete significantly reduced amounts of the proinflammatory cytokine IL-17, and IL-23-deficient mice phenotypically resemble IL-17-deficient animals. Thus, IL-23 plays a critical role in T cell-dependent immune responses, and our data provide further support for the existence of an IL-23/IL-17 axis of communication between the adaptive and innate parts of the immune system.     

IL-23 compensates for the absence of IL-12p70 and is essential for the IL-17 response during tuberculosis but is dispensable for protection and antigen-specific IFN-gamma responses if IL-12p70 is available

IL-12p70 induced IFN-gamma is required to control Mycobacterium tuberculosis growth; however, in the absence of IL-12p70, an IL-12p40-dependent pathway mediates induction of IFN-gamma and initial bacteriostatic activity. IL-23 is an IL-12p40-dependent cytokine containing an IL-12p40 subunit covalently bound to a p19 subunit that is implicated in the induction of CD4 T cells associated with autoimmunity and inflammation. We show that in IL-23 p19-deficient mice, mycobacterial growth is controlled, and there is no diminution in either the number of IFN-gamma-producing Ag-specific CD4 T cells or local IFN-gamma mRNA expression. Conversely, there is an almost total loss of both IL-17-producing Ag-specific CD4 T cells and local production of IL-17 mRNA in these mice. The absence of IL-17 does not alter expression of the antimycobacterial genes, NO synthase 2 and LRG-47, and the absence of IL-23 or IL-17, both of which are implicated in mediating inflammation, fails to substantially affect the granulomatous response to M. tuberculosis infection of the lung. Despite this redundancy, IL-23 is required to provide a moderate level of protection in the absence of IL-12p70, and this protection correlates with a requirement for IL-23 in the IL-12p70-independent induction of Ag-specific, IFN-gamma-producing CD4 T cells. We also show that IL-23 is required for the induction of an IL-17-producing Ag-specific phenotype in naive CD4 T cells in vitro and that absence of IL-12p70 promotes an increase in the number of IL-17-producing Ag-specific CD4 T cells both in vitro and in vivo.     

Deficiency in TLR2 but not in TLR4 impairs dendritic cells derived IL-10 responses to schistosome antigens

The purpose of this study was to observe the diverse functions of Toll-like receptors (TLRs) in responses to specific schistosome antigens. Bone marrow-derived dendritic cells (BMDCs) from TLR2-deficient (TLR2(-/-)) or TLR4-deficient (TLR4(-/-)) mice were activated with soluble schistosomule antigen (SSA) or soluble egg antigen (SEA). TLR2 mRNA expression was significantly increased in B6 BMDCs following SEA stimulation. TLR2-deficient BMDCs showed enhanced MHCII expression following SSA and SEA stimulation. TLR2-deficient but not TLR4-deficient BMDC failed to produce IL-12p70 and IL-10 in response to schistosome antigens. TLR2-deficient BMDCs induced a stronger CD4(+) T cell proliferative response. IL-4 and IL-10 expression was inhibited in CD4(+) T cells primed with TLR2-deficient BMDCs, while enhanced in TLR4-deficient BMDCs-primed CD4(+) T cells. These results suggest that TLR2 is essential for the establishment of the DC production of IL-12p70 and IL-10.     

Cutting edge: IL-23 cross-regulates IL-12 production in T cell-dependent experimental colitis

Although IL-12 and IL-23 share the common p40 subunit, IL-23, rather than IL-12, seems to drive the pathogenesis of experimental autoimmune encephalomyelitis and arthritis, because IL-23/p19 knockout mice are protected from disease. In contrast, we describe in this study that newly created LacZ knockin mice deficient for IL-23 p19 were highly susceptible for the development of experimental T cell-mediated TNBS colitis and showed even more severe colitis than wild-type mice by endoscopic and histologic criteria. Subsequent studies revealed that dendritic cells from p19-deficient mice produce elevated levels of IL-12, and that IL-23 down-regulates IL-12 expression upon TLR ligation. Finally, in vivo blockade of IL-12 p40 in IL-23-deficient mice rescued mice from lethal colitis. Taken together, our data identify cross-regulation of IL-12 expression by IL-23 as novel key regulatory pathway during initiation of T cell dependent colitis.     

