Increased expression of the novel proinflammatory cytokine high mobility group box chromosomal protein 1 in skin lesions of patients with lupus erythematosus

Transplantation of umbilical cord mesenchymal stem cells alleviates pneumonitis of MRL/lpr mice

OBJECTIVE

To investigate whether the umbilical cord mesenchymal stem cells (UC-MSCs) transplantation in the MRL/lpr mice has effect or not on their pneumonitis and the possible mechanisms underlying this treatment.

METHODS

Twenty four 18-week-old MRL/lpr female mice were divided into three groups as following: the group 2 (UC-MSCT group) have been transplanted with 1×10(6) UC-MSCs through caudal vein, the group 3 (multi-UC-MSCT Group) have been transplanted with 1×10(6) UC-MSCs three times and the group 1 (control group) have been treated with 0.5 mL phosphate buffer saline (PBS) as control. The histopathology of the lung was observed. The pulmonary expression of high mobility group box protein-1 (HMGB-1) was measured by western blot and detected by quantitation real time polymerase chain reaction (PCR). Immunohistochemistry method was used to detect HMGB-1 expressions in pulmo.

RESULTS

In comparision to control ground mice, UC-MSCs significantly reduced interstitial pneumonitis in the MRL/lpr mice. The lung peribronchiolar lesion index of UC-MSCT group (1.40±0.24) and multi-UC-MSCT group (1.02±0.29) were significantly decreased as compared to control group (1.95±0.35) (P<0.01). The perivascular lesion index of UC-MSCT group (1.20±0.18) and multi-UC-MSCT group (1.08±0.16) were also significantly reduced as compared to control group (1.56±0.32) (P=0.018, 0.002) and the lung alveolar areas lesion index of control group (1.72±0.34) was significantly increased as compared to UC-MSCT group (1.30±0.21) and multi-UC-MSCT group (1.05±0.15) (P=0.011, 0.000). The lung HMGB-1 protein in UC-MSCT group (0.32±0.04) and in multi-UC-MSCT group (0.28±0.06) were both significantly decreased as compared to that in control group (0.80±0.21) (P<0.05). The level of HMGB-1 mRNA in UC-MSCT group (4.68±0.37) and in multi-UC-MSCT group (4.35±0.10) lung were both significantly decreased as compared to those in control group (16.29±3.84) (P<0.05). In immunohistochemical staining lung sections, high expression of HMGB-1 was found mainly located in the cytoplasm and extracellular matrix of MRL/lpr mice pulmonary epithelial cells, the expression of HMGB-1 in UC-MSCT group and multi-UC-MSCT group was significantly decreased as compared to that in the control group.

CONCLUSIONS

These findings indicate that UC-MSCs have a therapeutic effect on systemic lupus erythematosus (SLE) pneumonitis, possibly by inhibiting HMGB-1 expression, which suggests a potential application of UC-MSCs in the treatment of human lupus.

Concerted action of Nrf2-ARE pathway, MRN complex, HMGB1 and inflammatory cytokines - implication in modification of radiation damage

Whole body exposure to low linear energy transfer (LET) ionizing radiations (IRs) damages vital intracellular bio-molecules leading to multiple cellular and tissue injuries as well as pathophysiologies such as inflammation, immunosuppression etc. Nearly 70% of damage is caused indirectly by radiolysis of intracellular water leading to formation of reactive oxygen species (ROS) and free radicals and producing a state of oxidative stress. The damage is also caused by direct ionization of biomolecules. The type of radiation injuries is dependent on the absorbed radiation dose. Sub-lethal IR dose produces more of DNA base damages, whereas higher doses produce more DNA single strand break (SSBs), and double strand breaks (DSBs). The Nrf2-ARE pathway is an important oxidative stress regulating pathway. The DNA DSBs repair regulated by MRN complex, immunomodulation and inflammation regulated by HMGB1 and various types of cytokines are some of the key pathways which interact with each other in a complex manner and modify the radiation response. Because the majority of radiation damage is via oxidative stress, it is essential to gain in depth understanding of the mechanisms of Nrf2-ARE pathway and understand its interactions with MRN complex, HMGB1 and cytokines to increase our understanding on the radiation responses. Such information is of tremendous help in development of medical radiation countermeasures, radioprotective drugs and therapeutics. Till date no approved and safe countermeasure is available for human use. This study reviews the Nrf2-ARE pathway and its crosstalk with MRN-complex, HMGB1 and cytokines (TNF-a, IL-6, IFN-? etc.). An attempt is also made to review the modification of some of these pathways in presence of selected antioxidant radioprotective compounds or herbal extracts.

