Histamine regulation of interleukin-18-initiating cytokine cascade is associated with down-regulation of intercellular adhesion molecule-1 expression in human peripheral blood mononuclear cells

Expression of Histidine Decarboxylase and Its Roles in Inflammation

Histamine is a well-known mediator of inflammation that is released from mast cells and basophils. To date, many studies using histamine receptor antagonists have shown that histamine acts through four types of receptors: H1, H2, H3, and H4. Thus, histamine plays more roles in various diseases than had been predicted. However, our knowledge about histamine-producing cells and the molecular mechanisms underlying histamine production at inflammatory sites is still incomplete. The histamine producing enzyme, histidine decarboxylase (HDC), is commonly induced at inflammatory sites during the late and chronic phases of both allergic and non-allergic inflammation. Thus, histamine levels in tissues are maintained at effective concentrations for hours, enabling the regulation of various functions through the production of cytokines/chemokines/growth factors. Understanding the regulation of histamine production will allow the development of a new strategy of using histamine antagonists to treat inflammatory diseases.

Histamine and diabetic nephropathy: an up-to-date overview

The classification of diabetic nephropathy (DN) as a vascular complication of diabetes makes the possible involvement of histamine, an endogenous amine that is well known for its vasoactive properties, an interesting topic for study. The aim of the present review is to provide an extensive overview of the possible involvement of histamine in the onset and progression of DN. The evidence collected on the role of histamine in kidney function together with its well-known pleiotropic action suggest that this amine may act simultaneously on glomerular hyperfiltration, tubular inflammation, fibrosis development and tubular hypertrophy.

Eosinophils and mast cells in leishmaniasis

Leishmania spp. are parasitic protozoa endemic in tropical and subtropical regions and the causative agent of leishmaniasis, a collection of syndromes whose clinical manifestations vary according to host and pathogen factors. Leishmania spp. are inoculated into the mammalian host by the bite of an infected sand fly, whereupon they are taken up by phagocytosis, convert into the replicative amastigote stage within macrophages, reproduce, spread to new macrophages and cause disease manifestations. A curative response against leishmaniasis depends in the classical activation of macrophages and the IL-12-dependent onset of an adaptive type 1 response characterized by the production of IFN-γ. Emerging evidence suggests that neutrophils, dendritic cells and other immune cells can serve as either temporary or stable hosts for Leishmania spp. Furthermore, it is becoming apparent that the initial interactions of the parasite with resident or early recruited immune cells can shape both the macrophage response and the type of adaptive immune response being induced. In this review, we compile a growing number of studies demonstrating how the earliest interactions of Leishmania spp. with eosinophils and mast cells influence the macrophage response to infection and the development of the adaptive immune response, hence, determining the ultimate outcome of infection.

Role of histamine and its receptors in cerebral ischemia

Histamine is recognized as a neurotransmitter or neuromodulator in the brain, and it plays a major role in the pathogenic progression after cerebral ischemia. Extracellular histamine increases gradually after ischemia, and this may come from histaminergic neurons or mast cells. Histamine alleviates neuronal damage and infarct volume, and it promotes recovery of neurological function after ischemia; the H1, H2, and H3 receptors are all involved. Further studies suggest that histamine alleviates excitotoxicity, suppresses the release of glutamate and dopamine, and inhibits inflammation and glial scar formation. Histamine may also affect cerebral blood flow by targeting to vascular smooth muscle cells, and promote neurogenesis. Moreover, endogenous histamine is an essential mediator in the cerebral ischemic tolerance. Due to its multiple actions, affecting neurons, glia, vascular cells, and inflammatory cells, histamine is likely to be an important target in cerebral ischemia. But due to its low penetration of the blood-brain barrier and its wide actions in the periphery, histamine-related agents, like H3 antagonists and carnosine, show potential for cerebral ischemia therapy. However, important questions about the molecular aspects and pathophysiology of histamine and related agents in cerebral ischemia remain to be answered to form a solid scientific basis for therapeutic application.

