Lipopolysaccharide promotes and augments metal allergies in mice, dependent on innate immunity and histidine decarboxylase

Dual effect of nickel on L-arginine/nitric oxide system in RAW 264.7 macrophages

The immunogenic mechanisms of the potent contact allergen nickel are not completely clear. Nitric oxide (NO) serves as a fundamental signalling and effector molecule in the immune system, but little is known about its possible role in immune reactions elicited by nickel. We investigated the effects of nickel on the L-arginine/inducible NO synthase (iNOS) system in a murine macrophage cell line, RAW 264.7. Both LPS-stimulated and non-stimulated RAW 264.7 cells were incubated in the presence of 0-100 μM nickel sulphate for 24 h. Subsequently, NO production, iNOS protein expression, L-arginine uptake and gene expression of iNOS and cationic amino acid transporter systems (CAT) were measured. We found that 100 μM NiSO4 increased LPS-induced nitrite production as well as the formation of [(3)H]-L-citrulline from [(3)H]-L-arginine in the RAW 264.7 cells. Correspondingly, the expression of iNOS gene and protein was also remarkably enhanced. Nevertheless, nickel had an inhibitory effect on L-arginine transport which disappeared gradually upon LPS-stimulation in parallel with an increase in NO output. LPS was found to significantly amplify CAT-3 as well as CAT-2 mRNA expression, mirroring the increase in L-arginine transport. In the range of 1-10 μM, NiSO4 did not have any additional effect on CAT mRNA expression, but at 100 μM it was able to enhance CAT-1 and CAT-3 mRNA expression upon LPS stimulation. Our data indicate that nickel interferes with macrophages' L-arginine/NOS system on multiple levels. Considering the potent biological effects of NO, these influences may contribute to nickel toxicity.

Induction of contact hypersensitivity in the mouse model

Contact hypersensitivity (CHS) in the mouse model is a standard method to assess delayed type hypersensitivity (DTH) responses in the skin induced by low molecular weight chemicals that in humans cause contact dermatitis. These responses are clinically important and present as eczematous skin reactions. Here, this chapter describes the standard protocol for T cell-mediated CHS and a variation thereof, which allows to address more specific questions regarding immunologic pathomechanisms.

Contact dermatitis: from pathomechanisms to immunotoxicology

Contact allergens are small reactive chemicals. They cause allergic contact dermatitis (ACD) by activating the innate and adaptive immune system. Contact allergens are very peculiar because of their built-in autoadjuvanticity that allows them to trigger sterile inflammation following skin penetration. The innate inflammatory response involves the triggering of pattern recognition receptors either by direct chemical interaction with such receptors or by induction of endogenous activators. I discuss here the recent findings regarding prevalence and predisposition, the identification of innate immune and stress response mechanisms relevant for sensitization and the orchestration of the innate and adaptive immune response to contact allergens. Despite still significant gaps of knowledge, recent advances in our understanding of the immunopathogenesis of ACD can now be used for the development of causative treatment strategies and of in vitro alternatives to animal testing for the identification of contact allergens in immunotoxicology.

Mechanisms of chemical-induced innate immunity in allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most prevalent occupational skin diseases and causes severe and long-lasting health problems in the case of chronification. It is initiated by an innate inflammatory immune response to skin contact with low molecular weight chemicals that results in the priming of chemical-specific, skin-homing CD8(+) Tc1/Tc17 and CD4(+) Th1/Th17 cells. Following this sensitization step, T lymphocytes infiltrate the inflamed skin upon challenge with the same chemical. The T cells then exert cytotoxic function and secrete inflammatory mediators to produce an eczematous skin reaction. The recent characterization of the mechanisms underlying the innate inflammatory response has revealed that contact allergens activate innate effector mechanisms and signalling pathways that are also involved in anti-infectious immunity. This emerging analogy implies infection as a potential trigger or amplifier of the sensitization to contact allergens. Moreover, new mechanistic insights into the induction of ACD identify potential targets for preventive and therapeutic intervention. We summarize here the latest findings in this area of research.

