Interleukin-18 attracts plasmacytoid dendritic cells (DC2s) and promotes Th1 induction by DC2s through IL-18 receptor expression

Bioengineering strategies to enhance the interleukin-18 bioactivity in the modern toolbox of cancer immunotherapy

Cytokines are the first modern immunotherapeutic agents used for activation immunotherapy. Interleukin-18 (IL-18) has emerged as a potent anticancer immunostimulatory cytokine over the past three decades. IL-18, structurally is a stable protein with very low toxicity at biological doses. IL-18 promotes the process of antigen presentation and also enhances innate and acquired immune responses. It can induce the production of proinflammatory cytokines and increase tumor infiltration of effector immune cells to revert the immunosuppressive milieu of tumors. Furthermore, IL-18 can reduce tumorigenesis, suppress tumor angiogenesis, and induce tumor cell apoptosis. These characteristics present IL-18 as a promising option for cancer immunotherapy. Although several preclinical studies have reported the immunotherapeutic potential of IL-18, clinical trials using it as a monotherapy agent have reported disappointing results. These results may be due to some biological characteristics of IL-18. Several bioengineering approaches have been successfully used to correct its defects as a bioadjuvant. Currently, the challenge with this anticancer immunotherapeutic agent is mainly how to use its capabilities in a rational combinatorial therapy for clinical applications. The present study discussed the strengths and weaknesses of IL-18 as an immunotherapeutic agent, followed by comprehensive review of various promising bioengineering approaches that have been used to overcome its disadvantages. Finally, this study highlights the promising application of IL-18 in modern combinatorial therapies, such as chemotherapy, immune checkpoint blockade therapy, cell-based immunotherapy and cancer vaccines to guide future studies, circumventing the barriers to administration of IL-18 for clinical applications, and bring it to fruition as a potent immunotherapy agent in cancer treatment.

Interleukin-18 cytokine in immunity, inflammation, and autoimmunity: Biological role in induction, regulation, and treatment

Interleukin-18 (IL-18) is a potent pro-inflammatory cytokine involved in host defense against infections and regulates the innate and acquired immune response. IL-18 is produced by both hematopoietic and non-hematopoietic cells, including monocytes, macrophages, keratinocytes and mesenchymal cell. IL-18 could potentially induce inflammatory and cytotoxic immune cell activities leading to autoimmunity. Its elevated levels have been reported in the blood of patients with some immune-related diseases, including rheumatoid arthritis, systemic lupus erythematosus, type I diabetes mellitus, atopic dermatitis, psoriasis, and inflammatory bowel disease. In the present review, we aimed to summarize the biological properties of IL-18 and its pathological role in different autoimmune diseases. We also reported some monoclonal antibodies and drugs targeting IL-18. Most of these monoclonal antibodies and drugs have only produced partial effectiveness or complete ineffectiveness in vitro, in vivo and human studies. The ineffectiveness of these drugs targeting IL-18 may be largely due to the loophole caused by the involvement of other cytokines and proteins in the signaling pathway of many inflammatory diseases besides the involvement of IL-18. Combination drug therapies, that focus on IL-18 inhibition, in addition to other cytokines, are highly recommended to be considered as an important area of research that needs to be explored.

Pleiotropic functions of plasmacytoid dendritic cells in the pathogenesis of the rheumatoid arthritis

Rheumatoid arthritis is a chronic autoimmune inflammatory disease with an unclear etiology. The disease is characterized by infiltration of synovial tissue with immune cells, among which there are dendritic cells that play multifaceted roles in the pathogenesis of the disease. Here we shall assume that plasmacytoid dendritic cells are able to change their phenotype under the influence of various stimuli, thereby modulating the course of the disease, contributing to both the development of exacerbations and the induction of remissions depending on the phenotype they have acquired. This property can be used to develop new methods of immunotherapy.

Altered expression of IL-18 binding protein and IL-18 receptor in basophils and mast cells of asthma patients

IL-18 is likely to contribute to asthma. However, little is known regarding the role of IL-18 binding protein (BP) and IL-18 receptor (R) in asthma. Because the action of IL-18 in the body is regulated by IL-18BP and mast cells and basophils are key cell types involved in asthma, we investigated the expression of IL-18, IL-18BP and IL-18R in basophils and mast cells using flow cytometry and a mouse asthma model. We found that among basophils, approximately 53% and 51% were IL-18⁺ , 85% and 81% were IL-18BP⁺ basophils, and 19.8% and 8.6% were IL-18R⁺ in healthy control (HC) and asthmatic blood, respectively. The allergens tested had little effect on the expression of IL-18 and related factors. Only 3.5%, 14.3% and 2.4% of dispersed mast cells expressed IL-18, IL-18BP and IL-18R, respectively, in asthmatic sputum. In a mouse asthma model, OVA-sensitized mice exhibited decreased IL-18BP⁺ but increased IL-18R⁺ basophils in their blood. IL-18 increased the number of basophils but eliminated IL-18BP⁺ basophils in mouse blood. IL-18 increased the number of mast cells and IL-18R⁺ mast cells in the lung as well as increased the mast cell numbers and IL-18BP⁺ mast cells in the bronchoalveolar lavage fluid (BALF) of OVA-sensitized mice. Thus, basophils and mast cells may be involved in asthma pathogenesis via an IL-18-associated mechanism.

Chemokine and chemotactic signals in dendritic cell migration

Dendritic cells (DCs) are professional antigen-presenting cells responsible for the activation of specific T-cell responses and for the development of immune tolerance. Immature DCs reside in peripheral tissues and specialize in antigen capture, whereas mature DCs reside mostly in the secondary lymphoid organs where they act as antigen-presenting cells. The correct localization of DCs is strictly regulated by a large variety of chemotactic and nonchemotactic signals that include bacterial products, DAMPs (danger-associated molecular patterns), complement proteins, lipids, and chemokines. These signals function both individually and in concert, generating a complex regulatory network. This network is regulated at multiple levels through different strategies, such as synergistic interactions, proteolytic processing, and the actions of atypical chemokine receptors. Understanding this complex scenario will help to clarify the role of DCs in different pathological conditions, such as autoimmune diseases and cancers and will uncover new molecular targets for therapeutic interventions.