An isomeric mixture of novel cerebrosides isolated from Impatiens pritzellii reduces lipopolysaccharide-induced release of IL-18 from human peripheral blood mononuclear cells

An isomeric mixture of two cerebrosides, soya-cerebrosides I and II, was isolated from an ethno drug, the rhizomes of Impatiens pritzellii Hook. f. var. hupehensis Hook. f., and their structures were identified by spectroscopic (NMR, MS) analysis. In order to determine the immunomodulatory activities of soya-cerebrosides I and II, the effects of the mixture of cerebrosides (MC) on cytotoxicity of human peripheral blood mononuclear cells (PBMC) and the inhibitory activities to lipopolysaccharide (LPS)-induced interleukin (IL)-18 in PBMC were studied. The MC at concentrations of 10 and 1 microM, without toxicity to PBMC in 24 h, showed obvious inhibitory activity on IL-18 secretion. Because of this effect of modulating the cellular immune response, soya-cerebrosides I and II were considered to be the active substances of this ethno drug.

Histamine inhibits advanced glycation end products-induced adhesion molecule expression on human monocytes

Advanced glycation end products (AGEs) are modifications of proteins/lipids that become nonenzymatically glycated after contact with aldose sugars. Among various subtypes of AGEs, glyceraldehyde-derived AGE (AGE-2) and glycolaldehyde-derived AGE (AGE-3) are suggested to play roles in inflammation in diabetic patients. Because the engagement of intercellular adhesion molecule (ICAM)-1, B7.1, B7.2, and CD40 on monocytes with their ligands on T cells plays roles in cytokine production, we examined the effects of AGE-2 and AGE-3 on the expression of adhesion molecules and cytokine production in human peripheral blood mononuclear cells (PBMC) and their modulation by histamine in the present study. AGE-2 and AGE-3 induced the expressions of ICAM-1, B7.1, B7.2, and CD40 on monocytes and the production of interferon-gamma in PBMC. Histamine concentration-dependently inhibited the action of AGE-2 and AGE-3. The effects of histamine were antagonized by an H2 receptor antagonist, famotidine, and mimicked by H2/H4 receptor agonists dimaprit and 4-methylhistamine. Histamine induced cAMP production in the presence and absence of AGE-2 and AGE-3. The effects of histamine were reversed by a protein kinase A (PKA) inhibitor, N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89), and mimicked by a dibutyryl cAMP and an adenylate cyclase activator, forskolin. These results as a whole indicated that histamine inhibited the AGE-2- and AGE-3-induced adhesion molecule expression and cytokine production via H2 receptors and the cAMP/PKA pathway.

Cytokine responses of intraepithelial lymphocytes are regulated by histamine H(2) receptor

BACKGROUND

Histamine participates in the immune regulation of several gastrointestinal diseases. However, the effect of histamine on intestinal intraepithelial lymphocytes (IELs), the front line of the intestinal mucosal immune system, is not well understood. We examined whether histamine has a direct effect on cytokine production by IELs and the involvement of histamine receptor subtypes.

METHODS

Murine IELs were activated by PMA plus ionomycin with/without histamine. Secreted cytokines were measured and compared with those of splenocytes. Intracellular cytokines were detected by flow cytometry. Expression of histamine receptor subtypes in IELs was examined by RT-PCR.

RESULTS

Histamine H(1) receptor (H(1)R), H(2)R, and H(4)R, but not H(3)R mRNA were expressed on IELs. Histamine significantly decreased Th1-cytokine (IFN-gamma, TNF-alpha, and IL-2) and also IL-4 production in IELs as well as splenocytes. The selective H(2)R antagonist famotidine, but not the H(1)R antagonist pyrilamine nor the H(3)R/H(4)R antagonist thioperamide, competes with the inhibitory effect of histamine on these cytokine production in IELs. These suppressive effects of histamine were mimicked by a selective H(2)R/H(4)R agonist dimaprit. Further, these suppressive effects of histamine for Th1-cytokine and IL-4 did not accompany the enhancement of IL-10 production or IL-10 mRNA level in IELs. Intracellular cytokine analysis revealed that the number of IFN-gamma-producing alphabeta T cells was significantly reduced by histamine in IELs.