IL-23 is required for neutrophil homeostasis in normal and neutrophilic mice

IL-23 is secreted by macrophages and dendritic cells in response to microbial products and inflammatory cytokines. IL-23 is a heterodimer composed of the unique IL-23p19 subunit linked to the common p40 subunit that it shares with IL-12. IL-23 is implicated in autoimmune diseases, where it supports the expansion of IL-17A-producing CD4+ Th17 cells. IL-23 also regulates granulopoiesis in a neutrostat regulatory feedback loop through IL-17A-producing neutrophil regulatory (Tn) cells, most of which express gammadelta TCR. This homeostatic system is disrupted in mice lacking adhesion molecules like beta2-integrins (Itgb2-/-) which have defective neutrophil trafficking and neutrophilia. To test the role of IL-23 in the homeostatic regulation of circulating neutrophil numbers, we measured blood neutrophil numbers in p40-deficient (IL12b-/-) mice and found them reduced compared with wild-type mice. IL12b-/-Itgb2-/- mice, lacking beta2-integrins, IL-12, and IL-23 showed significantly blunted neutrophilia compared with Itgb2-/- mice. Treatment of both IL12b-/- and IL12b-/-Itgb2-/- mice with IL-23, but not IL-12, restored circulating neutrophil counts. Serum levels of IL-17A were readily detectable in Itgb2-/- mice, but not in IL12b-/-Itgb2-/- mice, suggesting that IL-17A production is reduced when IL-23 is absent. Similarly, tissue mRNA expression of IL-17A was reduced in IL12b-/-Itgb2-/-mice compared with Itgb2-/- controls. The total number of CD3+ IL-17A-producing Tn cells were significantly reduced in the spleen and lamina propria of IL12b-/-Itgb2-/- mice, with the largest reduction found in gammadelta+ T cells. Our results suggest a prominent role of IL-23 in the regulation of granulopoiesis and the prevalence of IL-17A-producing Tn cells.     

IL-23 provides a limited mechanism of resistance to acute toxoplasmosis in the absence of IL-12

IL-23 and IL-12 are heterodimeric cytokines which share the p40 subunit, but which have unique second subunits, IL-23p19 and IL-12p35. Since p40 is required for the development of the Th1 type response necessary for resistance to Toxoplasma gondii, studies were performed to assess the role of IL-23 in resistance to this pathogen. Increased levels of IL-23 were detected in mice infected with T. gondii and in vitro stimulation of dendritic cells with this pathogen resulted in increased levels of mRNA for this cytokine. To address the role of IL-23 in resistance to T. gondii, mice lacking the p40 subunit (common to IL-12 and IL-23) and mice that lack IL-12 p35 (specific for IL-12) were infected and their responses were compared. These studies revealed that p40(-/-) mice rapidly succumbed to toxoplasmosis, while p35(-/-) mice displayed enhanced resistance though they eventually succumbed to this infection. In addition, the administration of IL-23 to p40(-/-) mice infected with T. gondii resulted in a decreased parasite burden and enhanced resistance. However, the enhanced resistance of p35(-/-) mice or p40(-/-) mice treated with IL-23 was not associated with increased production of IFN-gamma. When IL-23p19(-/-) mice were infected with T. gondii these mice developed normal T cell responses and controlled parasite replication to the same extent as wild-type mice. Together, these studies indicate that IL-12, not IL-23, plays a dominant role in resistance to toxoplasmosis but, in the absence of IL-12, IL-23 can provide a limited mechanism of resistance to this infection.     

IL-12p35 subunit contributes to autoimmunity by limiting IL-27-driven regulatory responses

Contrasting results have emerged from studies performed using IL-12p35(-/-) mice. Animals lacking the IL-12p35 subunit can either be protected from or develop exacerbated autoimmune diseases, intracellular infections, and delayed-type hypersensitivity responses. In this study, we report that mice lacking the IL-12p35 subunit develop a significantly milder Ag-induced arthritis compared with wild-type (WT) mice. Lack of severe inflammation is accompanied by an increase in the mRNA levels of the Ebi-3 and p28 subunits and increased secretion of IL-27 and IL-10. This anti-inflammatory environment contributed to increased differentiation of regulatory T and B cells with intact suppressive function. Furthermore, IL-12p35(-/-) mice display reduced numbers of Th17 cells compared with WT arthritic mice. Neutralization of IL-27, but not the systemic administration of IL-12, restored inflammation and Th17 to levels seen in WT mice. The restoration of disease phenotype after anti-IL-27 administration indicates that the IL-12p35 subunit acts as negative regulator of the developing IL-27 response in this model of arthritis.     