The involvement of plasmacytoid cells in HIV infection and pathogenesis

Plasmacytoid dendritic cells (pDCs) are a unique dendritic cell subset that are specialized in type I interferon (IFN) production. pDCs are key players in the antiviral immune response and serve as bridge between innate and adaptive immunity. Although pDCs do not represent the main reservoir of the Human Immunodeficiency Virus (HIV), they are a crucial subset in HIV infection as they influence viral transmission, target cell infection and antigen presentation. pDCs act as inflammatory and immunosuppressive cells, thus contributing to HIV disease progression. This review provides a state of art analysis of the interactions between HIV and pDCs and their potential roles in HIV transmission, chronic immune activation and immunosuppression. A thorough understanding of the roles of pDCs in HIV infection will help to improve therapeutic strategies to fight HIV infection, and will further increase our knowledge on this important immune cell subset.

Cytokine Profile in Gout: Inflammation Driven by IL-6 and IL-18?

INTRODUCTION

Gout is considered to be an autoinflammatory disease and the presence of monosodium urate (MSU) crystals stimulates activation of NPRL3 inflammasome and subsequently caspase-1, generating production of active IL-1β and IL-18. However, the association between serum cytokines levels and clinical manifestations of the disease is not yet well understood. We evaluated the serum profile of proinflammatory cytokines (IL-1β, IL-6, IL-8, IL-17A, IL-18, IL-22, and IL-23) and described their relationship with clinical and laboratory data.

METHODOLOGY

Thirty-nine male patients with gout (GG) were assessed for clinical and laboratory variables and cytokine levels were measured by ELISA. For the purposes of comparison, 34 males with no previous history of arthritis were also included in the study (CG).

RESULTS

Seventeen participants (43%) exhibited active arthritis on evaluation. Levels of IL-18 were significantly higher in patients in relation to the CG (p = 0.0013). No statistically significant differences were found between the GG and CG for the other measured cytokines. There was a moderate correlation between IL-18 and ESR (R = 0.43, p = 0.0073), CRP (R = 0.47, p = 0.0025), and serum levels of IL-6 (R = 0.36, p = 0.023). An association was observed between serum levels of IL-6 and the presence of tophi (p = 0.005) and deformities (p = 0.0008), as well as a correlation between this cytokine and ESR (R = 0.41, p = 0.011) and CRP (R = 0.48, p = 0.02).

CONCLUSIONS

IL-18 is associated with inflammatory activity in gout, as well as with IL-6 levels, while IL-6 is associated with clinical and laboratory activity, the presence of tophi and articular deformities, and may be a prognostic marker of this pathology.

Correlation of IL-18 with Tryptase in Atopic Asthma and Induction of Mast Cell Accumulation by IL-18

Interleukin- (IL-) 18 and tryptase were previously reported to relate to asthma, but the correlation between these two potent proinflammatory molecules in asthma and their roles in mast cell accumulation remain uninvestigated. Using flow cytometric analysis technique and ovalbumin- (OVA-) sensitized mouse model, it was found that IL-18 and tryptase levels in the plasma of moderate and severe asthma were elevated, and they correlated well with each other. Tryptase and agonist peptides of protease activated receptor- (PAR-) 2 induced substantial quantity of IL-18 release. IL-18 and tryptase provoked mast cell accumulation in peritoneum of OVA-sensitized mice. OVA-sensitization increased number of IL-18 receptor (R)⁺ mast cells. IL-18 and tryptase induced dramatic increase in IL-18R⁺ mast cells and mean fluorescence intensity (MFI) of IL-18R on mast cells. Moreover, while IL-18 induced an increase in PAR-2⁺ mast cells in nonsensitized mice, IL-18 and tryptase provoked increases in IL-4 and thymic stromal lymphopoietin (TSLP) in the peritoneum of OVA-sensitized mice. In summary, the correlation between IL-18 and tryptase in plasma of patients with asthma indicates close interactions between them, which should be considered for development of anti-IL-18 and antitryptase therapies. Interactions between IL-18 and tryptase may contribute to mast cell recruitment in asthma.

Clinical and laboratory features of fatal rapidly progressive interstitial lung disease associated with juvenile dermatomyositis

OBJECTIVE

Rapidly progressive interstitial lung disease (RP-ILD) is a rare but potentially fatal complication of JDM. The aim of this study was to establish markers for the prediction and early diagnosis of RP-ILD associated with JDM.

METHODS

The clinical records of 54 patients with JDM were retrospectively reviewed: 10 had RP-ILD (7 died, 3 survived), 19 had chronic ILD and 24 were without ILD. Routine tests included a high-resolution CT (HRCT) scan of the chest and measurement of serum levels of creatine phosphokinase, ferritin and Krebs von den Lungen-6 (KL-6). Anti-melanoma differentiation-associated gene 5 (MDA5) antibodies and IL-18 levels were measured by ELISA.

RESULTS

No differences were found in the ratio of juvenile clinically amyopathic DM between the three groups. Initial chest HRCT scan findings were variable and could not distinguish between RP-ILD and chronic ILD. Anti-MDA5 antibodies were positive in all 8 patients with RP-ILD and 10 of 14 with chronic ILD, but none of the patients without ILD. Serum levels of anti-MDA5 antibody, ferritin, KL-6 and IL-18 were significantly higher in the RP-ILD group than in the chronic ILD and non-ILD groups. Serum levels of IL-18 positively correlated with serum KL-6 (R = 0.66, P < 0.001).

CONCLUSION

High serum levels of IL-18, KL-6, ferritin and anti-MDA5 antibodies (e.g. >200 units by ELISA) are associated with RP-ILD. These can be used as an indication for early intensive treatment. Both alveolar macrophages and autoimmunity to MDA5 are possibly involved in the development of RP-ILD associated with JDM.

Human plasmacytoid dendritic cells regulate IFN-α production through activation-induced splicing of IL-18Rα

IFN-α production by pDCs regulates host protection against viruses and is implicated in autoimmune pathology. Human pDCs express high levels of IL-18R, but little is known of its role in pDC function. We report that IL-18R signaling negatively regulates IFN-α production through activation-induced splicing of IL-18Rα in human pDCs. Our data reveal two distinct isoforms of IL-18Rα in human pDCs: the known, full-length receptor (IL-18Rα1) and a novel, truncated variant (IL-18Rα2), which functions as a molecular decoy that competitively inhibits the canonical IL-18Rα1/IL-18Rβ signaling pathway. Whereas NK cells and pDCs both express IL-18Rα1, pDCs express significantly higher levels of IL-18Rα2, resulting in differential responses of these populations to IL-18. Flu exposure increases IL-18Rα1 expression in pDCs, and the blocking of IL-18R enhances pDC production of IFN-α and IP-10; thus, pDCs use activation-induced splicing to regulate IFN-α production in response to flu. These data demonstrate that IL-18R modulates IFN-α release by human pDCs and suggest that IL-18R signaling may represent a promising therapeutic target.