CONCLUSIONS

Histamine has a direct suppressive effect on IEL-derived cytokines via H(2)R, which would have a crucial role in the suppression of local immunoregulation in the intestinal epithelium.

[Inducible histamine protects mice from hepatitis through H2-receptor stimulation]

Histamine is well known for its roles in allergic diseases and anaphylaxis through H(1)-receptor stimulation. The H(1)-receptor stimulation by histamine results in an increase in vascular permeability, vasodilatation, and stimulation of nerve terminals in primary sensory neurons, thereby accelerating the inflammatory responses. On the other hand, histamine has been demonstrated to be involved in the regulation of innate and acquired immune responses through H(2)-receptors. In a previous study with human peripheral blood mononuclear cells, we observed that histamine exerts various regulatory effects on monocyte/macrophage function. In this review, we discuss how inducible histamine protects mice from lethal hepatitis, induced by heat-killed P.acnes (1 mg, i.v.) followed by challenge with a low dose of lipopolysaccharide (1 microg), by reducing the excessive cytokine response in the liver. In addition, from in vivo studies with histidine decarboxylase knockout and H(1)-, H(2)-receptor knockout mice, the protective effect of histamine against fulminant hepatitis is shown to be elicited through H(2)-receptor stimulation.

Impact of systemic histamine deficiency on the crosstalk between mammary adenocarcinoma and T cells

The purpose of the present study was to investigate the influence of lack of histamine (HA) on tumor growth and functions of T cells in order further to illustrate the mechanism of immunological tolerance induction by HA. We assessed the phenotype and cytokine production of splenic lymphocytes in syngeneic HA-free (histidine decarboxylase knock-out) (HDC KO) and wild-type mice, inoculated subcutaneously with the LM2 murine breast cancer cell line. Relative quantification of target mRNA was performed with a TaqMan real-time RT-PCR assay. The CD4(+)CD25(high+) Treg cell numbers were significantly smaller in the tumor-bearing KO mice than in the wild type ones measured by flow-cytometry. The expression of forkhead box P3 (Foxp3) decreased significantly and the copies of splenic Tbox-21 (T-bet) transcriptional factor mRNA was higher in HDC KO tumor-bearing mice than those of normal mice. The cytokine levels showed that a smaller number of interleukin-13-producing Th2 cells were elicited compared to interferon-gamma-producing Th1 cells in the tumor-bearing HDC KO mice. In conclusion, the present study demonstrates that endogenous histamine stimulates the growth of breast adenocarcinoma tumor implants in mice by suppressing anti-tumor immunity.

Suppression of inflammatory cell recruitment by histamine receptor stimulation in ischemic rat brains

Inflammation is a crucial factor in the development of ischemia-induced brain injury. Since facilitation of central histaminergic activity ameliorates reperfusion injury, effects of postischemic administration of L-histidine, a precursor of histamine, and thioperamide, a histamine H3 receptor antagonist, on inflammatory cell infiltration were evaluated in a rat model of transient occlusion of the middle cerebral artery. After reperfusion for 12, 24, or 72 h following 2 h of occlusion, brain slices were immunohistochemically stained with antibodies against myeloperoxidase and CD68, which were markers of polymorphonuclear leukocytes and macrophages/microglia, respectively. After reperfusion for 12-24 h, the number of neutrophils on the ischemic side increased markedly, whereas the increase was not observed on the contralateral side. Administration of L-histidine (1000 mg/kg x 2, i.p.), immediately and 6 h after reperfusion, reduced the number of neutrophils to 52%. Simultaneous administration of thioperamide (5 mg/kg, s.c.) further decreased the number of neutrophils to 32%. Likewise, the ischemia induced increase in the number of CD68-positive cells after 24 h was suppressed by L-histidine injections. The L-histidine administration decreased the number of CD4+ T lymphocytes on both ischemic and contralateral sides after 12 h, and concurrent administration of thioperamide prolonged the effect. Although administration of mepyramine (3 nmol, i.c.v.) did not affect suppression of leukocyte infiltration, ranitidine tended to reverse the effect of L-histidine. These data suggest that enhancement of central histaminergic activity suppresses inflammatory cell recruitment after ischemic events through histamine H2 receptors, which may be a mechanism underlying the protective effect of L-histidine.