TGF-beta and IL-10 regulation of IFN-gamma produced in Th2-type schistosome granulomas requires IL-12

Interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) regulate CD4+ T cell interferon-gamma (IFN-gamma) secretion in schistosome granulomas. The role of IL-12 was determined using C57BL/6 and CBA mice. C57BL/6 IL-4-/- granuloma cells were stimulated to produce IFN-gamma when cultured with IL-10 or TGF-beta neutralizing monoclonal antibody. In comparison, C57BL/6 wild-type (WT) control granuloma cells produced less IFN-gamma. IL-12, IL-18, and soluble egg antigen stimulated IFN-gamma release from C57BL/6 IL-4-/- and WT mice. IFN-gamma production in C57 IL-4-/- and WT granulomas was IL-12 dependent, because IL-12 blockade partly abrogated IFN-gamma secretion after stimulation. All granuloma cells released IL-12 (p70 and p40), and IL-12 production remained constant after anti-TGF-beta, anti-IL-10, recombinant IL-18, or antigen stimulation. C57 WT and IL-4-/- mouse granuloma cells expressed IL-12 receptor (IL-12R) beta1-subunit mRNA but little beta2 mRNA. TGF-beta or IL-10 blockade did not influence beta1 or beta2 mRNA expression. CBA mouse dispersed granuloma cells released no measurable IFN-gamma, produced IL-12 p70 and little p40, and expressed IL-12R beta2 and little beta1 mRNA. In T helper 2 (Th2) granulomas of C57BL/6 WT and IL-4-/- mice, cells produce IL-12 (for IFN-gamma production) and IL-10 and TGF-beta modulate IFN-gamma secretion via mechanisms independent of IL-12 and IL-12R mRNA regulation. We found substantial differences in control of granuloma IFN-gamma production and IL-12 circuitry in C57BL/6 and CBA mice.     

IL-23 is increased in dendritic cells in multiple sclerosis and down-regulation of IL-23 by antisense oligos increases dendritic cell IL-10 production

IL-23 is a heterodimeric cytokine comprising a p19 subunit associated with the IL-12/23p40 subunit. Like IL-12, IL-23 is expressed predominantly by activated dendritic cells (DCs) and phagocytic cells, and both cytokines induce IFN-gamma secretion by T cells. The induction of experimental autoimmune encephalitis, the animal model of multiple sclerosis (MS), occurs in mice lacking IL-12, but not in mice with targeted disruption of IL-23 or both IL-12 and IL-23. Thus, IL-23 expression in DCs may play an important role in the pathogenesis of human autoimmune diseases such as MS. We quantified the expression of IL-23 in monocyte-derived DCs in MS patients and healthy donors and found that DCs from MS patients secrete elevated amounts of IL-23 and express increased levels of IL-23p19 mRNA. Consistent with this abnormality, we found increased IL-17 production by T cells from MS patients. We then transfected monocyte-derived DCs from healthy donors with antisense oligonucleotides specific for the IL-23p19 and IL-12p35 genes and found potent suppression of gene expression and blockade of bioactive IL-23 and IL-12 production without affecting cellular viability or DCs maturation. Inhibition of IL-23 and IL-12 was associated with increased IL-10 and decreased TNF-alpha production. Furthermore, transfected DCs were poor allostimulators in the MLR. Our results demonstrate that an abnormal Th1 bias in DCs from MS patients related to IL-23 exists, and that antisense oligonucleotides specific to IL-23 can be used for immune modulation by targeting DC gene expression.     