The elicitation step of nickel allergy is promoted in mice by microbe-related substances, including some from oral bacteria

Microbial components activate the host's innate immunity via interactions with molecules including TLRs and NODs. We previously reported that in mice (i) Escherichia coli lipopolysaccharide (LPS; TLR4 agonist) promotes Ni-allergy even in T-cell-deficient mice, (ii) E. coli LPS reduces the minimum allergy-inducing concentrations of Ni at both the sensitization and elicitation steps, and (iii) various microbe-related substances promote sensitization to Ni. Here, we examined the effects of microbe-related substances at the elicitation step. Mice (except for TLR4-mutated C3H/HeJ mice) were sensitized to Ni by intraperitoneal injection of NiCl(2) + E. coli LPS. Ten days later their ear-pinnas were challenged with 1 μM NiCl(2) with or without a test substance. Although NiCl(2) alone at this concentration does not induce Ni-allergy, its combination with the following substances induced Ni-allergy in BALB/c mice: LPS preparations from oral gram-negative bacteria (Prevotella intermedia and Porphyromonas gingivalis), a mannan preparation from a fungus (Saccharomyces cerevisiae), and synthetic NOD2 and TLR2 agonists. The effect of the mannan preparation was small in C3H/HeJ mice (sensitized with NiCl(2) + the P. intermedia preparation). The P. intermedia preparation promoted Ni-allergy in C3H/HeJ and nude mice, but not in mice deficient in either TLR2 or histidine decarboxylase. Intragingival injection of the P. intermedia preparation and later challenge with NiCl(2) alone to ear-pinnas also promoted Ni-allergy. These results indicate that (i) in Ni-allergy, a microbial milieu or innate immunity is important at the elicitation step, too, and (ii) some oral bacteria may promote Ni-allergy via TLR2-stimulant(s) production.

Nickel allergy-promoting effects of microbial or inflammatory substances at the sensitization step in mice

Microbial components stimulate innate immunity via Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs), and/or IL-1. We recently reported that in mice, Escherichia coli lipopolysaccharide (LPS, TLR4-ligand) promotes allergic responses to nickel (Ni) at both the sensitization and elicitation steps. Here, we examined in mice the effects of administering other microbial or inflammatory materials at the Ni-sensitization step. A mixture of 1mM NiCl(2) and a test solution was injected into BALB/c mice intraperitoneally (0.1 ml/10 g body weight), and 10 days later 5mM NiCl(2) was challenged intradermally into the ear pinnas of the mice (20 μl/ear). The following preparations or substances exhibited adjuvant activities: Prevotella intermedia LPS, Saccharomyces cerevisiae mannan, a synthetic muramyl dipeptide (NOD2-stimulating cell-wall component of bacteria), Pam(3)Cys-SKKKK (TLR2-stimulating synthetic peptide), poly I:C (TLR3-stimulating double-stranded RNA), concanavalin A (a typical T-cell mitogen and T-cell-mediated hepatitis-inducer), heat-killed Propionibacterium acnes (Gram-positive bacterium that causes pimples and induces macrophage-mediated experimental hepatitis), and nitrogen-containing bisphosphonates (chemicals stimulating IL-1 production). Unexpectedly, P. intermedia LPS, which displayed the most potent adjuvant activity among the tested preparations, was effective in TLR4-dysfunctional mutant mice, but not in TLR2-deficient mice, whereas the reverse was true for S. cerevisiae mannan. These results suggest that (i) for the establishment of Ni-allergy in mice, stimulation of innate immunity (including TLRs, NLRs, IL-1 production, and/or other factors) may be important at the sensitization step, and (ii) P. intermedia may produce a substance(s) that potently promotes Ni-allergy via stimulation of TLR2.

Involvement of prostaglandins and histamine in nickel wire-induced acute inflammation in mice

The irritancy of Nickel (Ni) ions has been well documented clinically. However, the chemical mediators involved in the acute inflammation induced by solid Ni are not fully understood. We used the Ni wire-implantation model in mice and examined roles of prostaglandins and histamine in plasma leakage in the acute phase. The subcutaneous implantation of a Ni wire into the back of mice induced plasma leakage from 8 to 24 h and tissue necrosis around the wire at 3 days, whereas the implantation of an aluminum wire induced no such inflammatory responses. An increase in the mRNA for cyclooxygenase (COX)-2 and HDC in cells around the Ni wire was detected 4 h after the implantation. The leakage of plasma at 8 h was inhibited by indomethacin in a dose-dependent manner. Dexamethasone and the p38 MAP kinase inhibitor SB203580 also inhibited the exudation of plasma consistent with the inhibition of the expression of COX-2 mRNA. Furthermore, plasma leakage was partially but siginificantly reduced in histamine H1 receptor knockout mice and histidine decarboxylase (HDC) knockout mice but not in H2 receptor knockout mice. These results suggested that the Ni ions released from the wire induced the expression of COX-2 and HDC, resulting in an increase in vascular permeability during the acute phase of inflammation.