The role of histamine in the intracellular survival of Mycobacterium bovis BCG

The course and outcome of infection with mycobacteria are determined by a complex interplay between the immune system of the host and the survival mechanisms developed by the bacilli. Histamine plays an important role in various processes, including cell division, metabolism, and apoptosis, and it modulates innate and adaptive immune responses. In the present study we investigated the intracellular survival of Mycobacterium bovis BCG in murine bone-marrow macrophages isolated from wild-type (WT) and histidine-decarboxylase knock-out [HDC (-/-)] mice. Mycobacterial titers were significantly higher in the HDC (-/-) macrophages as compared with the WT cells. M. bovis BCG growth in WT macrophages could be enhanced by pyrilamine and cimetidine. Exogenously added histamine decreased the intracellular counts of M. bovis BCG in HDC (-/-) macrophages. Infection of activated macrophages with M. bovis BCG elicited apoptosis, but there was no significant difference between the WT and the HDC (-/-) cells. These bacilli induced comparable levels of tumor necrosis factor-alpha production in the WT and the HDC (-/-) macrophages. M. bovis BCG stimulated interleukin-18 (IL-18) production in the macrophages from WT mice, but not in the HDC (-/-) cells. Exogenously added IL-18 decreased the titers of intracellular mycobacteria in HDC (-/-) cells. In conclusion, these data implicate histamine in the intracellular survival of M. bovis BCG. The cellular control mechanisms restricting the growth of M. bovis BCG are complex and involve H1 and H2 receptor-mediated events. Histamine might be an important mediator of M. bovis BCG-induced IL-18 production, which in turn contributes to immune protection.

Involvement of prostaglandin receptors (EPR2–4) in in vivo immunosuppression of PGE2 in rat skin transplant model

BACKGROUND

Prostaglandin E2 (PGE2) is known to modulate immune responses and is widely viewed as a general immunosuppressant. There have been recognized four receptors for PGE2 (EP1-EP4 receptor) so far, and EP2 and EP4 receptors are mainly involved in the immunosuppressive effect of PGE2 in vitro. In the present study we examined the in vivo immunosuppressive effects of selective EP receptor agonists using a high-responder rat skin transplantation model.

MATERIALS AND METHODS

Skin allografts from ACI donors were transplanted onto LEW recipients. Agents were injected everyday between day 0 and day 5 after skin transplantation at the dose of 300 microg/kg subcutaneously. Survival of the skin allograft, histological changes and changes of the intragraft cytokine expressions were analyzed using the reverse transcription polymerase chain reaction (RT-PCR). We also assessed the mixed lymphocyte reaction (MLR) assay using splenocytes.

RESULTS

PGE2 significantly prolonged allograft survival (18.8+/-1.5 days) compared with untreated control (14.8+/-0.8 days). EP2R+EP3R+EP4R agonists also prolonged allograft survival (18.0+/-1.0 days) although EP3R agonist or EP2R+EP4R agonists alone failed (15.5+/-0.7, 15.4+/-1.3 days, respectively). RT-PCR analysis in the skin grafts demonstrated IL-10 up-regulation and IFN-gamma down-regulation in all groups except untreated control and EP2R agonist-treated groups. MLR was significantly reduced in groups of EP2R+EP4R agonists, EP2R+EP3R+EP4R agonists and PGE2, compared with untreated control.

CONCLUSIONS

The effect of PGE2 to prolong the survival of skin transplant requires the action of a combination of three receptors, i.e., EP2+EP3+EP4.

