Accessory cell-derived interleukin-12 and prostaglandin E2 determine the level of interferon-gamma produced by activated human CD4+ T cells

Eicosanoid Control Over Antigen Presenting Cells in Asthma

Asthma is a common lung disease affecting 300 million people worldwide. Allergic asthma is recognized as a prototypical Th2 disorder, orchestrated by an aberrant adaptive CD4+ T helper (Th2/Th17) cell immune response against airborne allergens, that leads to eosinophilic inflammation, reversible bronchoconstriction, and mucus overproduction. Other forms of asthma are controlled by an eosinophil-rich innate ILC2 response driven by epithelial damage, whereas in some patients with more neutrophilia, the disease is driven by Th17 cells. Dendritic cells (DCs) and macrophages are crucial regulators of type 2 immunity in asthma. Numerous lipid mediators including the eicosanoids prostaglandins and leukotrienes influence key functions of these cells, leading to either pro- or anti-inflammatory effects on disease outcome. In this review, we will discuss how eicosanoids affect the functions of DCs and macrophages in the asthmatic lung and how this leads to aberrant T cell differentiation that causes disease.

Anti-inflammation therapy by activation of prostaglandin EP4 receptor in cardiovascular and other inflammatory diseases

Prostaglandin E2 constitutes a major cyclooxygenase-2-derived prostanoid produced at inflammatory sites. In vitro and in vivo data support its role as a modulator of inflammation. Prostaglandin E2 exerts anti-inflammatory effects by binding to one of its receptors, the prostaglandin E receptor 4 (EP4), thereby modulating macrophage and T lymphocyte functions that participate crucially in innate and adaptive immunity and tissue remodeling and repair. The activation of EP4 suppresses the release of cytokines and chemokines from macrophages and T cells, inhibits the proliferation and the activation of T cells, and induces T-cell apoptosis. Lack of EP4 in bone marrow-derived cells accelerates local inflammation in atherosclerotic and aneurysm lesions and increases the prevalence of aneurysm formation. An EP4 agonist promotes graft survival in allograft cardiac transplantation and dampens tissue damage after myocardial ischemia. Anti-inflammatory actions of EP4 agonism may benefit other inflammatory disorders, including colitis and gastric ulcers. By contrast, EP4 acts as a proinflammatory mediator in encephalomyelitis, skin inflammation, and arthritis by promoting T helper (Th) 1 differentiation and Th17 expansion. Overall, EP4 activation produces powerful anti-inflammatory responses in many experimental diseases, rendering EP4 agonists attractive agents to attenuate syndromes associated with inflammation.

Role of dendritic cells: a step forward for the hygiene hypothesis

The hygiene hypothesis was proposed more than two decades ago, but its mechanism remains unclear. This review focuses on recent advances in the field, especially on the role played by dendritic cells (DCs) and their modulating effects on various infections and allergic diseases, including allergic asthma. DCs isolated from mice long after the resolution of an infection were reported to have a significant modulating effect on allergen-specific Th2 responses in both in vitro and in vivo systems. These DCs showed DC1-like and/or tolerogenic DC capacity, which allowed for the inhibition of allergic responses by immune deviation (enhancing Th1 response) and immune regulation (through regulatory T-cell and Th2 hyporesponsiveness) mechanisms. These findings represented a significant advance in the elucidation of the mechanisms underlying the hygiene hypothesis. Further investigation on the mechanisms by which DCs are 'educated' by infectious agents and the influence of the type, time, and extent of infections on this 'education' process will help us understand immune regulation in disease settings and in the rational design of preventive/therapeutic approaches to allergy/asthma and infections.

Deletion of EP4 on bone marrow-derived cells enhances inflammation and angiotensin II-induced abdominal aortic aneurysm formation

OBJECTIVE

To examine whether a lack of prostaglandin E receptor 4 (EP4) on bone marrow-derived cells would increase local inflammation and enhance the formation of abdominal aortic aneurysm (AAA) in vivo.