Crucial role for human Toll-like receptor 4 in the development of contact allergy to nickel

Allergies to nickel (Ni(2+)) are the most frequent cause of contact hypersensitivity (CHS) in industrialized countries. The efficient development of CHS requires both a T lymphocyte-specific signal and a proinflammatory signal. Here we show that Ni(2+) triggered an inflammatory response by directly activating human Toll-like receptor 4 (TLR4). Ni(2+)-induced TLR4 activation was species-specific, as mouse TLR4 could not generate this response. Studies with mutant TLR4 proteins revealed that the non-conserved histidines 456 and 458 of human TLR4 are required for activation by Ni(2+) but not by the natural ligand lipopolysaccharide. Accordingly, transgenic expression of human TLR4 in TLR4-deficient mice allowed efficient sensitization to Ni(2+) and elicitation of CHS. Our data implicate site-specific human TLR4 inhibition as a potential strategy for therapeutic intervention in CHS that would not affect vital immune responses.

Nickel sensitisation in mice: a critical appraisal

BACKGROUND

The market release of new domestic and industrial chemical and metal products requires certain safety certification, including testing for skin sensitisation. Although various official guidelines have described how such testing is to be done, the validity of the available test models are in part dubious, for which reason regulatory agencies and research aim to further improve and generalise the models for testing of skin sensitisation.

OBJECTIVE

We applied a recently published murine model of nickel allergy as to test its applicability in a regulatory setting and to study and better understand the events leading to type-IV hypersensitivity. Nickel was chosen as model hapten since it induces allergic contact dermatitis with high incidence in the general population.

METHOD

Typically, C57BL/6 mice were sensitised and challenged by intradermal applications of nickel, and cutaneous inflammation was analysed by the mouse ear-swelling test, by histology, and by lymphocyte reactivity in vitro.

RESULT

Surprisingly, the study suggested that the skin reactions observed were results of irritant reactions rather than of adaptive immune responses. Non-sensitised mice responded with cutaneous inflammation and in vitro lymphocyte reactivity which were comparable with nickel-sensitised mice. Furthermore, histological examinations as well as experiments in T-cell deficient mice demonstrated that lymphocytes were not involved and that nickel caused an irritant contact dermatitis rather a true allergic type-IV contact dermatitis.

CONCLUSION

The authors question the validity of the described murine model of nickel allergy.

Promotion of arthritis and allergy in mice by aminoglycoglycerophospholipid, a membrane antigen specific to Mycoplasma fermentans

Mycoplasmas, which lack a cell wall and are the smallest self-replicating bacteria, have been linked to some chronic diseases, such as AIDS, rheumatoid arthritis (RA), and oncogenic transformation of cells. Their membrane components (lipoproteins and glycolipids) have been identified as possible causative factors in such diseases. Glycoglycerophospholipid (GGPL)-III, a unique phosphocholine-containing aminoglycoglycerophospholipid, is a major specific antigen of Mycoplasma fermentans, and has been detected in 38% of RA patients. Unlike those of lipoproteins, which induce inflammation via Toll-like receptor 2 (TLR2), the pathologic effects of GGPL-III are poorly understood. RA and metal allergies are chronic inflammatory diseases in which autoantigens have been implicated. Here, we examined the effects of chemically synthesized GGPL-III in murine arthritis and allergy models. GGPL-III alone exhibited little inflammatory effect, but promoted both collagen-induced arthritis and nickel (Ni) allergy, although less powerfully than Escherichia coli lipopolysaccharide. The augmenting effect of GGPL-III on Ni allergy was present in mice deficient in either T cells or active TLR4, but it was markedly weaker in mice deficient in macrophages, interleukin-1, or the histamine-forming enzyme histidine decarboxylase than in their control strains. These results suggest that GGPL-III may play roles in some types of chronic diseases via the innate immune system.