Progression of autoimmune hepatitis is mediated by IL-18-producing dendritic cells and hepatic CXCL9 expression in mice

Clinical manifestations of autoimmune hepatitis (AIH) range from mild chronic to acute, sometimes fulminant hepatitis. However, it is unknown how the progression to fatal hepatitis occurs. We developed a mouse model of fatal AIH by inducing a concurrent loss of forkhead box P3(+) regulatory T cells and programmed cell death-1 (PD-1)-mediated signaling. In this model, dysregulated follicular helper T cells in the spleen are responsible for the induction, and the C-C chemokine receptor 6/C-C chemokine ligand 20 axis is crucial for the migration of these T cells into the liver. Using this fatal AIH model, we aimed to clarify key molecules triggering fatal AIH progression. During progression, T-bet together with interferon (IFN)-γ and C-X-C chemokine receptor (CXCR)3 were highly expressed in the inflamed liver, suggesting helper T (Th)1-type inflammation. T cells that dominantly expanded in the spleen and the inflamed liver were CXCR3-expressing CD8(+) T cells; depletion of these CD8(+) T cells suppressed AIH progression. Expression of one CXCR3 ligand, chemokine (C-X-C motif) ligand (CXCL)9, was elevated in the liver. CXCL9-expressing macrophages/Kupffer cells were colocalized with infiltrating T cells, and in vivo administration of anti-CXCL9 suppressed AIH progression. In addition, serum levels of interleukin (IL)-18, but not IL-1β, were elevated during progression, and dendritic cells in the spleen and liver highly produced IL-18. In vivo administration of anti-IL-18R suppressed the increase of splenic CXCR3(+) T cells and the progression to fatal AIH. Moreover, tumor necrosis factor alpha, but not IFN-γ, was involved in up-regulating CXCL9 in the liver and for increased serum levels of IL-18.

CONCLUSION

These data suggest that, in our mouse model, fatal progression of AIH is mediated by IL-18-dependent differentiation of T cells into Th1 cells and effector T cells, respectively, and that CXCR3-CXCL9 axis-dependent migration of those T cells is crucial for fatal progression.

Lupus nephritis: the evolving role of novel therapeutics

Immune complex accumulation in the kidney is the hallmark of lupus nephritis and triggers a series of events that result in kidney inflammation and injury. Cytotoxic agents and corticosteroids are standard of care for lupus nephritis treatment, but are associated with considerable morbidity and suboptimal outcomes. Recently, there has been interest in using novel biologic agents and small molecules to treat lupus nephritis. These therapies can be broadly categorized as anti-inflammatory (laquinamod, anti-tumor necrosis factor-like weak inducer of apotosis, anti-C5, and retinoids), antiautoimmunity (anti-CD20, anti-interferon α, and costimulatory blockers), or both (anti-interleukin 6 and proteasome inhibitors). Recent lupus nephritis clinical trials applied biologics or small molecules of any category to induction treatment, seeking short-term end points of complete renal response. These trials in general have not succeeded. When lupus nephritis comes to clinical attention during the inflammatory stage of the disease, the autoimmune stage leading to kidney inflammation will have been active for some time. The optimal approach for using novel therapies may be to initially target kidney inflammation to preserve renal parenchyma, followed by suppression of autoimmunity. In this review, we discuss novel lupus nephritis therapies and how they fit into a combinatorial treatment strategy based on the pathogenic stage.

Plasmacytoid dendritic cells in HIV infection

Plasmacytoid dendritic cells (pDCs) are innate immune cells that are specialized to produce interferon-alpha (IFNα) and participate in activating adaptive immune responses. Although IFNα inhibits HIV-1 (HIV) replication in vitro, pDCs may act as inflammatory and immunosuppressive dendritic cells (DCs) rather than classical antigen-presenting cells during chronic HIV infection in vivo, contributing more to HIV pathogenesis than to protection. Improved understanding of HIV-pDC interactions may yield potential new avenues of discovery to prevent HIV transmission, to blunt chronic immune activation and exhaustion, and to enhance beneficial adaptive immune responses. In this chapter we discuss pDC biology, including pDC development from progenitors, trafficking and localization of pDCs in the body, and signaling pathways involved in pDC activation. We focus on the role of pDCs in HIV transmission, chronic disease progression and immune activation, and immunosuppression through regulatory T cell development. Lastly, we discuss potential future directions for the field which are needed to strengthen our current understanding of the role of pDCs in HIV transmission and pathogenesis.

Endothelial function and its implications for cardiovascular and renal disease in systemic lupus erythematosus

Vascular manifestations associated with systemic lupus erythematosus (SLE) span a broad range, including vasculopathy. An understudied pathway of this morbidity is a repair component. Recent studies have elevated the anti-injury biomarkers, adiponectin and membrane endothelial protein C receptor (EPCR), for consideration with roles to antagonize premature atherosclerosis and SLE nephritis, respectively. For example, adiponectin was found to serve as an independent predictor of carotid plaque, and its elevations were persistent over more than one visit. Unexpectedly, this biomarker was present despite clinical quiescence. In vasculopathy as a comorbidity to SLE nephritis, the persistent expression of membrane EPCR at peritubular capillaries may represent a response to the local cues of a deficit of active protein C. Under conditions of unresolved morbidity, higher levels of adiponectin and membrane EPCR may represent a physiologic attempt to limit further endothelial damage, and the observed increase in plaque and progression of SLE nephritis represent an overwhelming of this reparative process by disease-provoking stimuli.