METHODS AND RESULTS

Prostaglandin E(2) (PGE(2)) through activation of EP4, can mute inflammation. Hypercholesterolemic low-density lipoprotein receptor knockout (LDLR(-/-)) mice transplanted with either EP4(+/+) (EP4(+/+)/LDLR(-/-)) or EP4(-/-) (EP4(-/-)/LDLR(-/-)) bone marrow received infusions of angiotensin II to induce AAA. Deficiency of EP4 on bone marrow-derived cells increased the incidence (50% of male EP4(+/+)/LDLR(-/-) mice versus 88.9% of male EP4(-/-)/LDLR(-/-) mice developed AAA; and 22% of female EP4(+/+)/LDLR(-/-) mice versus 83.3% of female EP4(-/-)/LDLR(-/-) mice developed AAA) and severity of AAA, increased monocyte chemoattractant protein-1 (2.72-fold in males and 1.64-fold in females), and enhanced infiltration of macrophages (3.8-fold in males and 2.44-fold in females) and T cells (1.88-fold in males and 1.66-fold in females) into AAA lesions. Lack of EP4 on bone marrow-derived cells augmented elastin fragmentation, increased apoptotic markers, and decreased smooth muscle cell accumulation within AAA lesions.

CONCLUSIONS

Deficiency of EP4 on bone marrow-derived cells boosted inflammation and AAA formation induced by angiotensin II in hyperlipidemic mice. This study affirms the pathophysiologic importance of PGE(2) signaling through EP4 as an endogenous anti-inflammatory pathway involved in experimental aneurysm formation.

Expression of cyclooxygenase-1 and cyclooxygenase-2 in human renal allograft rejection - a prospective study

Cyclooxygenases (COX) are known to be involved in inflammatory kidney diseases. However, there are no data available about the expression of COX-1 and only preliminary reports about the expression of COX-2 in biopsies of patients undergoing acute renal allograft rejection. We conducted this prospective study to analyze the expression, distribution, and cellular localization of COX-1 and -2 and thus to elucidate the role of COX in human kidney transplantation. One hundred forty-four biopsies were included from patients without rejection and unaltered morphology (n = 60), with acute interstitial rejection (n = 7), with acute vascular rejection (n = 21), with chronic allograft nephropathy (n = 16), without rejection but with various other lesions (n = 40). COX-1 and -2 expression was localized in each biopsy by immunohistochemistry. We found a highly significant up-regulation of COX-1 in vessels and in infiltrating interstitial cells of patients with acute allograft rejection compared with biopsies with well-preserved tissue. Also, COX-2 expression was significantly elevated in infiltrating interstitial cells of biopsies with acute rejection. This is the first prospective study demonstrating a significant induction of both COX-1 and -2 in human allograft biopsies with acute rejection after renal transplantation.

A novel prostaglandin E receptor 4-associated protein participates in antiinflammatory signaling

Prostaglandin E2 exerts an antiinflammatory action by ligation of the heptahelical receptor EP4 in human macrophages. Because the mechanism by which EP4 receptor stimulation suppresses inflammatory activation in macrophages remains undefined, we sought interactors with the carboxyl-terminal cytoplasmic domain of the EP4 receptor. Yeast 2-hybrid screening of the human bone marrow cDNA library with the EP4 receptor as a bait identified a cDNA clone encoding a 669-amino acid protein, designated here as EP4 receptor-associated protein (EPRAP), which contains 8 ankyrin motifs that might recruit other signaling molecules. EPRAP bound to the full-length EP4 receptor in HEK293 cells cotransfected with V5-tagged EPRAP and FLAG-tagged EP4 receptor cDNA, as anti-FLAG antibody coimmunoprecipitated EPRAP with the EP4 receptor from the lysates of cotransfected cells. Human macrophages derived from peripheral blood monocytes expressed an approximately 70-kDa protein detected by Western blotting with a polyclonal anti-EPRAP antibody. Fluorescence immunohistochemistry colocalized EPRAP with the EP4 receptor in human atheromata. Interference with EPRAP function by small interference RNA limited prostaglandin E2-mediated suppression of chemokine expression in macrophages activated with lipopolysaccharide and tumor necrosis factor alpha. In conclusion, the antiinflammatory action of prostaglandin E2 in macrophages involves EPRAP that associates directly with the cytoplasmic tail of EP4 receptor.