Beryllium alters lipopolysaccharide-mediated intracellular phosphorylation and cytokine release in human peripheral blood mononuclear cells

Beryllium exposure in susceptible individuals leads to the development of chronic beryllium disease, a lung disorder marked by release of inflammatory cytokine and granuloma formation. We have previously reported that beryllium induces an immune response even in blood mononuclear cells from healthy individuals. In this study, we investigate the effects of beryllium on lipopolysaccharide-mediated cytokine release in blood mononuclear and dendritic cells from healthy individuals. We found that in vitro treatment of beryllium sulfate inhibits the secretion of lipopolysaccharide-mediated interleukin 10, while the release of interleukin 1beta is enhanced. In addition, not all lipopolysaccharide-mediated responses are altered, as interleukin 6 release in unaffected upon beryllium treatment. Beryllium sulfate-treated cells show altered phosphotyrosine levels upon lipopolysaccharide stimulation. Significantly, beryllium inhibits the phosphorylation of signal transducer and activator of transducer 3, induced by lipopolysaccharide. Finally, inhibitors of phosphoinositide-3 kinase mimic the effects of beryllium in inhibition of interleukin 10 release, while they have no effect on interleukin 1beta secretion. This study strongly suggests that prior exposures to beryllium could alter host immune responses to bacterial infections in healthy individuals, by altering intracellular signaling.

Synergistic augmentation of inflammatory cytokine productions from murine mast cells by monomeric IgE and toll-like receptor ligands

Simultaneous activation of murine mast cells by monomeric IgE and toll-like receptor (TLR) ligands was examined. Inflammatory cytokine production elicited by the binding of IgE in the absence of antigen, was further enhanced by the addition of lipopolysaccharide (LPS) or peptidoglycan (PGN). Enhancement by LPS or PGN on cytokine production was mediated by TLR4 and TLR2, respectively, since TLR4- and TLR2-deficient mast cells did not show synergistic activation by monomeric IgE and LPS/PGN. Synergistic activation of mast cells was obtained via phosphorylation of several mitogen-activated protein kinases (MAPK). Furthermore, MAPK inhibitors, significantly attenuated the augmentation of inflammatory cytokine production by monomeric IgE and LPS or PGN. Altogether, these results suggest that simultaneous TLR activation of mast cells with IgE molecules, particularly highly cytokinergic (HC) IgE, might contribute to the exacerbation of allergic diseases associated with infection even in the absence of a specific antigen.

The foreign body reaction in T-cell-deficient mice

The role(s) of T lymphocytes in the foreign body response has not been thoroughly elucidated. Lymphocytes are known to augment macrophage adhesion and fusion in vitro. Furthermore, T lymphocytes are a possible source of the cytokines, IL-4 and IL-13, which induce macrophage fusion. In this study, we used BALB/c mice and BALB/c (nu/nu) nude mice to investigate foreign body giant cell (FBGC) formation in a T-cell-deficient setting. Mice were implanted with Elasthane 80A (PEU), silicone rubber (SR), or poly(ethylene terephthalate) (PET) for 7, 14, or 21 days using the cage implant system. Exudate cells and IL-4 and IL-13 levels in exudate supernatants were analyzed by flow cytometry and a multiplex immunoassay, respectively, at Days 7, 14, and 21. Macrophage adhesion and fusion on material surfaces were analyzed using optical microscopy. T-cell-deficient mice had lower total leukocyte concentrations at the biomaterial implant site at all time points. Adherent cell density was comparable between normal and T-cell-deficient mice except in the PEU group at Day 21. However, percent fusion, average nuclei per FBGC, and FBGC morphology were comparable between normal and T-cell-deficient mice. IL-4 was not detected in any sample, but IL-13 levels were also comparable between normal and T-cell-deficient mice indicating Th2-polarized T-cells are not the sole source of this cytokine. We have shown that there are pathways that do not require thymus-matured T lymphocytes, which lead to a normal foreign body response to biomaterials in a murine model.