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Exposure to low linear energy transfer (LET) ionizing radiation (IR) causes intracellular oxidative stress and activate the Nrf2-ARE antioxidant pathway.

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Irradiation also causes inflammation and DNA damage which affect other pathways related to MRN complex and HMGB1 proteins.

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The antioxidant Keap1-Nrf2-ARE pathway most importantly regulates intracellular oxidative stress.

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The interaction of Keap1-Nrf2-ARE pathway with HMGB1 regulated inflammation; MRN complex regulated DNA repair is reviewed.

Increase of high mobility group box chromosomal protein 1 in eosinophilic chronic rhinosinusitis with nasal polyps

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized by eosinophil-dominant infiltration in Europe and the United States. However, CRSwNP in Asia has shown different immunopathologic features. High-mobility group protein box 1 (HMGB1) is a DNA-binding protein that has been suggested to be involved in various chronic inflammatory diseases. The objective of this study is to investigate whether HMGB1 is augmented in the Chinese eosinophilic CRSwNP and if non-eosinophilic CRSwNP is associated with interleukin 5 (IL-5), IL-8, and tumor necrosis factor α (TNF-α).

METHODS

Nasal polyps specimens were collected from 41 patients with CRSwNP (20 eosinophilic and 21 non-eosinophilic) undergoing functional endoscopic sinus surgery (FESS). Biopsies of uncinate process, and ethmoidal mucosa from 9 non-CRS patients were used as controls by means of immunohistochemistry (IHC) staining, Western blotting, and quantitative reverse-transcription polymerase chain reaction (qRT-PCR).

RESULTS

HMGB1-positive expression was significantly increased in the epithelium and among the large inflammatory cells infiltration in Eos CRSwNP and non-Eos CRSwNP as compared with controls (p < 0.001). The HMGB1 protein and messenger RNA (mRNA) levels of HMGB1, IL-5, IL-8, and TNF-α were significantly higher in eosinophilic CRSwNP than those from controls and non-eosinophilic CRSwNP, but no significant differences in these markers were found between non-eosinophilic CRSwNP and controls. HMGB1 expression levels correlated significantly and positively with IL-5, IL-8, and TNF-α (rs = 0.665, 0.771, and 0.724, respectively; p < 0.001) and slightly with eosinophil infiltration (rs = 0.149; p = 0.012) and the blood eosinophils count (rs = 0.225; p = 0.001) in all samples.

CONCLUSION

Upregulation of HMGB1 could be a significant marker typically in eosinophilic CRSwNP and it may also contribute to the pathogenesis of CRSwNP along with IL-5, IL-8, and TNF-α.

A possible role of HMGB1 in DNA demethylation in CD4+ T cells from patients with systemic lupus erythematosus

The aberrant activity of CD4⁺ T cells in patients with systemic lupus erythematosus (SLE) is associated with DNA hypomethylation of the regulatory regions in CD11a and CD70 genes. Our previous studies demonstrated that Gadd45a contributes to the development of SLE by promoting DNA demethylation in CD4⁺ T cells. In this study, we identified proteins that bind to Gadd45a in CD4⁺ T cells during SLE flare by using the method of co-immunoprecipitation and mass spectrometry, High mobility group box protein 1 (HMGB1) is one of identified proteins. Furthermore, gene and protein expression of HMGB1 was significantly increased in SLE CD4⁺ T cells compared to controls, and HMGB1 mRNA was correlated with CD11a and CD70 mRNA. A significant, positive correlation was found between HMGB1 mRNA and SLEDAI for SLE patients. Our data demonstrate that HMGB1 binds to Gadd45a and may be involved in DNA demethylation in CD4⁺ T cells during lupus flare.

Cutaneous lupus erythematosus: clinical aspects and molecular pathogenesis

Lupus erythematosus (LE) is an autoimmune disease with diverse clinical manifestations ranging from limited cutaneous (CLE) to potentially life-threatening systemic disease (SLE). Susceptibility to LE arises from genetic variation in multiple loci, and disease activity is provoked by exogenous or endogenous trigger(s), the best characterized of which is exposure to ultraviolet radiation (UVR). Amongst patients with LE, a cluster of photosensitive subjects with cutaneous lesions and positivity for anti-Ro/SSA autoantibodies have been described. The Ro52 antigen belongs to the tripartite motif protein family and has E3 ligase activity. New data reveal that Ro52 ubiquitinates interferon regulatory factors and modulates their transcriptional activity, indicating an important role for Ro52 in inflammation as a negative feedback regulator. Our findings indicate that UVR exposure induces upregulation of Ro52 in the CLE target cell, the keratinocyte, and that Ro52 is upregulated in spontaneous and UVR-induced CLE lesions. Recently described functional analysis of Ro52-deficient mice revealed that loss of Ro52 results in uncontrolled inflammation in response to minor skin injury leading to an LE-like condition. In summary, emerging data suggest that abnormal function or regulation of Ro52 contributes to the pathogenesis of UVR-induced CLE in genetically susceptible individuals. Ro52 may thus be an interesting therapeutic target, as its activation could contribute to downregulation of the chronic inflammatory process in LE. Here, we review the available data on the pathogenesis of CLE and, in particular, the role of the Ro52 autoantigen.