Contrasting Effects of Cyclooxygenase-1 (COX-1) and COX-2 Deficiency on the Host Response to Influenza A Viral Infection

Influenza is a significant cause of morbidity and mortality worldwide despite extensive research and vaccine availability. The cyclooxygenase (COX) pathway is important in modulating immune responses and is also a major target of nonsteroidal anti-inflammatory drugs (NSAIDs) and the newer COX-2 inhibitors. The purpose of the present study was to examine the effect of deficiency of COX-1 or COX-2 on the host response to influenza. We used an influenza A viral infection model in wild type (WT), COX-1-/-, and COX-2-/- mice. Infection induced less severe illness in COX-2-/- mice in comparison to WT and COX-1-/- mice as evidenced by body weight and body temperature changes. Mortality was significantly reduced in COX-2-/- mice. COX-1-/- mice had enhanced inflammation and earlier appearance of proinflammatory cytokines in the BAL fluid, whereas the inflammatory and cytokine responses were blunted in COX-2-/- mice. However, lung viral titers were markedly elevated in COX-2-/- mice relative to WT and COX-1-/- mice on day 4 of infection. Levels of PGE2 were reduced in COX-1-/- airways whereas cysteinyl leukotrienes were elevated in COX-2-/- airways following infection. Thus, deficiency of COX-1 and COX-2 leads to contrasting effects in the host response to influenza infection, and these differences are associated with altered production of prostaglandins and leukotrienes following infection. COX-1 deficiency is detrimental whereas COX-2 deficiency is beneficial to the host during influenza viral infection.

Increased release of IL-12p70 by monocytes after periodontal therapy

OBJECTIVES

It has been suggested that periodontal inflammation may result in an altered immune response. The peripheral immune capacity in periodontitis patients can be investigated using lipopolysaccharide (LPS)-stimulated whole blood cell cultures (WBCC), known to reflect the behavior of monocytes in particular. A previous study in our laboratory revealed that monocytes in the stimulated cultures from periodontitis patients behaved functionally different compared with controls. The present study investigated whether this different response of periodontitis patients' monocytes is intrinsic or acquired.

MATERIAL AND METHODS

The release of inflammatory mediators was measured in Escherichia coli LPS-stimulated WBCC from 12 periodontitis patients before and after periodontal therapy. In addition, the total leukocyte and leukocyte differentiation counts were also determined in the patients before and after therapy.

RESULTS

The levels of interleukin (IL)-12p70 in cell culture supernatants increased two times and those of prostaglandin E2 showed a trend towards reduction after therapy, whereas the levels of IL-1beta, IL-6, IL-8, IL-10, IL-12p40 and tumor necrosis factor-alpha did not change. The total number of white blood cells was decreased after periodontal therapy.

CONCLUSIONS

After periodontal therapy, the functional phenotype of the peripheral blood monocytes from patients was reconstituted, resembling that of subjects without periodontitis.

Renal cell carcinoma induces prostaglandin E2 and T-helper type 2 cytokine production in peripheral blood mononuclear cells

BACKGROUND

Patients with renal cell carcinoma (RCC) do not develop an effective antitumor immune response, despite significant infiltration by lymphocytes. Tumor production of immunosuppressive factors may account for this failure. The object of this study was to investigate the production of immunosuppressive mediators, especially prostaglandin E(2) (PGE(2)), by RCC.

METHODS

Peripheral blood mononuclear cells (PBMC) were cocultured with conditioned medium (CM) from human RCC cell lines in the presence or absence of NS-398, a selective cyclooxygenase 2 (COX-2) inhibitor. Supernatants were analyzed for levels of PGE(2), interleukin (IL)-10, IL-6, IL-2, interferon-gamma, and IL-12. The effects of RCC CM on PBMC proliferation were also examined. The expression of basal and stimulated COX-2 messenger RNA in the cell lines was assessed by reverse transcriptase-polymerase chain reaction.