Inducible histamine protects mice from P. acnes-primed and LPS-induced hepatitis through H2-receptor stimulation

BACKGROUND & AIMS

Inducible histamine and histamine H2-receptors have been suggested to be involved in innate immune response.

METHODS

We examined a functional role of inducible histamine in the protection against hepatic injury and lethality in Propionibacterium acnes -primed and lipopolysaccharide-induced hepatitis, using histidine decarboxylase knockout and H2-receptor knockout mice.

RESULTS

Lipopolysaccharide challenge after Propionibacterium acnes priming increased histidine decarboxylase activity in the liver of wild-type mice, associated with a marked elevation of histamine turnover. Histidine decarboxylase-like immunoreactivity was observed in CD68-positive Kupffer cells/macrophages. Treatment of wild-type mice with famotidine or ranitidine but not d -chlorpheniramine augmented hepatic injury and inhibited the survival rate significantly. The same dose of Propionibacterium acnes and lipopolysaccharide induced severe hepatitis and high lethality in histidine decarboxylase knockout and H2-receptor knockout mice; the former were rescued by the subcutaneous injection of histamine. Immunohistochemical study supported the protective role of histamine against the apoptosis of hepatocytes. Histamine suppressed the expression of IL-18 and tumor necrosis factor alpha in the liver, leading to the reduced plasma levels of cytokines including IL-18, TNF-alpha, IL-12, IFN-gamma, and IL-6.

CONCLUSIONS

These findings as a whole indicated that endogenously produced histamine in Kupffer cells/macrophages plays a very important role in preventing excessive innate immune response in endotoxin-induced fulminant hepatitis through the stimulation of H2-receptors.

Histamine inhibits lipopolysaccharide-induced interleukin (IL)-18 production in human monocytes

Lipopolysaccharide (LPS) is an inducer of interleukin (IL)-18, which in turn plays important roles in immune responses. Previously, we reported that tumor necrosis factor (TNF)-alpha production could be detected in human peripheral blood mononuclear cells (PBMCs) treated with relatively low concentration of LPS (1 ng/ml), but that same concentration of LPS could not induce IL-18 production. In the present study, we found that LPS at relatively high concentrations (10-1000 ng/ml) induced IL-18 production in a concentration-dependent manner both in monocytes isolated from PBMC, and that histamine (10(-7) to 10(-4) M) inhibited IL-18 production induced by LPS. The studies using receptor subtype-selective agonists and antagonists suggested that the effect of histamine was mediated by H2 receptor but not by H1, H3 and H4 receptors. Therefore, the stimulation of H2 receptor might be beneficial in the treatment of sepsis through inhibiting LPS-elicited IL-18.

Identification of residues in an orthopoxvirus interleukin-18 binding protein involved in ligand binding and species specificity

Interleukin-18 (IL-18) is a critical cytokine in inflammation and adaptive immune responses. The IL-18 binding proteins (IL-18BP) are a family of proteins that bind to, and inhibit the activity of, IL-18. Using point mutagenesis, we analyzed the ectromelia virus IL-18BP to identify residues involved in binding. Because p13 can bind both human and murine IL-18, and because it is highly homologous to the variola virus IL-18BP, we set out to identify residues that may be involved in species specificity. Several of the mutations resulted in complete abrogation of binding affinity. Three (F49A, E77A, and E69A) significantly affected binding with both species of IL-18, but not to the same extent. Mutant H70A showed reduced affinity for human IL-18 while binding to murine IL-18 was not affected. This study demonstrated that interaction of IL-18 with p13 was similar to other IL-18BPs, however, novel species-specific interactions were identified.

Interleukin-18 enhances monocyte tumor necrosis factor alpha and interleukin-1beta production induced by direct contact with T lymphocytes: implications in rheumatoid arthritis

OBJECTIVE

At sites of inflammation, T cells exert pathologic effects through direct contact with monocyte/macrophages, inducing massive up-regulation of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha). We examined the regulatory effects of IL-18 on monocyte activation by direct contact with T lymphocytes in rheumatoid arthritis (RA).