Cytokine overproduction, T-cell activation, and defective T-regulatory functions promote nephritis in systemic lupus erythematosus

Lupus nephritis (LN) occurs in more than one-third of patients with systemic lupus erythematosus. Its pathogenesis is mostly attributable to the glomerular deposition of immune complexes and overproduction of T helper- (Th-) 1 cytokines. In this context, the high glomerular expression of IL-12 and IL-18 exerts a major pathogenetic role. These cytokines are locally produced by both macrophages and dendritic cells (DCs) which attract other inflammatory cells leading to maintenance of the kidney inflammation. However, other populations including T-cells and B-cells are integral for the development and worsening of renal damage. T-cells include many pathogenetic subsets, and the activation of Th-17 in keeping with defective T-regulatory (Treg) cell function regards as further event contributing to the glomerular damage. These populations also activate B-cells to produce nephritogenic auto-antibodies. Thus, LN includes a complex pathogenetic mechanism that involves different players and the evaluation of their activity may provide an effective tool for monitoring the onset of the disease.

Trafficking properties of plasmacytoid dendritic cells in health and disease

Plasmacytoid dendritic cells (PDCs) represent a subset of circulating leukocytes characterized by the ability to release high levels of type I interferon (IFN). Under homeostatic conditions PDCs are confined to primary and secondary lymphoid organs. This is consistent with the restricted profile of functional chemotactic receptors expressed by circulating PDCs (i.e. CXCR4 and ChemR23). Accumulation of PDCs in non-lymphoid tissue is, however, observed in certain autoimmune diseases, allergic reactions and tumors. Indeed, PDCs are now considered to be involved in the pathogenesis of diseases characterized by a type I IFN-signature and are considered as a promising target for new intervention strategies. Here, current knowledge of the molecular mechanisms involved in the recruitment of PDCs under homeostatic and pathological conditions are summarized.

Oversecretion of cytokines and chemokines in lupus nephritis is regulated by intraparenchymal dendritic cells: a review

Lupus nephritis (LN) occurs in more than one-third of patients with systemic lupus erythematosus. Its pathogenesis is attributed to the glomerular deposition of immune complexes as well as to imbalance of the cytokine homeostasis. In this context, high production of cytokines and chemokines by dendritic cells (DCs) may concur to LN. In addition, urinary cytokine excretion may reflect the accumulation of DCs within glomeruli. DCs are differentiated in both myeloid and plasmacytoid (p) subsets in relation to their typical antigen and chemokine expression. Both subsets migrate in response to chemotactic stimuli because pDCs are susceptible to IL-18 expressed by resident glomerular cells. pDCs bear the IL-18R, and it is conceivable that DCs migrate to the kidney under the attraction of IL-18. Therefore, the depletion of DCs reflects the inflammation severity in LN, whereas measurement of Th1 cytokines may represent an effective tool for monitoring the onset of LN.

Primary infection with simian immunodeficiency virus: plasmacytoid dendritic cell homing to lymph nodes, type I interferon, and immune suppression

Plasmacytoid dendritic cells (pDCs) are antigen-presenting cells that develop into type-I interferon (IFN-I)-producing cells in response to pathogens. Their role in human immunodeficiency virus (HIV) pathogenesis needs to be understood. We analyzed their dynamics in relation to innate and adaptive immunity very early during the acute phase of simian immunodeficiency virus (SIV) infection in 18 macaques. pDC counts decreased in blood and increased in peripheral lymph nodes, consistent with early recruitment in secondary lymphoid tissues. These changes correlated with the kinetic and intensity of viremia and were associated with a peak of plasma IFN-I. IFN-I and viremia were positively correlated with functional activity of the immune suppression associated enzyme indoleamine-2,3-dioxygenase (IDO) and FoxP3(+)CD8(+) T cells, which both negatively correlated with SIV-specific T-cell proliferation and CD4(+) T-cell activation. These data suggest that pDCs and IFN-I play a key role in shaping innate and adaptive immunity toward suppressive pathways during the acute phase of SIV/HIV primary infection.

Plasma interleukin-18 and dendritic cells in males with psoriasis vulgaris

Peripheral blood dendritic cells seem to play a crucial role in psoriatic inflammatory processes. The aim of our study is to investigate the relationship between plasma interleukin-18 (IL-18) levels and blood dendritic cells in psoriatic patients. IL-18 plasma levels were measured by ELISA. Phenotypes of dendritic cell subsets were analyzed by double-colour flow cytometry. Plasma IL-18 level in psoriatic males was significantly higher, whereas counts of BDCA-2+ cells were lower than in the control group. The myeloid/plasmacytoid ratio was significantly higher in the patient group compared to the control one. In the patient group, significant negative correlations between plasma IL-18 level and both the BDCA-1+ and BDCA-2+ counts were found. BDCA-1+ counts correlated negatively with percentage of skin involvement. IL-18 seems to play a role in psoriasis pathogenesis. The decreased counts of blood plasmacytoid DCs in psoriatic patients might result from IL-18 down-regulation of plasmacytoid DC precursor proliferation.

Cytokines and anticytokines in psoriasis

BACKGROUND

Psoriasis is a chronic autoimmune hyperproliferative skin disease of varying severity affecting approximately 2-3% of the general population in the USA and Europe. Although the pathogenesis of psoriasis has not been fully elucidated, an immunologic-genetic relationship is likely. Cutaneous and systemic overexpression of various proinflammatory cytokines (TNF, interleukins, interferon-gamma) has been demonstrated in psoriatic patients.

METHODS

We reviewed the current database literature and summarized the involvement of cytokines and their receptors in the pathogenesis and treatment of psoriasis.

RESULTS

Although many cytokine/anti-cytokine therapies have been conducted, TNF antagonists in the treatment of both psoriasis arthropatica and vulgaris appear to be the most widely used clinically. Interestingly, the efficacy and tolerability of some cytokines (rhIL-11 or ABX-IL-8,) were found to be much lower than expected.

CONCLUSIONS

Preliminary results obtained with cytokine and anti-cytokine therapies appear promising and as such continued research is clearly indicated.