RESULTS

RCC CM significantly increased PGE(2) production by PBMC. T-helper type 2 (Th2) cytokine production was also significantly increased. Th1 cytokines were unchanged or decreased. RCC CM increased proliferation of PBMC. Coculture with NS-398 reduced PBMC PGE(2) production to below control levels and significantly decreased IL-6 production and PBMC proliferation. NS-398 had no effect on cellular production of IL-10 or Th1 cytokines.

CONCLUSIONS

Human RCC inhibits the host antitumor immune response by promoting PGE(2) production and Th2 cytokines in PBMC. Selective inhibition of COX-2 may have a role in abrogating this effect.

Prostaglandin E2 suppresses chemokine production in human macrophages through the EP4 receptor

Pro-inflammatory pathways participate in the pathogenesis of atherosclerosis. However, the role of endogenous anti-inflammatory pathways in atheroma has received much less attention. Therefore, using cDNA microarrays, we screened for genes regulated by prostaglandin E(2) (PGE(2)), a potential endogenous anti-inflammatory mediator, in lipopolysaccharide (LPS)-treated human macrophages (MPhi). PGE(2) (50 nm) attenuated LPS-induced mRNA and protein expression of chemokines including monocyte chemoattractant protein-1, interleukin-8, macrophage inflammatory protein-1alpha and -1beta, and interferon-inducible protein-10. PGE(2) also inhibited the tumor necrosis factor-alpha-, interferon-gamma-, and interleukin-1beta-mediated expression of these chemokines. In contrast to the case of MPhi, PGE(2) did not suppress chemokine expression in human endothelial and smooth muscle cells (SMC) treated with LPS and pro-inflammatory cytokines. To assess the potential paracrine effect of endogenous PGE(2) on macrophage-derived chemokine production, we co-cultured MPhi with SMC in the presence of LPS. In these co-cultures, cyclooxygenase-2-dependent PGE(2) production exceeded that in the mono-cultures, and MIP-1beta declined significantly compared with MPhi cultured without SMC. We further documented prominent expression of the PGE(2) receptor EP4 in MPhi in both culture and human atheroma. Moreover, a selective EP4 antagonist completely reversed PGE(2)-mediated suppression of chemokine production. Thus, endogenous PGE(2) may modulate inflammation during atherogenesis and other inflammatory diseases by suppressing macrophage-derived chemokine production via the EP4 receptor.

Cyclooxygenases and prostaglandins: shaping up the immune response

The relevance of cyclooxygenases (COX)-1 and -2 and their products to inflammation, thrombosis and gastroprotection are well known. Their importance in the immune response was first recognized more than 25 years ago, but has only gained widespread attention recently. In this review, we attempt to integrate information on prostanoids and both the innate and acquired immune responses, including effects on leukocytes, antigen presenting cells, dendritic cells, T and B lymphocytes. Prostanoids may be relevant to immunotolerance, autoimmune disorders, transplantation, immunologic defense against tumors, acquired immunodeficiencies and viral infections. Insight into the role of prostanoids in immune function may afford novel therapeutic opportunities.

A type 2 response in lipopolysaccharide (LPS)-stimulated whole blood cell cultures from periodontitis patients