Systemic administration of IL-23 induces potent antitumor immunity primarily mediated through Th1-type response in association with the endogenously expressed IL-12

IL-23, a cytokine, which is composed of the p40 subunit shared with IL-12 and the IL-23-specific p19 subunit, has been shown to preferentially act on Th1 effector/memory CD4+ T cells and to induce their proliferation and IFN-gamma production. The IL-23 is also reported to act on Th17-CD4+ T cells, which are involved in inducing tissue injury. In this study, we examined the antitumor effects associated with systemic administration of IL-23 and their mechanisms in mouse tumor system. Systemic administration of high-dose IL-23 was achieved using in vivo electroporation of IL-23 plasmid DNA into the pretibial muscles of C57BL/6 mice. The IL-23 treatment was associated with significant suppression of the growth of pre-existing MCA205 fibrosarcoma and prolongation of the survival of treated mice without significant toxicity when compared with those of the mice treated with EGFP. Although the therapeutic outcomes were similar to those with the IL-12 treatment, the IL-23 treatment induced characteristic immune responses distinctive to those of IL-12 treatment. The IL-23 administration even at the therapeutic levels did not induce detectable IFN-gamma concentration in the serum. In vivo depletion of CD4+ T cells, CD8+ T cells, or NK cells significantly inhibited the antitumor effects of IL-23. Furthermore, the CD4+ T cells in the lymph nodes in the IL-23-treated mice showed significant IFN-gamma and IL-17 response upon anti-CD3 mAb stimulation in vitro. These results and the ones in the IFN-gamma or IL-12 gene knockout mice suggest that potent antitumor effects of IL-23 treatment could be achieved when the Th1-type response is fully promoted in the presence of endogenously expressed IL-12.     

IL-23-mediated psoriasis-like epidermal hyperplasia is dependent on IL-17A

IL-23 and Th17 cells producing IL-17A and IL-22 are found in excess in skin affected by psoriasis. Previous studies showed that IL-22, but not IL-17A, mediates psoriasis-like epidermal hyperplasia following recombinant murine (rm)IL-23 injections into skin. To further investigate the role of IL-17A, ears of mice were injected with rmIL-23. Investigators blinded to treatment conditions and mouse genotypes measured ear swelling, epidermal thickness, and cytokine expression. In wild-type (WT) mice, rmIL-23 induced ear swelling (p < 0.001, all p values versus saline), epidermal hyperplasia by histology (p < 0.001) and confocal microscopy (p < 0.004), and expression of both IL-17A and IL-22. As expected, rmIL-23 injections into IL-22(-/-) mice resulted in relatively little ear swelling (p < 0.09) and epidermal hyperplasia (p < 0.51 by histology and p < 0.75 by confocal microscopy). Notably, rmIL-23 injections into IL-17A(-/-) mice produced little ear swelling (p < 0.001, versus IL-23-injected WT mice) and epidermal hyperplasia (p < 0.001 by histology and p < 0.005 by confocal microscopy), even though IL-22 was readily induced in these mice. Furthermore, systemic delivery of blocking Abs directed against either IL-22 or IL-17A completely inhibited IL-23-induced epidermal hyperplasia in WT mice. These results demonstrate that IL-17A, like IL-22, is a downstream mediator for IL-23-induced changes in murine skin and that both of these Th17 cytokines are necessary to produce IL-23-mediated skin pathology. IL-17A may represent an attractive therapeutic target in individuals with psoriasis by blocking downstream effects of IL-23.     

IL-23 inhibits osteoclastogenesis indirectly through lymphocytes and is required for the maintenance of bone mass in mice