METHODS

Activated T cells were isolated from RA synovial fluid. Resting T cells and monocytes were isolated from peripheral blood mononuclear cells. RA synovial T cells or phytohemagglutinin (PHA)-stimulated T cells were fixed by paraformaldehyde and then cocultured with monocytes at a ratio of 4:1. Levels of TNFalpha, IL-1beta, IL-10, and IL-18 were measured by enzyme-linked immunosorbent assay. Expression of adhesion molecules, IL-18 receptor, and TNF receptors was analyzed by flow cytometry. Expression of NF-kappaB p65, phosphorylated IkappaBalpha, and phosphatidylinositol 3-kinase (PI 3-kinase) p110 was analyzed by Western blotting.

RESULTS

IL-18 dose-dependently enhanced the production of IL-1beta and TNFalpha, but not IL-10, by monocytes following contact with RA synovial T cells or PHA-prestimulated T cells. NF-kappaB inhibitors N-acetyl-L-cysteine and Bay 11-7085 and PI 3-kinase inhibitor LY294002 inhibited the enhancing effects of IL-18, but MAPK p38 inhibitor SB203580, ERK inhibitor PD98059, and JNK inhibitor SP600125 did not. Increased levels of NF-kappaB in the nucleus, phosphorylated IkappaB, and PI 3-kinase were confirmed in monocytes cocultured with PHA-prestimulated T cells, and the levels were further increased by stimulation with IL-18. Neutralizing antibody to IL-18 inhibited monocyte activation induced by direct contact with PHA-prestimulated T cells. Via cell-cell contact, PHA-prestimulated T cells increased autocrine production of IL-18 by monocytes, which was mediated by activation of the NF-kappaB and PI 3-kinase pathways, and up-regulated the expression of the IL-18 receptor in monocytes. IL-18 up-regulated the expression of the TNF receptors vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) on monocytes. Blocking the binding of the TNF receptors VCAM-1 or ICAM-1 on monocytes to their ligands on stimulated T cells suppressed the IL-18-enhanced production of TNFalpha and IL-1beta in monocytes induced by contact with PHA-prestimulated T cells.

CONCLUSION

IL-18 augments monocyte activation induced by contact with activated T cells in RA synovitis, which is dependent on activation of the NF-kappaB and PI 3-kinase pathways. IL-18 up-regulates the expression of the TNF receptors VCAM-1 and ICAM-1 on monocytes, which mediate the enhancing effects of IL-18 on T cell-monocyte contact.

Unique regulation profile of prostaglandin e1 on adhesion molecule expression and cytokine production in human peripheral blood mononuclear cells

In the present study, we examined the effects of prostaglandin E1 (PGE1) on the expression of intercellular adhesion molecule (ICAM)-1, B7.1, B7.2, CD40, and CD40 ligand (CD40L) on peripheral blood mononuclear cells (PBMC) using fluorescence-activated cell sorting analysis as well as its effects on cytokine production using enzyme-linked immunosorbent assay. Whereas no inhibitor of spontaneous expression of adhesion molecules was reported, we found that PGE1 inhibited spontaneous ICAM-1, B7.2, and CD40 expression on monocytes in a concentration-dependent manner but had no effect on the expression of B7.1 and CD40L. Although interleukin (IL)-18 induced the expression of ICAM-1, B7.2, CD40, and CD40L, PGE1 prevented IL-18-induced expression of ICAM-1, B7.2, and CD40. We examined the involvement of five subtypes of PGE1 receptors (IP, EP1, EP2, EP3, and EP4) in the effect of PGE1 on the expression of these adhesion molecules using subtype-specific agonists. Among EP receptor agonists, EP2 and EP4 receptor agonists inhibited IL-18-elicited ICAM-1, B7.2, and CD40 expression. ONO-1301 (IP receptor agonist) prevented the expression of ICAM-1, B7.2, and CD40 regardless of the presence of IL-18 with the same potency as PGE1. The effect of a combination of ONO-1301 and 11-deoxy (D)-PGE1 (EP2/EP4 receptor agonist) on ICAM-1, B7.2, and CD40 expression mimicked that of PGE1. Moreover, PGE1 inhibited the production of IL-12 and interferon-gamma in PBMC in the presence and absence of IL-18, whereas PGE1 induced IL-10 production. In conclusion, IP receptor and EP2/EP4 receptor play an important role in the action of PGE1 on the expression of adhesion molecules on monocytes and cytokine production.