Nickel induces secretion of IFN-gamma by splenic natural killer cells

Although nickel hypersensitivity is known as a delayed-type hypersensitivity mediated by nickel-specific T cells, it is greatly influenced by other immune cells. Here we show that splenic natural killer cells (NK cells) directly or indirectly respond to nickel by secretion of IFN-gamma. Using enzyme-linked immunosorbent spot (ELISPOT) assays, we found that nickel-reactive cells readily secreted IFN-gamma when splenocytes were cultured in the presence of varying concentrations of nickel sulfate (NiSO(4)) for 24 h. However, nickel-reactive IL-2- or IL- 4-secreting cells were infrequent during the 24-h culture with NiSO(4). Immune responses to nickel were innate, not adaptive, in nature since the frequency of nickel-reactive IFN-g-secreting cells did not increase upon previous exposure to NiSO(4) and recombination activating gene (RAG)-1-deficient mice contained nickel-reactive IFN-gamma-secreting cells. The involvement of NK cells in the innate response to NiSO(4) was confirmed since we could observe a significant reduction of the frequency of nickel-reactive cells in NK cell-depleted mice. Furthermore, the number of IFN-gamma secreting cells was significantly reduced in the ELISPOT assays when NKG2D was blocked by anti-NKG2D antibody. These results suggest that there is an early and rapid innate immune response to nickel, which is mediated by NK cells and the NKG2D receptor. The significance of the innate response to nickel is that it may contribute to development of the late T cell-mediated delayed type hypersensitivity against nickel.

Biotin status affects nickel allergy via regulation of interleukin-1beta production in mice

Biotin, a water-soluble B complex vitamin, is possibly involved in chronic inflammatory diseases, although the detailed mechanisms are unclear. In this study, we investigated the effects of biotin status on nickel (Ni) allergy in mice. Mice were fed a basal or biotin-deficient (BD) diet for 8 wk and sensitized with an intraperitoneal injection of NiCl(2) and lipopolysaccharide. Ten days after sensitization, NiCl(2) was intradermally injected into pinnas and ear swelling was measured. For in vitro analysis, we cultured a murine macrophage cell line, J774.1, under a biotin-sufficient (C, meaning control) or BD condition for 4 wk and analyzed interleukin (IL)-1 production. Significantly higher ear swelling was induced in BD mice than C mice. Adaptive transfer of splenocytes from both C and BD mice induced Ni allergy in unsensitized mice. Regardless of donor mice, ear swelling was significantly higher in BD recipient mice than C recipient mice. Ni allergy was not induced in either C or BD IL-1(-/-) mice. Splenocytes from BD mice produced a significantly higher amount of IL-1beta than those from C mice. Production and mRNA expression of IL-1beta were significantly higher in BD J774.1 cells than in C cells. Biotin supplementation inhibited the augmentation of IL-1beta production in vitro. In vivo supplementation of biotin in drinking water dose-dependently decreased ear swelling in C and BD mice. These results indicate that biotin status affects Ni allergy in the elicitation phase via the upregulation of IL-1beta production in mice, suggesting that biotin supplementation may have therapeutic effects on human metal allergy.

Adjuvant effect of lipopolysaccharide on the induction of contact hypersensitivity to haptens in mice

BACKGROUND

Toll-like receptor (TLR) 4 is a critical receptor and signal transducer for lipopolysaccharide (LPS), a major component of Gram-negative bacteria. The MyD88-independent pathway downstream of TLR4 leads to functional dendritic cell (DC) maturation, although LPS-induced cytokine production from DCs is MyD88-dependent.

OBJECTIVES

We investigated whether intracutaneously injected LPS alters the functions of cutaneous DCs, leading to enhanced contact hypersensitivity (CH).

METHODS

The ear swelling response was measured to evaluate the magnitude of CH. Cell proliferation of allogeneic splenocytes stimulated by DC-enriched draining lymph node (LN) cells was measured by performing a [(3)H]-thymidine incorporation assay. Epidermal I-A+ cells were evaluated under an epifluorescent microscope. I-A+ FITC-bearing cells from the draining LNs 24h after FITC application were analyzed on FACScan.

RESULTS

LPS augmented CH induction in C3H/HeN (HeN) and MyD88-knockout (KO) mice but not in C3H/HeJ (HeJ) and H-2S(d)-bearing strains such as BALB/c mice. LPS failed to augment the allo-stimulatory ability of DCs in the draining LNs after hapten applications. LPS altered the density and morphology of epidermal I-A+ cell in HeN and BALB/c mice but not in TLR4-deficient HeJ mice. LPS increased the proportion of I-A+ FITC-bearing cells in the LNs 24h after FITC application in HeN, but not in BALB/c and HeJ.

CONCLUSIONS

LPS augments the ability of DCs to migrate to the draining LNs, leading to enhanced CH via a TLR4-dependent, MyD88-independent pathway. The different effects of LPS on CH in some strains of mice may explain individual differences in the susceptibility to establish CH to daily antigen exposures in clinical settings.