It is acknowledged that periodontitis results from the interaction of the host immune response with bacteria accumulating on the tooth surfaces. Although bacteria are essential, they are insufficient to cause the disease. Despite this knowledge it remains unclear why certain individuals are more susceptible to periodontitis than others. Therefore the present study investigated whether differences exist in the actual immune response between periodontitis patients and controls after stimulation of peripheral blood cells. Whole blood cell cultures (WBCC) were stimulated with LPS from Escherichia coli during 18 h and the release of prostaglandin E2 (PGE2), IL-1beta, IL-6, IL-8, IL-10, IL-12p40, IL-12p70 and tumour necrosis factor-alpha (TNF-alpha) was measured. The levels of PGE2 were two-fold higher in the WBCC from periodontitis patients than from controls. In contrast, the levels of IL-12p70 in WBCC from patients were two-fold lower. Furthermore, WBCC from patients secreted lower levels of IL-1beta and higher levels of IL-8 when compared with WBCC from controls. No differences were observed with respect to IL-6, IL-10, IL-12p40 and TNF-alpha production. It is known from the literature that LPS-stimulated WBCC reflect specifically the behaviour of the monocytes and that monocytes are peripheral precursors of antigen-presenting cells (APC). Therefore it is concluded that the monocytes in the present WBCC from periodontitis patients are responsible for the higher levels of PGE2 and lower levels of IL-12p70. Since it is has been shown that APC-derived IL-12p70 induces type (Th1) cells that promote cellular immunity, while APC-derived PGE2 induces type 2-helper (Th2) cells that promote humoral immunity, it is postulated that APC from periodontitis patients may have a bias in directing Th2 responses and thereby promoting the humoral immunity in periodontitis.

UVB irradiation modulates systemic immune responses by affecting cytokine production of antigen-presenting cells

The immunosuppressive effects of UVB irradiation have been well documented. The production of cytokines by keratinocytes is considered to play a major role in the induction of local as well as systemic immunosuppression. It is thought that partly due to the interaction of locally produced cytokines with antigen-presenting cells (APC) systemic effects, like antigen-specific tolerance, can be induced. In this study we examined the effect of UVB irradiation on cytokine profiles of peripheral APC as well as the functional consequences. Our results indicate that UVB irradiation impairs T(h)1-mediated immune responses in vivo by suppression of the systemic IL-12p70 production. Splenic APC from UVB-exposed mice showed an enhanced production of prostaglandin E(2), IL-1, IL-6 and tumor necrosis factor-alpha after in vitro stimulation. Also, spleen cells from UVB irradiated IL-4(-/-) mice showed increased IL-6 levels. These APC were less efficient in inducing IFN-gamma production by CD4(+) T cells and suppressed IgM production by B cells. We conclude that the altered cytokine profile of peripheral APC can be responsible for the systemic effects of UVB irradiation on the T(h)1/T(h)2 balance as well as on B cell responses.

Autoregulation of human monocyte-derived dendritic cell maturation and IL-12 production by cyclooxygenase-2-mediated prostanoid production

PG added to cell culture profoundly affect the in vitro maturation and function of monocyte-derived dendritic cells (MDC). Because unstimulated monocytes express cyclooxygenase (COX)-1, and COX-2 when activated, we examined whether MDC express these enzymes and produce prostanoids that autoregulate maturation and IL-12 production. Immature MDC (I-MDC) and mature MDC express COX-1, but, unlike monocytes, both MDC populations constitutively express COX-2. However, COX-2 regulation in both MDC populations differs from monocytes, as IL-4 does not suppress enzyme expression. COX-2 is functional in MDC as a specific inhibitor, NS-398, significantly reduces PGE(2) production. I-MDC undergoing maturation with soluble CD40 ligand (sCD40L) increase PGE(2) synthesis, but prostanoid synthesis is switched to COX-1. However, with IFN-gamma present, sCD40L-stimulated PG metabolism is redirected to COX-2, and PGE(2) synthesis increases severalfold. Endogenous PG production by MDC does not regulate CD40, CD80, CD86, or HLA DR expression; however, it does promote MDC maturation, as NS-398 significantly reduces CD83 expression in I-MDC matured with sCD40L/IFN-gamma. PG produced through COX-2 also autoregulate IL-12, but the effects are dependent on the MDC maturation state. Blocking COX-2 reduces I-MDC secretion of IL-12p40, whereas it increases IL-12p40 and p70 production by maturing MDC. COX-2-mediated PG production impacts MDC function as maturing these cells in the presence of NS-398 yields MDC that stimulate significantly more IFN-gamma in an allogeneic mixed lymphocyte response than MDC matured without this inhibitor. These studies demonstrate that MDC express both COX isoforms constitutively and produce prostanoids, which autoregulate their maturation and function.