The regulation of ICAM-1 and LFA-1 interaction by autacoids and statins: a novel strategy for controlling inflammation and immune responses

Histamine, prostaglandin E(2), and catecholamines have been demonstrated to regulate the innate and acquired immune responses. In this review, we describe one of the mechanisms common to the action of these agonists; the regulation of the expression of costimulatory adhesion molecules such as ICAM-1 and B7 antigens on monocytes/macrophages. The specific receptor subtypes involved in the action of each agonist were H(2) for histamine, EP(2)/EP(4) for prostaglandin E(2), and beta(2) for catecholamines, all of which are coupled with adenylate cyclase via Gs protein. The regulation of the expression of adhesion molecules by these agonists in turn leads to the modulation of subsequent cytokine production mediated by cell-cell interaction under different stimuli. Histamine is synthesized in monocytes and T cells by the induction of histidine decarboxylase. The inducible histamine has different dynamics from that in storage granules of mast cells and basophils. Also, noradrenaline appears to be synthesized in lymphocytes. Thus, immune cells can produce histamine, prostaglandins, and noradrenaline by themselves and modulate the cell-cell interaction between monocytes and other cells. Some of the inhibitors of HMG-CoA reductase were shown to bind to the ICAM-1-binding domain of LFA-1, reducing the interaction mediated by ICAM-1/LFA-1. The regulation of interaction mediated by adhesion molecules may provide a new target for controlling inflammatory and immune responses.

Histamine inhibits lipopolysaccharide-induced tumor necrosis factor-alpha production in an intercellular adhesion molecule-1- and B7.1-dependent manner

Lipopolysaccharide (LPS) is recognized as a key molecule in the pathogenesis of Gram negative sepsis and septic shock. In the present study, we demonstrate that LPS (1-1000 pg/ml) concentration dependently up-regulated the expression of intercellular adhesion molecule (ICAM)-1, B7.1, and B7.2 on human monocytes using fluorescence-activated cell sorting analysis, and that tumor necrosis factor (TNF)-alpha production induced by LPS in peripheral blood mononuclear cells (PBMCs) was inhibited by the addition of antibodies against these adhesion molecules, suggesting the dependence of TNF-alpha production on cell-cell interaction through these adhesion molecules. Moreover, we found that histamine (10(-7)-10(-4) M) concentration dependently inhibited the expression of ICAM-1 and B7.1, but not B7.2 on monocytes induced by LPS. Histamine also inhibited the responses of TNF-alpha production induced by LPS. The modulatory effects of histamine on ICAM-1 and B7.1 expression and TNF-alpha production were all concentration dependently antagonized by famotidine but not by d-chlorpheniramine and thioperamide, and were mimicked by selective H2-receptor agonists but not by H1-, H3-, and H4-receptor agonists, indicating the involvement of H2-receptors in the histamine action. Dibutyryl cAMP down-regulated ICAM-1 and B7.1 expression on monocytes stimulated by LPS, suggesting the mediation by the cyclic adenosine monophosphate-protein kinase A pathway of H2-receptor activation. These results as a whole indicated that histamine via H2-receptor inhibited the LPS-induced TNF-alpha production through the regulation of ICAM-1 and B7.1 expression, leading to the reduction of innate immune response stimulated by LPS.