Rheumatoid arthritis synovium contains two subsets of CD83-DC-LAMP- dendritic cells with distinct cytokine profiles

Dendritic cells (DCs) have been proposed to play a pivotal role in the initiation and perpetuation of rheumatoid arthritis (RA) by presentation of arthritogenic antigens to T cells. We investigated the in vivo characteristics of two major DC subsets, myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), in RA synovial tissue (ST) by measuring their frequency, phenotype, distribution, and cytokine expression. ST was obtained by arthroscopy from 20 RA, 8 psoriatic arthritis, and 10 inflammatory osteoarthritis patients. Levels of CD1c(+) mDCs and CD304(+) pDCs present in ST were quantified by digital image analysis, and their distribution was assessed by double immunolabeling with antibodies against CD3 and CD8. The maturation status and cytokine profile of mDCs and pDCs were quantified by double-immunofluorescence microscopy. In RA patients, the number of CD304(+) pDCs exceeded that of CD1c(+) mDCs, with the majority of infiltrating DCs being CD83(-) or DC-LAMP(-). Synovial pDC numbers were especially increased in RA patients who were positive for rheumatoid factor and anti-citrullinated peptide antibody. mDCs and pDCs were localized adjacent to lymphocyte aggregates. In ST from RA patients, both mDCs and pDCs expressed interleukin (IL)-15. IL-18 and interferon (IFN)-alpha/beta were mainly expressed by pDCs whereas IL-12p70 and IL-23p19 expression was predominant in mDCs. These data characterize the phenotypes of mDCs and pDCs in inflammatory synovitis and define for the first time the cytokine expression profile of these DC subsets.

Increased IL-18 production by dendritic cells in active inflammatory myopathies

Inflammatory myopathies (IM) are chronic disorders characterized by muscular accumulation of inflammatory cells that promote cytotoxicity and tissue damage. Overexpression of chemokines and cytokines as well as imbalance of dendritic cells (DC) homeostasis have been postulated to exert a role in both dermatomyositis (DM) and polymyositis (PM). We studied the T helper (Th)-1 and Th2 cytokine levels by enzyme linked immunosorbent assay (ELISA) and the muscular expression of IL-18 and its receptor by both histochemistry (HIC) and in situ hybridization (ISH) in both patients and normal controls. Also, the cell populations infiltrating the muscles were investigated. We present evidence that DM and PM are characterized by a predominant Th1 immune response with high production of both interferon (IFN)-gamma and interleukin (IL)-18 in the presence of reduced levels of IL-4 and IL-6. IL-18 was also demonstrated in muscles and produced by both macrophages and DC surrounding either perivascular and perimysium areas or endomysium. IL-18R was highly expressed by T cells and DC as well as by endothelial cells (EC) and smooth muscle cells (SMC). High concentrations of serum and muscular IL-18 suggest that deregulated IL-18/IL-18R pathway may be pathogenetic in IM and measurement of IL-18 might be predictive of the disease activity.

NK cells at the interface between innate and adaptive immunity

In recent years a novel concept has emerged indicating that the actual role of natural killer (NK) cells is not confined to the destruction of virus-infected cells or tumors. Indeed, different NK subsets exist that display major functional differences in their cytolytic activity, cytokine production and homing capabilities. In particular, CD56(high) CD16(-) NK cells that largely predominate in lymph nodes, have little cytolytic activity but release high levels of cytokines whereas CD56(low) CD16(+) NK cells that predominate in peripheral blood and inflamed tissues, display lower cytokine production, but potent cytotoxicity. The latter is characterized by granule polarization and exocytosis of various proteins including perforin and granzymes that mediate target cell killing. The recruitment of CD56(low) CD16(+) NK cells into inflamed peripheral tissues is orchestrated by various chemochines including the newly identified Chemerin. At these sites, NK cells, upon engagement of different triggering receptors become activated and upregulate their cytokine production and cytotoxicity after interaction with myeloid dendritic cells (DCs). Importantly, during this interaction NK cells also mediate the 'editing' of DCs undergoing maturation. This process appears to play a crucial role in shaping both innate and adaptive immune responses. Indeed, only DCs undergoing this NK-mediated quality control would become fully mature and capable of inducing priming of protective Th1 responses.

Cellular targets of interleukin-18 in rheumatoid arthritis

Recent data are presented which indicate a critical role for interleukin (IL)-18 in rheumatoid arthritis (RA). The T cells and macrophages invading the synovium or in the synovial fluid are the chief cellular targets of IL-18 in RA. Neutrophils, dendritic cells and endothelial cells may also be cellular mediators of IL-18. The direct effect of IL-18 on fibroblast-like synoviocytes or chondrocytes may not be essential or important. In RA, IL-18, which is mainly produced by macrophages, activates T cells and macrophages to produce proinflammatory cytokines, chemokines, adhesion molecules and RANKL which, in turn, perpetuate chronic inflammation and induce bone and cartilage destruction.

Interleukin-18 and the pathogenesis of inflammatory diseases

Several autoimmune diseases are thought to be mediated in part by interleukin (IL)-18. Many are those with associated increased interferon-gamma (IFNgamma) levels such as systemic lupus erythematosus, macrophage activation syndrome, rheumatoid arthritis, Crohn's disease, psoriasis, and graft-versus-host disease. In addition, ischemia, including acute renal failure in human beings, appears to involve IL-18. Animal studies also support the concept that IL-18 is a key player in models of lupus erythematosus, atherosclerosis, graft-versus-host disease, and hepatitis. Unexpectedly, IL-18 plays a role in appetite control and the development of obesity. IL-18 is a member of the IL-1 family; IL-1beta and IL-18 are related closely, and both require the intracellular cysteine protease caspase-1 for biological activity. The IL-18 binding protein, a naturally occurring and specific inhibitor of IL-18, neutralizes IL-18 activities and has been shown to be safe in patients. Other options for reducing IL-18 activities are inhibitors of caspase-1, human monoclonal antibodies to IL-18, soluble IL-18 receptors, and anti-IL-18 receptor monoclonal antibodies.