Interactions of HIV-1 with antigen-presenting cells

There is currently much interest in the numerical and functional loss of antigen-presenting cells (APC) in HIV-1 disease and the contribution that this may make to HIV-1 pathology. The HIV-1 virus can interfere with the normal function of APC in a number of ways involving inappropriate signalling. These include changes in cytokine balance, cell-surface molecule expression and intracellular signalling pathways. This review examines how HIV-1 is able to disregulate APC function and discusses possible outcomes for the function of the immune system.

C5a Suppresses the Production of IL-12 by IFN-γ-Primed and Lipopolysaccharide-Challenged Human Monocytes

IL-12 is a key mediator of the immune response, skewing T lymphocytes toward a type 1 cytokine pattern. Priming with IFN-γ or GM-CSF is required for expression of IL-12p70 by cells in which IL-12 is inducible by bacterial products such as LPS. We here show for the first time that the production of bioactive IL-12 by human monocytes can be significantly suppressed by C5a if applied to IFN-γ-primed monocytes before LPS stimulation. There was a dose-dependent suppression by IL-12 (p70) on the levels of intracellular cytokine production and cytokine secretion. mRNA studies consistently showed a reduction of IL-12p40 and IL-12p35 expression by stimulation in the presence of C5a. The results of several different experimental approaches suggest that IL-12 down-regulation was not due to endogenous IL-10, IL-4, or PGE2 production induced by C5a. Moreover, stimulation of IFN-γ-primed monocytes with C5a did not lead to a down-regulation of the CD14 Ag, which is an LPS receptor. These findings show that the anaphylatoxin C5a has the capacity to directly interact with the complex regulation of IL-12.

The toxicology of interleukin-12: a review

Recombinant murine interleukin (IL)-12 (rmIL-12) exhibits antitumor, antiviral, and antimicrobial activities and can modify allergic inflammatory reactions in animal models. Recombinant human IL-12 (rhIL-12) is currently in clinical trials for treatment of cancer, asthma, and viral hepatitis. Principally a phagocyte-derived cytokine, IL-12 targets natural killer cells and T lymphocytes, stimulating their activity and the secretion of interferon (IFN)-gamma. An understanding of the toxicology of IL-12, due in part to effects mediated by IFN-gamma, has emerged from preclinical safety and mechanistic studies and initial clinical trials. Target organs common to several animal species and humans include the lymphohematopoietic system, intestines, liver, and lung.

The paradigm of Th1 and Th2 cytokines: its relevance to autoimmunity and allergy

In the past few years, considerable evidence has accumulated to suggest the existence of functionally polarized responses by the CD4+ T helper (Th)--and the CD8+ T cytotoxic (Tc)-cell subsets that depend on the cytokines they produce. The Th1 and Th2 cellular immune response provide a useful model for explaining not only the different types of protection, but also the pathogenic mechanisms of several immunopathological disorders. The factors responsible for the polarization of specific immune response into a predominant Th1 or Th2 profile have been extensively investigated in mice and humans. Evidence has accumulated from animal models to suggest that Th1-type lymphokines are involved in the genesis of organ-specific autoimmune diseases, such as experimental autoimmune uveitis, experimental allergic encephalomyelitis, or insulin-dependent diabetes mellitus. Accordingly, data so far available in human diseases favor a prevalent Th1 lymphokine profile in target organs of patients with organ-specific autoimmunity. By contrast, Th2-cell predominance was found in the skin of patients with chronic graft-versus host disease, progressive systemic sclerosis, systemic lupus erythematosus, and allergic diseases. The Th1/Th2 concept suggests that modulation of relative contribution of Th1- or Th2-type cytokines regulate the balance between protection and immunopathology, as well as the development and/or the severity of some immunologic disorders. In this review, we have discussed the paradigm of Th1 and Th2 cytokines in relation to autoimmunity and allergy.