Effect of histamine on intercellular adhesion molecule-1 expression and production of interferon-gamma and interleukin-12 in mixed lymphocyte reaction stimulated with interleukin-18

BACKGROUND

Interleukin (IL)-18 was identified as an interferon (IFN)-gamma-inducing factor and was demonstrated to up-regulate the expression of intercellular adhesion molecule (ICAM)-1 on human monocytes. In organ transplantation, elevation of plasma IL-18 levels has been reported during acute rejection. In the present study, we examined the effect of IL-18 on human mixed lymphocyte reaction (MLR), an in vitro model of acute rejection after organ transplantation. We also investigated the modulatory effects of histamine on IL-18 action because histamine has been demonstrated to be a modulator of IL-18 effect and a mediator of inflammation.

METHODS

We measured the expression of ICAM-1 on human monocytes in MLR in the presence or absence of IL-18 by flow cytometer and determined the associated production of IFN-gamma and IL-12 by ELISA. The modulatory effects of histamine and the relevant histamine receptor subtypes were characterized pharmacologically.

RESULTS

The expression of ICAM-1 on monocytes in MLR was markedly enhanced by the addition of IL-18 in a concentration- and time-dependent manner. In parallel to ICAM-1 up-regulation, IL-18 significantly enhanced the production of IFN-gamma and IL-12 in MLR. Histamine concentration-dependently inhibited ICAM-1 expression and cytokine production in MLR stimulated with IL-18, whereas histamine alone did not show any effects on these responses in the absence of IL-18. The effects of histamine on both ICAM-1 expression and cytokine production were mimicked by the selective H2-receptor agonists 4-methylhistamine and dimaprit and were antagonized by the H2-receptor antagonist famotidine but not by H1- and H3-receptor antagonists.

CONCLUSION

IL-18 strongly enhanced human MLR with respect to ICAM-1 expression and cytokine production. The fact that histamine could inhibit the IL-18-stimulated MLR implies that immunomodulation by histamine and selective H2-receptor agonists may have an important role in future immunosuppressive strategies.

Prostaglandin E(2) inhibits IL-18-induced ICAM-1 and B7.2 expression through EP2/EP4 receptors in human peripheral blood mononuclear cells

Costimulatory molecules play important roles in immune responses. In the present study we investigated the effects of PGE(2) on the expression of ICAM-1, B7.1, and B7.2 on monocytes in IL-18-stimulated PBMC using FACS analysis. Addition of PGE(2) to PBMC inhibited ICAM-1 and B7.2 expression elicited by IL-18 in a concentration-dependent manner. We examined the involvement of four subtypes of PGE(2) receptors, EP1, EP2, EP3, and EP4, in the modulatory effect of PGE(2) on ICAM-1 and B7.2 expression elicited by IL-18, using subtype-specific agonists. ONO-AE1-259-01 (EP2R agonist) inhibited IL-18-elicited ICAM-1 and B7.2 expression in a concentration-dependent manner with a potency slightly less than that of PGE(2), while ONO-AE1-329 (EP4R agonist) was much less potent than PGE(2). The EP2/EP4R agonist 11-deoxy-PGE(1) mimicked the effect of PGE(2) with the same potency. ONO-D1-004 (EP1R agonist) and ONO-AE-248 (EP3R agonist) showed no effect on IL-18-elicited ICAM-1 or B7.2 expression. These results indicated that EP2 and EP4Rs were involved in the action of PGE(2). Dibutyryl cAMP and forskolin down-regulated ICAM-1 and B7.2 expression in IL-18-stimulated monocytes. As EP2 and EP4Rs are coupled to adenylate cyclase, we suggest that PGE(2) down-regulates IL-18-induced ICAM-1 and B7.2 expression in monocytes via EP2 and EP4Rs by cAMP-dependent signaling pathways. The fact that anti-B7.2 as well as anti-ICAM-1 Ab inhibited IL-18-induced cytokine production implies that PGE(2) may modulate the immune response through regulation of the expression of particular adhesion molecules on monocytes via EP2 and EP4Rs.