Terminal complement complex C5b-9-treated human monocyte-derived dendritic cells undergo maturation and induce Th1 polarization

Sublytic C5b-9 has been described as a pro-inflammatory mediator that triggers cell activation rather than inducing cell death. Dendritic cells (DC) play a critical role in controlling antigen-specific immune responses. Although DC maturation induced by various stimuli has been well characterized, the role of C5b-9 in DC function has not been described. In this report, we use in vitro assembled functional C5b-9 based on purified distal complement protein to show that DC maturation is promoted by sublytic C5b-9. This was demonstrated by up-regulation of CD83, HLA-antigens and costimulatory molecules, including CD80, D86, B7-H1, B7-H3, B7-H4 and BTLA. In addition, secretion of cytokines such as interleukin (IL)-12 and tumor necrosis factor-alpha was increased while the capacity for antigen uptake (FITC-Dextran and Lucifer Yellow) was reduced in C5b-9-treated DC. Mixed lymphocyte reactions indicated that C5b-9-activated DC acted as stimulators that significantly promoted CD4+ T cell activation and elicited production of cytokines, including interferon-gamma and IL-2. Interestingly, C5b-9-treated DC also orient CD4+ CD45RA+ naïve T cells toward Th1 polarization. Our results are the first to report that DC are potential immunoregulatory targets of C5b-9, suggesting that C5b-9 bridges innate and acquired immunity by inducing DC maturation.

Intradermal vaccination of MUC1 transgenic mice with MUC1/IL-18 plasmid DNA suppresses experimental pulmonary metastases

MUC1 (mucin 1) is a transmembrane glycoprotein normally expressed on epithelia of the pancreas, breast, prostate, colon, and lung. However, this self-antigen is over-expressed and aberrantly glycosylated in adenocarcinomas, thereby making it a potential target for immunotherapy. Toward this goal, DNA plasmids encoding human MUC1 (pMUC1) and mouse interleukin-18 (pmuIL-18) were developed, and previous work demonstrated pMUC1/pmuIL18 vaccination protected MUC1 transgenic mice (MUC1.Tg) from subcutaneous tumor challenge. This report shows that pMUC1/pmuIL-18 is effective in preventing and treating pulmonary metastases in MUC1.Tg mice. Vaccination with pMUC1 or pmuIL-18 alone was insufficient to elicit measurable anti-tumor effects. However, co-administration of pMUC1 with pmuIL-18 reduced the incidence of lung tumors and prolonged survival. Furthermore, pMUC1/pmuIL-18 immunization protected mice from challenge with MUC1+ tumors, but not from MUC1- tumors, indicating that the anti-tumor effect is antigen-specific. More importantly, pMUC1/pmuIL-18 was effective in treating established tumors. Finally, in vivo antibody-mediated lymphocyte depletion and neutralization of interferon gamma (IFNgamma) revealed that CD8+ T cells and IFNgamma mediate the anti-tumor immunity. Collectively, these results demonstrate that pMUC1/pmuIL-18 breaks tolerance to MUC1, and induces antigen-specific immunity with protective and therapeutic benefit. This suggests that pMUC1/pmuIL-18 DNA vaccination may provide clinical benefit for patients with MUC1+ tumors.

Effector and regulatory events during natural killer-dendritic cell interactions

The different cell types of the innate immune system can interact with each other and influence the quality and strength of an immune response. The cross talk between natural killer (NK) cells and myeloid dendritic cells (DCs) leads to NK cell activation and DC maturation. Activated NK cells are capable of killing DCs that fail to undergo proper maturation ('DC editing'). Encounters between NK cells and DCs occur in both inflamed peripheral tissues and lymph nodes, where both cell types are recruited by chemokines released in the early phases of inflammatory responses. Different NK cell subsets (CD56(bright)CD16(-) versus CD56(+)CD16(+)) differ in their homing capabilities. In particular, CD56(bright)CD16(-) NK cells largely predominate the lymph nodes. In addition, these two subsets display major functional differences in their cytolytic activity, cytokine production, and ability to undergo proliferation. NK cell functions are also greatly influenced by the presence of polarizing cytokines such as interleukin (IL)-12 and IL-4. The cytokine microenvironment reflects the presence of different cell types that secrete such cytokines in response to microbial products acting on different Toll-like receptors (TLRs). Moreover, NK cells themselves can respond directly to microbial products by means of TLR3 and TLR9. Thus, it appears that the final outcome of a response to microbial infection may greatly vary as a result of the interactions occurring between different pathogen-derived products and different cell types of the innate immunity system. These interactions also determine the quality and strength of the subsequent adaptive responses. Remarkably, NK cells appear to play a key role in this complex network.

Interleukin-18 overexpression as a hallmark of the activity of autoimmune inflammatory myopathies

The objective of this study was to explore the role of interleukin (IL)-18 in patients with inflammatory myopathies (IM) such as dermatomyositis (DM) and polymyositis (PM) in relation to the possible predominance of a Th1 immune response in their pathogenesis. Serum concentrations of IL-18, interferon (IFN)-gamma, IL-4 and IL-6 were measured in six patients by enzyme-linked immunosorbent assay (ELISA). IL-18 expression was evaluated by in situ hybridization (ISH), whereas CD68, CD8 and CD83 were investigated by immunohistochemistry (IHC) to define the main producers of IL-18. Lastly, the expression of both IL-18 receptor (IL-18R) and monocyte chemoattractant protein (MCP)-1 was also explored by IHC. High serum levels of IL-18 and IFN-gamma, and conversely low titres of IL-4 and IL-6, were demonstrated in both diseases. In addition, IL-18 was overexpressed in muscle biopsy specimens from patients with IM. Both macrophages and dendritic cells (DC) surrounding either perivascular and perimysium areas in DM or endomysium in PM were the main producers of IL-18. Endothelial cells (EC), smooth muscle cells (SMC) and CD8(+) T cells expressed a high content of IL-18R. Vessel cells overexpressed MCP-1 in parallel with IL-18R. High concentrations of serum IL-18 as well as muscular up-regulation of IL-18 and IL-18R suggest that deregulation of the IL-18/IL-18R pathway is a pathogenetic mechanism in IM. Measurement of IL-18 may thus predict the severity of both DM and PM.

Interleukin 18-independent engagement of interleukin 18 receptor-alpha is required for autoimmune inflammation

T helper type 1 (T(H)1) lymphocytes are considered to be the main pathogenic cell type responsible for organ-specific autoimmune inflammation. As interleukin 18 (IL-18) is a cofactor with IL-12 in promoting T(H)1 cell development, we examined the function of IL-18 and its receptor, IL-18R, in autoimmune central nervous system inflammation. Similar to IL-12-deficient mice, IL-18-deficient mice were susceptible to experimental autoimmune encephalomyelitis. In contrast, IL-18R alpha-deficient mice were resistant to experimental autoimmune encephalomyelitis, indicating involvement of an IL-18R alpha ligand other than IL-18 with encephalitogenic properties. Moreover, engagement of IL-18R alpha on antigen-presenting cells was required for the generation of pathogenic IL-17-producing T helper cells. Thus, IL-18 and T(H)1 cells are dispensable, whereas IL-18R alpha and IL-17-producing T helper cells are required, for autoimmune central nervous system inflammation.