High mobility group box1 (HMGB1) in relation to cutaneous inflammation in systemic lupus erythematosus (SLE)

Summary

Photosensitivity is characteristic of systemic lupus erythematosus (SLE). Upon ultraviolet B (UVB) exposure, patients develop inflammatory skin lesions in the vicinity of sunburn cells (SBCs). High mobility group box 1 (HMGB1) is released from apoptotic and activated cells and exerts inflammatory actions through ligation to its receptors.

Methods

Eleven SLE patients and 10 healthy controls (HCs) were exposed to UVB. Skin biopsies were taken before and at one, three and 10 days after irradiation. Sections were stained for SBC, HMGB1, CD3, CD68, interferon-induced protein MxA and cleaved caspase 3. In vitro experiments with UVB-irradiated keratinocytes were also performed. Higher numbers of cells that had released HMGB1 were seen in the skin of SLE patients compared to HCs before and after irradiation. HMGB1-negative nuclei correlated with the presence of SBCs, and with the number of cleaved caspase 3 positive cells in lupus skin.

Results

HMGB1 release is increased in the skin of SLE patients compared to HCs. Upon UVB exposure, HMGB1 release further increases in SLE patients and is related to the number of apoptotic cells. Our data suggest that HMGB1, probably released from apoptotic keratinocytes, contributes to the development of inflammatory lesions in the skin of SLE patients upon UVB exposure.

Skin recruitment of monomyeloid precursors involves human herpesvirus-6 reactivation in drug allergy

BACKGROUND

In drug-induced hypersensitivity syndrome (DIHS), latent human herpesvirus (HHV)-6 is frequently reactivated in association with flaring of symptoms such as fever and hepatitis. We recently demonstrated an emergence of monomyeloid precursors expressing HHV-6 antigen in the circulation during this clinical course.

METHODS

To clarify the mechanism of HHV-6 reactivation, we immunologically investigated peripheral blood mononuclear cells (PBMCs), skin-infiltrating cells, and lymphocytes expanded from skin lesions of patients with DIHS.

RESULTS

The circulating monomyeloid precursors in the patients with DIHS were mostly CD11b(+) CD13(+) CD14(-) CD16(high) and showed substantial expression of skin-associated molecules, such as CCR4. CD13(+) CD14(-) cells were also found in the DIHS skin lesions, suggesting skin recruitment of this cell population. We detected high levels of high-mobility group box (HMGB)-1 in blood and skin lesions in the active phase of patients with DIHS and showed that recombinant HMGB-1 had functional chemoattractant activity for monocytes/monomyeloid precursors in vitro. HHV-6 infection of the skin-resident CD4(+) T cells was confirmed by the presence of its genome and antigen. This infection was likely to be mediated by monomyeloid precursors recruited to the skin, because normal CD4(+) T cells gained HHV-6 antigen after in vitro coculture with highly virus-loaded monomyeloid precursors from the patients.

CONCLUSIONS

Our results suggest that monomyeloid precursors harboring HHV-6 are navigated by HMGB-1 released from damaged skin and probably cause HHV-6 transmission to skin-infiltrating CD4(+) T cells, which is an indispensable event for HHV-6 replication. These findings implicate the skin as a cryptic and primary site for initiating HHV-6 reactivation.

Increased HMGB1 serum levels and altered HMGB1 expression in patients with psoriasis vulgaris