IL-23 stimulates the differentiation and function of the Th17 subset of CD4(+) T cells and plays a critical role in chronic inflammation. The IL-23 receptor-encoding gene is also an inflammatory disease susceptibility gene. IL-23 shares a common subunit with IL-12, a T cell-dependent osteoclast formation inhibitor, and we found that IL-23 also dose-dependently inhibited osteoclastogenesis in a CD4(+) T lymphocyte-dependent manner. When sufficiently enriched, gammadelta T cells also mediated IL-23 inhibition. Like IL-12, IL-23 acted synergistically with IL-18 to block osteoclastogenesis but, unlike IL-12, IL-23 action depended on T cell GM-CSF production. IL-23 did not mediate IL-12 action although IL-12 induced its expression. Male mice lacking IL-23 (IL-23p19(-/-)) had approximately 30% lower bone mineral density and tibial trabecular bone mass (bone volume (BV)/total volume (TV)) than wild-type littermates at 12 wk and 40% lower BV/TV at 26 wk of age; male heterozygotes also had lower bone mass. Female IL-23p19(-/-) mice also had reduced BV/TV. IL-23p19(-/-) mice had no detectable osteoclast defect in trabecular bone but IL-23p19(-/-) had thinner growth plate hypertrophic and primary spongiosa zones (and, in females, less cartilage remnants) compared with wild type. This suggests increased osteoclast action at and below the growth plate, leading to reduced amounts of mature trabecular bone. Thus, IL-23 inhibits osteoclast formation indirectly via T cells in vitro. Under nonpathological conditions (unlike inflammatory conditions), IL-23 favors higher bone mass in long bones by limiting resorption of immature bone forming below the growth plate.     

IL-23 enhances the inflammatory cell response in Cryptococcus neoformans infection and induces a cytokine pattern distinct from IL-12

IL-23, a heterodimeric cytokine composed of the p40 subunit of IL-12 and a novel p19 subunit, has been shown to be a key player in models of autoimmune chronic inflammation. To investigate the role of IL-23 in host resistance during chronic fungal infection, wild-type, IL-12- (IL-12p35-/-), IL-23- (IL-23p19-/-), and IL-12/IL-23- (p40-deficient) deficient mice on a C57BL/6 background were infected with Cryptococcus neoformans. Following infection, p40-deficient mice demonstrated higher mortality than IL-12p35-/- mice. Reconstitution of p40-deficient mice with rIL-23 prolonged their survival to levels similar to IL-12p35-/- mice. IL-23p19-/- mice showed a moderately reduced survival time and delayed fungal clearance in the liver. Although IFN-gamma production was similar in wild-type and IL-23p19-/- mice, production of IL-17 was strongly impaired in the latter. IL-23p19-/- mice produced fewer hepatic granulomata relative to organ burden and showed defective recruitment of mononuclear cells to the brain. Moreover, activation of microglia cells and expression of IL-1beta, IL-6, and MCP-1 in the brain was impaired. These results show that IL-23 complements the more dominant role of IL-12 in protection against a chronic fungal infection by an enhanced inflammatory cell response and distinct cytokine regulation.     

Schistosome-infected IL-4 receptor knockout (KO) mice, in contrast to IL-4 KO mice, fail to develop granulomatous pathology while maintaining the same lymphokine expression profile.

Th2 lymphocytes have been postulated to play a major role in the immunopathology induced by Schistosoma mansoni infection. Nevertheless, infected IL-4 knockout (KO) and wild-type (wt) mice develop egg granulomas comparable in size. To further investigate the function of the Th2 response in egg pathology we studied IL-4Ralpha-deficient mice, which are nonresponsive to both IL-4 and IL-13. In striking contrast to IL-4 KO animals, infected IL-4Ralpha KO mice developed only minimal hepatic granulomas and fibrosis despite the presence of CD3+ T cells in the residual egg lesions. Moreover, liver lymphokine mRNA levels in these animals and IL-4 KO mice were equivalent. In addition, infected IL-4Ralpha-deficient, IL-4-deficient, and wt animals developed similar egg Ag-specific IgG Ab titers, arguing that CD4-dependent Th activity is intact in KO mice. As expected, IFN-gamma secretion was strongly up-regulated in mesenteric lymph node cultures from both groups of deficient animals, a change reflected in increased serum IgG2a and IgG2b Ab levels. Surprisingly, Th2 cytokine production in infected IL-4Ralpha KO mice was not abolished but was only reduced and resembled that previously documented in IL-4 KO animals. This residual Th2 response is likely to explain the ability of IL-4 KO mice to generate egg granulomas, which cannot be formed in IL-4Ralpha-deficient animals because of their lack of responsiveness to the same cytokine ligands. Taken together, these findings argue that tissue pathology in schistosomiasis requires, in addition to egg-specific CD4+ lymphocytes, a previously unrecognized IL-4Ralpha+ non-T cell effector population.