Role of regulatory dendritic cells in allergy and asthma

PURPOSE OF REVIEW

Dendritic cells are the most efficient inducers of all immune responses, and are capable of inducing either productive immunity or maintaining the state of tolerance to self-antigens and allergens. The present review summarizes the emerging literature on dendritic cells, with the emphasis on regulatory function of dendritic cells in allergy and asthma. In particular we summarize recent data regarding the relationship between dendritic cell subsets and Th1, Th2 and regulatory T (TReg) cells.

RECENT FINDINGS

The diverse functions of dendritic cells have been attributed to distinct lineages of dendritic cells, which arise from common immature precursor cells that differentiate in response to specific maturation-inducing or local microenvironment conditions. These subsets induce different lineages of T cells such as Th1, Th2 and TReg cells, including Th1Reg and Th2Reg cells, which regulate allergic diseases and asthma.

SUMMARY

Subsets of dendritic cells regulate the induction of a variety of T-cell subtypes, which suppress the development of allergy and asthma, thus providing antiinflammatory responses and protective immunity.

The interplay of chemokines and dendritic cells in the pathogenesis of lupus nephritis

Lupus nephritis (LN) occurs in more that one-third of patients with systemic lupus erythematosus. Production of nephritogenic autoantibodies, glomerular immune complex deposition, and cytokine overproduction have been postulated to contribute to the pathogenesis of LN. However, overexpression of chemokines and imbalance of dendritic cell (DC) homeostasis may contribute to the development of nephritis in SLE. We present evidence that monocyte chemoattractant protein (MCP)-1 promotes renal disease in experimental glomerulonephritis, while its increased urinary levels reflect the severity of the disease in humans. Although macrophages are the prevalent infiltrating population within the kidney, it has been recently proposed that several chemokines and related receptors expressed by DCs may divide this cell population into myeloid (mDC) and plasmacytoid (pDC) subsets. However, the chemokine receptors expressed by pDCs are not functional, and other molecules are involved in the chemoattraction of these cells. We found increased expression of interleukin (IL)-18 in glomeruli of patients with active LN along with glomerular infiltration by pDCS. Since pDCs bear IL-18 receptor (IL-18R), it is conceivable that circulating pDCs may migrate toward glomeruli by IL-18/IL-18R interactions. Therefore, the relative depletion of circulating pDCs reflects the severity of inflammatory disease in LN.

Interleukins 18 and 21: biology, mechanisms of action, toxicity, and clinical activity

Interleukins 18 and 21 have been described, and the effect of each upon immune response and experimental tumors in animals has been the subject of much recent work. Both interleukins have shown antitumor effects in animals, which in some models are striking for their duration, specificity, and ability to protect against rechallenge with the same tumor. These characteristics suggest immunologic involvement in the antitumor response, and several papers suggest involvement of both innate and adaptive immune mechanisms. Recent early phase I clinical trials in human cancer patients have demonstrated evidence of clinical response. This review discusses the biology, preclinical animal tumor model data, and early clinical trial findings.

Interleukin-18: a novel prognostic cytokine in bacteria-induced sepsis

OBJECTIVE

Severe inflammation and sepsis remain a serious clinical challenge worldwide. Despite modern supportive medicine and an improved understanding of the underlying pathophysiology, mortality rates remain high in patients suffering from this severe inflammatory process. The often excess production of pro- and anti-inflammatory cytokines frequently found in the circulation of septic patients has stimulated the search for reliable inflammatory mediators that can be used for the diagnosis and prediction of clinical outcome. Interleukin (IL)-18, formerly termed interferon-gamma inducing factor, is a pro-inflammatory and Th1 cytokine suggested to play a significant role in the pathogenesis of this disease. This review focuses on our current understanding of the pro-inflammatory cytokine, IL-18, and its potentially unique role in sepsis.

METHODS

Bibliographic search of the most recent literature (1995-2005) relating to IL-18 and its role in inflammatory diseases, with emphasis on its pathophysiological importance in sepsis. In addition, a summary of the author's own experimental data from this particular field of research set in the context of current knowledge regarding IL-18.

RESULTS AND CONCLUSIONS

Several studies have shown elevated plasma IL-18 concentrations to be associated with poor clinical outcome in severe inflammatory and septic conditions. Moreover, a significant increase in IL-18 concentrations has been shown to discriminate between Gram-positive and Gram-negative related sepsis, and, thus, may potentially augment existing diagnostic tools. Biological neutralization of IL-18 via caspase-1 intervention or through the administration of IL-18-binding protein has been promulgated as a promising therapeutic approach, but additional studies are required to evaluate its full potential in acute inflammatory diseases.

IL-12p70 and IL-18 gene-modified dendritic cells loaded with tumor antigen-derived peptides or recombinant protein effectively stimulate specific Type-1 CD4+ T-cell responses from normal donors and melanoma patients in vitro

Although CD4(+) Type-1T helper (Th1) cells secreting interferon-gamma (IFN-gamma) appear to play an essential role in promoting durable antitumor immunity, we have previously shown that patients with cancer exhibit dysfunctional Th1-type responses against epitopes derived from tumor antigens, such as MAGE-A6. Here, we engineered human dendritic cells (DCs) to secrete high levels of the IFN-gamma-inducing cytokines, interleukin (IL)-12p70 and IL-18, via recombinant adenoviral infection to generate an in vitro stimulus capable of promoting previously deficient patient Th1-type responses. Dendritic cells co-infected with Ad.IL-12 and Ad.IL-18 (DC.IL-12/18) were more effective at stimulating MAGE-A6-specific Th1-type CD4(+) T-cell responses than DCs infected with either of the cytokine vectors alone, control Ad.Psi5 virus or uninfected DCs. Furthermore, we show that DC.IL-12/18 loaded with recombinant MAGE-A6 protein (rMAGE) and used as in vitro stimulators promote Th1-type immunity that is frequently directed against multiple MAGE-A6-derived epitopes. The superiority of DC.IL-12/18-based stimulations in melanoma patients was independent of disease stage or current disease status. Based on these results, we believe this modality may prove clinically useful as a vaccine platform to promote the recovery of tumor antigen-specific, Th1-type CD4(+) T-cell responses in patients with cancer.