High mobility group box-1 (HMGB1) has been implicated as a pro-inflammatory cytokine in the pathogenesis of various inflammatory and autoimmune diseases. However, information about HMGB1 in inflammatory skin diseases is unknown. Herein, we investigated the serum HMGB1 levels and tissue HMGB1 expression in patients with psoriasis vulgaris (PV) and atopic dermatitis (AD). Serum levels of HMGB1 in patients with PV and AD were detected by enzyme-linked immunosorbent assay (ELISA). The expression of HMGB1 in lesional skin was evaluated by immunohistochemistry and immunofluorescence. Protein levels of HMGB1 in the nuclear fraction and cytoplasmic fraction were determined by western blot. Serum levels of HMGB1 in patients with PV but not AD were significantly higher than those in nornal controls. Moreover, serum HMGB1 levels were correlated with the severity of PV according to PASI socres. Furthermore, by immunohistochemistry and immunofluorescence, we showed that the expression of HMGB1 in normal skin was almost completely restricted to the nucleus. However, abundant cytoplasmic expression of HMGB1 was observed in the epidermis in lesional skin of PV patients. In addition, western blot data indicated that HMGB1 expression was in the nucleus protein and was absent in the cytoplasm protein in control group. In contrast, HMGB1 expression in the cytoplasmic fraction was detectable in AD patients and more distinct in PV patients. Taken together, this study provides first observations on the association of HMGB1 with PV, and showed the elevated HMGB1 serum levels and altered HMGB1 distribution in lesional skin in patients with PV. We suggest that HMGB1 might be involved in the pathogenesis of PV.

Self double-stranded (ds)DNA induces IL-1β production from human monocytes by activating NLRP3 inflammasome in the presence of anti-dsDNA antibodies

The pathogenic hallmark of systemic lupus erythematosus is the autoimmune response against self nuclear Ags, including dsDNA. The increased expression of the proinflammatory cytokine IL-1β has been found in the cutaneous lesion and PBMCs from lupus patients, suggesting a potential involvement of this cytokine in the pathogenesis of lupus. IL-1β is produced primarily by innate immune cells such as monocytes and can promote a Th17 cell response, which is increased in lupus. IL-1β production requires cleaving pro-IL-β into IL-1β by the caspase-1-associated multiprotein complex called inflammasomes. In this study we show that self dsDNA induces IL-1β production from human monocytes dependent on serum or purified IgG containing anti-dsDNA Abs by activating the nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome. Reactive oxygen species (ROS) and K(+) efflux were involved in this activation. Knocking down the NLRP3 or inhibiting caspase-1, ROS, and K(+) efflux decreased IL-1β production. Supernatants from monocytes treated with a combination of self dsDNA and anti-dsDNA Ab(+) serum promoted IL-17 production from CD4(+) T cells in an IL-1β-dependent manner. These findings provide new insights in lupus pathogenesis by demonstrating that self dsDNA together with its autoantibodies induces IL-1β production from human monocytes by activating the NLRP3 inflammasome through inducing ROS synthesis and K(+) efflux, leading to the increased Th17 cell response.

Lupus nephritis - alarmins may sound the alarm?

A growing body of literature has documented the elevated levels of the alarmin HMGB1 in lupus skin and serum. Two recent reports highlight the increased expression of HMGB1 in lupus nephritis, within the diseased kidneys or in the urine. Taken together with previous reports, these findings suggest that the interaction of HMGB1 with a variety of receptors, including receptor for advanced glycation end products (RAGE) and Toll-like receptors, might play a role in the pathogenesis of lupus nephritis. These studies introduce urinary HMGB1 as a novel biomarker candidate in lupus nephritis. Whether alarmins would be effective in sounding the alarm at the incipience of renal damage remains to be ascertained.

Proteins derived from neutrophil extracellular traps may serve as self-antigens and mediate organ damage in autoimmune diseases

Neutrophils are the most abundant leukocytes in circulation and represent one of the first lines of defense against invading pathogens. Neutrophils possess a vast arsenal of antimicrobial proteins, which can be released from the cell by a death program termed NETosis. Neutrophil extracellular traps (NETs) are web-like structures consisting of decondensed chromatin decorated with granular and cytosolic proteins. Both exuberant NETosis and impaired clearance of NETs have been implicated in the organ damage of autoimmune diseases, such as systemic lupus erythematosus (SLE), small vessel vasculitis (SVV), and psoriasis. NETs may also represent an important source of modified autoantigens in SLE and SVV. Here, we review the autoimmune diseases linked to NETosis, with a focus on how modified proteins externalized on NETs may trigger loss of immune tolerance and promote organ damage.

U1-small nuclear ribonucleoprotein activates the NLRP3 inflammasome in human monocytes

The NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome is a caspase-1-containing cytosolic protein complex that is essential for processing and secretion of IL-1β. The U1-small nuclear ribonucleoprotein (U1-snRNP) that includes U1-small nuclear RNA is a highly conserved intranuclear molecular complex involved in splicing pre-mRNA. Abs against this self nuclear molecule are characteristically found in autoimmune diseases like systemic lupus erythematosus, suggesting a potential role of U1-snRNP in autoimmunity. Although endogenous DNA and microbial nucleic acids are known to activate the inflammasomes, it is unknown whether endogenous RNA-containing U1-snRNP could activate this molecular complex. In this study, we show that U1-snRNP activates the NLRP3 inflammasome in CD14(+) human monocytes dependently of anti-U1-snRNP Abs, leading to IL-1β production. Reactive oxygen species and K(+) efflux were responsible for this activation. Knocking down the NLRP3 or inhibiting caspase-1 or TLR7/8 pathway decreased IL-1β production from monocytes treated with U1-snRNP in the presence of anti-U1-snRNP Abs. Our findings indicate that endogenous RNA-containing U1-snRNP could be a signal that activates the NLRP3 inflammasome in autoimmune diseases like systemic lupus erythematosus where anti-U1-snRNP Abs are present.

HMGB1: a multifunctional alarmin driving autoimmune and inflammatory disease

HMGB1 is a non-histone nuclear protein that can serve as an alarmin to drive the pathogenesis of inflammatory and autoimmune disease. Although primarily located in the cell nucleus, HMGB1 can translocate to the cytoplasm, as well as the extracellular space, during cell activation and cell death; during activation, HMGB1 can undergo post-translational modifications. The activity of HMGB1 varies with the redox states of the cysteine residues, which are required for binding to TLR4. In addition to stimulating cells directly, HMGB1 can form immunostimulatory complexes with cytokines and other endogenous and exogenous factors. In the synovia of patients with rheumatoid arthritis, as well as animal models of this disease, extranuclear expression of HMGB1 is increased and blockade of HMGB1 expression attenuates disease in animal models. In systemic lupus erythematosus, HMGB1 can be a component of immune complexes containing anti-DNA because of its interaction with DNA. In myositis, expression of HMGB1 is enhanced in inflamed muscle and can perturb muscle function. Together, these findings indicate that HMGB1 might be an important mediator and biomarker in rheumatic diseases as well as a target of new therapy.

Tumor necrosis factor α release in peripheral blood mononuclear cells of cutaneous lupus and dermatomyositis patients

Introduction

Several studies have reported that TNFα is substantially increased within skin lesions of patients with discoid lupus erythematosus (DLE), subacute cutaneous lupus erythematosus (SCLE) and dermatomyositis (DM) compared to controls. Elevated TNFα has been reported in the sera of some patients with systemic lupus erythematosus, DLE and SCLE, but not in the sera of patients with DM. Because of the key pathogenic role of autoimmunity in these diseases, in this study we sought to evaluate TNFα production by a readily available source of immune cells (namely, peripheral blood mononuclear cells (PBMCs)) taken from controls and from patients with cutaneous lupus or DM.

Methods

Freshly isolated PBMCs were cultured overnight, and TNFα protein accumulation in conditioned medium was determined. In addition, flow cytometry using cell-type-specific markers was performed to determine the sources of TNFα. One-way analysis of variance and Dunnett's multiple comparisons test were performed for statistical comparisons.

Results

Accumulation of TNFα protein in conditioned medium containing PBMCs from DLE patients, but not from SCLE, TLE or DM patients, was significantly greater (19-fold) than that from controls (P < 0.001). In DLE PBMCs, increased TNFα was produced by circulating monocytes and myeloid dendritic cells (mDCs). The mean TNFα fluorescence intensity, but not the total number, of both monocytes and mDCs (P < 0.01) from DLE patients was significantly greater (2.3-fold) than that of controls. There were significantly more (13.3-fold) mDCs with intracellular TNFα in blood from DLE patients (P < 0.001) and DM patients (P < 0.001) compared to controls. Most importantly, a positive correlation was seen in DLE patients between their disease activity measured using the Cutaneous Lupus Erythematosus Disease Area and Severity Index and TNFα protein secretion (r = 0.61, P < 0.08).

Conclusions

TNFα protein production by PBMCs is greater in DLE patients than in patients with other cutaneous forms of lupus and DM or in controls. Flow cytometric studies demonstrated that circulating monocytes and mDCs contributed to this increased TNFα production. Monocytes and mDCs are present in lesional skin, and the increased TNFα production by these cells and other PBMCs likely increase the number of inflammatory cells seen in DLE skin relative to other subsets of cutaneous lupus erythematosus and DM. These results provide a possible biological explanation for the denser infiltrate seen in DLE relative to DM.