Interleukin 1 and interleukin 18 as mediators of inflammation and the aging process

In this review, 2 cytokines are discussed with respect to the inflammatory processes that are fundamental to aging and mortality. Both interleukin (IL)-1 and IL-18 are members of the same structural family (IL-1 family, or IL-F); there are presently 9 members of this family, but with the exception of IL-1alpha, IL-1beta, and IL-18, the others are antagonists or remain without known function. IL-1alpha is an intracellular cytokine with properties of both a cytokine and a transcription factor. IL-1beta and IL-18 are closely related; both possess a similar three-dimensional structure, and their respective precursor forms are inactive until cleaved by the intracellular cysteine protease caspase-1. Patients with mutations in the NALP3 gene, which controls the activity of caspase-1, readily secrete more IL-1beta and IL-18 and suffer from systemic inflammatory diseases. Patients with defects in this gene have high circulating concentrations of IL-6, serum amyloid A, and C-reactive protein, each of which decrease rapidly upon blockade of the IL-1 receptor, which suggests that IL-1beta contributes to the elevation of these markers of the inflammatory mechanisms of aging. Animal studies support the concept that IL-1beta and IL-18 participate in the pathogenesis of atherosclerosis. For example, overexpression of the IL-18 binding protein, a naturally occurring, specific inhibitor of IL-18, prevents the spontaneous development of atherosclerosis in apolipoprotein E-deficient mice. From human and animal studies, one may conclude that IL-1beta and IL-18 participate in fundamental inflammatory processes that increase during the aging process.

Primary alloproliferative TH1 response induced by immature plasmacytoid dendritic cells in collaboration with myeloid DCs

The role played by dendritic cell (DC) subsets in the immune response to alloantigens is not well defined. In vitro experiments have extensively shown that freshly isolated myeloid (M)DCs induce a strong T lymphocyte proliferation whereas plasmacytoid (P)DCs do not, unless activated by CD40 ligation. The aim of these studies was to explore whether the interplay among PDCs, MDCs and T cells modulates alloresponse. Freshly isolated MDCs and PDCs were merged in different proportions and used as antigen presenting cells (APCs) in mixed lymphocyte cultures (MLC). As described, isolated PDCs only induced a mild alloresponse, while MDCs were potent inducers of alloproliferation. Unexpectedly, when PDCs were merged with even low numbers of MDCs (down to 100 cells) and used as APCs, a potent Th1 cell proliferation was detected. Survival and maturation of PDCs was increased in these MLC conditions, which could partially explain the magnitude of the T-cell response. Interestingly, the proportion of IFNgamma-producing cells generated in such cultures was higher compared to MDC-stimulated cultures. These data suggest that the interaction between both DC subsets is determinant to generate a potent Th1 response, at least in an allogeneic situation, and may be relevant to the outcome of allogeneic stem cell transplantation.

Dendritic cell trafficking: More than just chemokines

Dendritic cells (DC) are professional antigen presenting cells. To accomplish their biological function they need to undergo a complex pattern of migration which includes their localization to both peripheral non-lymphoid tissues and secondary lymphoid organs. In the absence of correct tissue localization, DC fail to promote proper immune responses. The first description of chemotactic factors active on DC was published by this group 10 years ago. Since then, it was described that multiple signals are able to regulate the migration of DC in vitro and in vivo. These signals include nonchemokine chemotactic agonists, lipid mediators and membrane proteins. This review summarizes this large body of information and focuses on the complexity of the process of DC trafficking.

Th1 cytokines in the pathogenesis of lupus nephritis: The role of IL-18

Excessive T helper cell function is a hallmark of systemic lupus erythematosus and abnormalities of T helper cytokine profiles have been implicated in loss of immune tolerance, increased antigenic load, defective B cell suppression and a variety of clinical manifestations. Here, we emphasize the importance of T helper 1-type (i.e., IFN-gamma) with respect to T helper 2-type (i.e., IL-4) cytokines in promoting the pathogenesis of lupus nephritis focusing on the critical role of IL-18, a major T helper 1 differentiation factor. IL-18 is overexpressed in patients with lupus nephritis along with higher INF-gammaand lower IL-4 production as compared to non-nephritic lupus patients. We hypothesize a pathogenic model where both the onset and aggravation of nephritis are promoted by an imbalance of immune response towards a T helper 1 cytokine predominance due to IL-18 up-regulation. In contrast, a T helper 2-skewed cytokine profile may possibly prevent the development of renal disease. In this context, IL-18 represents a novel marker of lupus nephritis and its measurement may be helpful in the assessment of patients.

Gene Family Clustering Identifies Functionally Associated Subsets of Human In Vivo Blood and Tonsillar Dendritic Cells

Human dendritic cells (DCs) are a distinct but heterogeneous lineage of APCs operating as the link between innate and adaptive immune responses, with the function to either maintain tolerance or trigger immunity. The DC lineage consists of several subpopulations with unique phenotypes; however, their functional characteristics and transcriptional similarities remain largely unknown. To further characterize the phenotypes and transcriptomes of the subsets, we purified myeloid CD16(+), blood DC Ag 1(+) (BDCA1(+)), and BDCA3(+) DC populations, as well as plasmacytoid CD123(+) DCs, from tonsillar tissue and peripheral blood. Transcriptional profiling and hierarchical clustering visualized that BDCA1(+) DCs clustered with BDCA3(+) DCs, whereas CD16(+) DCs and CD123(+) DCs clustered as distinct populations in blood. Differential expression levels of chemokines, ILs, and pattern recognition receptors were demonstrated, which emphasize innate DC subset specialization. Even though highly BDCA1(+) and BDCA3(+) DC-specific gene expression was identified in blood, the BDCA1(+) DCs and BDCA3(+) DCs from tonsils displayed similar transcriptional activity, most likely due to the pathogenic or inflammatory maturational signals present in tonsillar tissues. Of note, plasmacytoid DCs displayed less plasticity in their transcriptional activity compared with myeloid DCs. The data demonstrated a functionally distinct association of each of the seven subsets based on their signatures, involving regulatory genes in adaptive and innate immunity.