High-mobility group box 1 represents a potential marker of disease activity and novel therapeutic target in systemic lupus erythematosus

High-mobility group box 1 (HMGB1) protein is a nuclear DNA-binding protein, which functions as an alarmin when released from cells. Recent studies implicate extracellular HMGB1 in the pathogenesis of systemic lupus erythematosus (SLE), a prototypical autoimmune disease characterized by the formation of multiple autoantibodies, especially those directed against nucleosomes and double-stranded (ds)DNA. Elevated concentrations of HMGB1 are observed in sera as well as in skin lesions of patients with lupus. Of importance, serum HMGB1 and anti-HMGB1 autoantibody levels correlate with disease activity. In the blood of patients with SLE, HMGB1 is complexed with nucleosomes, at least partially. Moreover, HMGB1-nucleosome complexes from apoptotic cells activate antigen-presenting cells. Injection of HMGB1-nucleosome complexes into nonautoimmune mice results in the formation of autoantibodies against dsDNA and histones in a Toll-like receptor (TLR) 2-dependent manner. Additionally, HMGB1, as a part of DNA-anti-DNA immune complexes, can interact with receptor for advanced glycation end products (RAGE) on the surface of plasmacytoid dendritic cells and B cells leading to TLR9-dependent interferon (IFN)α release and activation of autoreactive B cells, respectively. HMGB1 attached to neutrophil extracellular traps may contribute to IFNα production by facilitating the recognition of self-nucleic acids. Furthermore, HMGB1, complexed with DNA and pathogenic anti-DNA autoantibodies, activates its receptors, TLR2, TLR4 and RAGE, and may thereby be involved in anti-DNA autoantibody-induced kidney damage in lupus nephritis. Collectively, these findings suggest that HMGB1 is a potential marker of disease activity and, because of its probable involvement in the pathogenesis, a novel therapeutic target in SLE.

Biomarkers in chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD ) is a leading cause of allogeneic hematopoietic stem-cell transplantation-related mortality and morbidity. It is an immune-mediated disorder that can target almost any organ in the body, often with devastating consequences. The immune-suppressive medications currently used to treat it are equally toxic and are often not very effective. At this time, our understanding of its pathophysiology is limited. The discovery of potential biomarkers offers new possibilities in the clinical management of cGVHD. They could potentially be used for diagnosing cGVHD, for predicting or evaluating response to therapy and for unique insights into the pathophysiology underlying the clinical manifestations of cGVHD. Understanding the biological origins of these biomarkers can help us construct a more comprehensive and clinically relevant model for the pathogenesis of this disease. In this article, we review existing evidence for candidate biomarkers that have been identified in the framework of how they may contribute to the pathophysiology of cGVHD. Issues regarding the discovery and application of biomarkers are discussed.

Disturbances of apoptotic cell clearance in systemic lupus erythematosus

Systemic lupus erythematosus is a multifactorial autoimmune disease with an as yet unknown etiopathogenesis. It is widely thought that self-immunization in systemic lupus is driven by defective clearance of dead and dying cells. In lupus patients, large numbers of apoptotic cells accumulate in various tissues including germinal centers. In the present review, we discuss the danger signals released by apoptotic cells, their triggering of inflammatory responses, and the breakdown of B-cell tolerance. We also review the pathogenic role of apoptotic cell clearance in systemic lupus erythematosus.

Expression of antimicrobial peptides in different subtypes of cutaneous lupus erythematosus

BACKGROUND

Antimicrobial peptides (AMPs) are small effector molecules of the innate immune system with well-known antimicrobial activity. Skin infections rarely occur in patients with cutaneous lupus erythematosus (CLE), and AMP expression in CLE has not been previously evaluated.

OBJECTIVES

We aimed to determine the expression of several important AMPs in 3 different subtypes of CLE.

METHODS

Skin lesions were analyzed for the gene and protein expression of human β-defensin (hBD)-1, -2, and -3; RNase-7; the cathelicidin LL-37; and psoriasin (S100A7) using real-time reverse transcriptase polymerase chain reaction and immunohistochemistry.

RESULTS

Skin biopsy specimens of 96 study participants including 47 patients with CLE (15 patients with discoid lupus erythematosus [LE], 11 patients with subacute CLE, and 21 patients with LE tumidus), 34 patients with psoriasis, and 15 healthy control subjects were evaluated in this study. HBD-2, hBD-3, LL-37, and psoriasin were significantly more highly expressed in CLE as compared with healthy controls, and most AMPs were significantly more highly induced in subacute CLE as compared with discoid LE and LE tumidus. AMP gene expression paralleled well with AMP protein expression in CLE and controls. Subacute CLE and discoid LE showed a similar correlation of AMP gene expression (significant correlations between hBD-1 and RNase-7, hBD-2 and hBD-3, hBD-2 and psoriasin, and hBD-3 and psoriasin).

LIMITATIONS

The relatively small number of samples and the lack of analysis of the lesional bacterial colonization are a limitation.

CONCLUSIONS

Several AMPs are increased in CLE at both gene and protein levels. This could explain the low prevalence of skin infections in CLE. It remains to be elucidated whether AMPs play a pathogenic role in CLE.

Inefficient clearance of dying cells in patients with SLE: anti-dsDNA autoantibodies, MFG-E8, HMGB-1 and other players

Systemic lupus erythematosus (SLE) is a complex disease resulting from inflammatory responses of the immune system against several autoantigens. Inflammation is conditioned by the continuous presence of autoantibodies and leaked autoantigens, e.g. from not properly cleared dying and dead cells. Various soluble molecules and biophysical properties of the surface of apoptotic cells play significant roles in the appropriate recognition and further processing of dying and dead cells. We exemplarily discuss how Milk fat globule epidermal growth factor 8 (MFG-E8), biophysical membrane alterations, High mobility group box 1 (HMGB1), C-reactive protein (CRP), and anti-nuclear autoantibodies may contribute to the etiopathogenesis of the disease. Up to date knowledge about these key elements may provide new insights that lead to the development of new treatment strategies of the disease.

Pocket epithelium in the pathological setting for HMGB1 release

High-mobility group box-1 (HMGB1) protein acts as a transcription factor in the nucleus and also as a pro-inflammatory cytokine when released into extracellular fluids. The presence of higher levels of HMGB1 is reported in the gingival crevicular fluid from periodontal patients. Since the proliferation of bacteria within the periodontal pocket is closely involved in the exacerbation of periodontal disease, it is hypothesized that the periodontal pocket causes the release of HMGB1. Immunohistochemical staining of inflamed gingiva revealed that HMGB1 is exclusively dislocated from the nucleus to the cytoplasm in the pocket epithelium, whereas it is mainly present in the nucleus in the gingival epithelium. Butyric acid, an extracellular metabolite from periodontopathic bacteria populating the periodontal pocket, induced the passive release of HMGB1 as a result of eliciting necrosis in the human gingival epithelial cell line. Thus, the periodontal epithelium may provide a unique pathological setting for HMGB1 release by bacterial insult.

Increased expression of guanylate binding protein-1 in lesional skin of patients with cutaneous lupus erythematosus

The large GTPase human guanylate binding protein-1 (GBP-1) is a key mediator of angiostatic effects of inflammation and is induced by interferon (IFN)-α and IFN-γ in endothelial cells (ECs). The aim of this study was to investigate whether GBP-1 is a marker of skin lesions in patients with cutaneous lupus erythematosus (CLE). Western blotting revealed that GBP-1 was in vitro induced by IFN-α and -γ in primary keratinocytes obtained from healthy controls. Moreover, we found that this protein was expressed by keratinocytes and ECs in primary and ultraviolet (UV)-induced skin lesions from patients with various subtypes of CLE, when compared to non-lesional skin. No GBP-1 expression was noted in skin biopsy specimens 24 or 72 h after UV irradiation prior to lesion formation in patients with CLE or in healthy control specimens with or without UV irradiation. Initial findings suggest that GBP-1 is not expressed in other skin diseases with different inflammatory aetiology, such as atopic dermatitis. We conclude that GBP-1 expression is closely associated with skin lesions in patients with CLE, suggesting a contribution of GBP-1 in the pathogenesis of this disease.

Current and emerging strategies for the treatment and management of systemic lupus erythematosus based on molecular signatures of acute and chronic inflammation

Lupus is a chronic, systemic inflammatory condition in which eicosanoids, cytokines, nitric oxide (NO), a deranged immune system, and genetics play a significant role. Our studies revealed that an imbalance in the pro- and antioxidants and NO and an alteration in the metabolism of essential fatty acids exist in lupus. The current strategy of management includes administration of nonsteroidal anti-inflammatory drugs such as hydroxychloroquine and immunosuppressive drugs such as corticosteroids. Investigational drugs include the following: 1) belimumab, a fully human monoclonal antibody that specifically recognizes and inhibits the biological activity of B-lymphocyte stimulator, also known as B-cell-activation factor of the TNF family; 2) stem cell transplantation; 3) rituximab, a chimeric monoclonal antibody against CD20, which is primarily found on the surface of B-cells and can therefore destroy B-cells; and 4) IL-27, which has potent anti-inflammatory actions. Our studies showed that a regimen of corticosteroids and cyclophosphamide, and methods designed to enhance endothelial NO synthesis and augment antioxidant defenses, led to induction of long-lasting remission of the disease. These results suggest that methods designed to modulate molecular signatures of the disease process and suppress inflammation could be of significant benefit in lupus. Some of these strategies could be vagal nerve stimulation, glucose-insulin infusion, and administration of lipoxins, resolvins, protectins, and nitrolipids by themselves or their stable synthetic analogs that are known to suppress inflammation and help in the resolution and healing of the inflammation-induced damage. These strategies are likely to be useful not only in lupus but also in other conditions, such as rheumatoid arthritis, scleroderma, ischemia-reperfusion injury to the myocardium, ischemic heart disease, and sepsis.

Elevated plasma level of HMGB1 is associated with disease activity and combined alterations with IFN-α and TNF-α in systemic lupus erythematosus

Recent studies indicate that high-mobility group box protein 1 (HMGB1) contributes to the pathogenesis of diverse autoimmune disorders. It induces the production of interferon-alpha (IFN-alpha) and tumor necrosis factor alpha (TNF-alpha) in vitro. In the present study, plasma HMGB1, TNF-alpha, and IFN-alpha were determined with ELISA in 37 patients with systemic lupus erythematosus (SLE) and 39 age- and sex-matched healthy controls (HC). The possible associations of these cytokines with disease activities, autoantibodies, and certain laboratory parameters were also explored. The plasma levels of HMGB1, TNF-alpha, and IFN-alpha were increased in SLE patients compared with those of HC (P < 0.05). Moreover, the levels of HMGB1 and TNF-alpha in the active SLE patients were elevated compared with those in inactive patients and HC. Additionally, plasma HMGB1 was positively correlated with peripheral neutrophils, and plasma TNF-alpha was positively correlated with anti-Sm, ESR and CRP, while plasma IFN-alpha was inversely correlated with the age and platelet level in SLE patients. Our data indicated that increased plasma HMGB1 was associated with disease activity in SLE, which was similar to TNF-alpha. High level of plasma IFN-alpha may be related to nephritis and thrombocytopenia in SLE.

Autoimmune skin inflammation is dependent on plasmacytoid dendritic cell activation by nucleic acids via TLR7 and TLR9

Lupus-prone mice develop a chronic inflammatory response to cutaneous injury that depends on the production of type I interferon, TLR7, and TLR9.

Recognition of endogenous DNA and RNA by cells expressing TLR7 and TLR9 is an important contributor to the pathogenesis of systemic lupus erythematosus and has been suggested to contribute to cutaneous lupus and to a group of related inflammatory skin diseases termed interface dermatitis. We have developed a mouse model of TLR7- and TLR9-dependent skin inflammation using tape stripping. In normal mice, this resulted in a rapid but transient inflammatory cell infiltration accompanied by induction of type I IFN production by plasmacytoid dendritic cells (PDCs) and release of extracellular traps and proinflammatory cytokines by neutrophils. These responses were strongly reduced in MyD88-deficient mice and in mice treated with a bifunctional inhibitor of TLR7 and TLR9. In contrast, in lupus-prone (NZBxNZW)F₁ mice, tape stripping induced the development of chronic lesions characterized by a persistent type I IFN gene signature and many clinical and histological features of cutaneous lupus. Depletion of PDCs before injury prevented the development of skin lesions, whereas treatment with a bifunctional TLR7/9 inhibitor before tape stripping or after the initial lesion was established led to a significant reduction of the disease. These data suggest that inhibitors of TLR7 and TLR9 signaling have potential therapeutic application for the treatment of interface dermatitis.

Cutaneous lupus erythematosus: recent lessons from animal models

Cutaneous lupus erythematosus (CLE) may present as a clinically heterogeneous group of lupus-specific skin lesions that have common histopathological findings. Determination of the immunopathological sequence of events in this group of disorders has been challenging for dermatologists and immunologists but is vital for therapeutic targeting. We review animal models in which different aspects of immune alteration in CLE have been addressed. The MRL/lpr mouse develops spontaneous skin disease with some features of CLE. Study of this strain and related gene-manipulated strains has revealed roles for multiple cytokines, including interleukin (IL)-6, IL-18, and IL-21, in disease pathogenesis. A role for the growth factor colony stimulating factor 1 and the inflammatory protein high-mobility group box 1 has also been suggested. We discuss potential novel treatment options suggested by these models.

Transplantation of umbilical cord mesenchymal stem cells alleviates lupus nephritis in MRL/lpr mice

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease, which, despite the advances in immunosuppressive medical therapies, remains potentially fatal in some patients, especially in treatment-refractory patients. This study found that transplantation of umbilical cord mesenchymal stem cells (UC-MSCs) has the same therapeutic effect as transplantation of bone marrow mesenchymal stem cells (BM-MSCs), which has been reported to be efficient in treating SLE-related symptoms in MRL/lpr mice. Multi-treatment (at the 18th, 19th, and 20th weeks of age) of 1 × 10(6) UC-MSCs was able to decrease the levels of 24-h proteinuria, serum creatinine, and anti-double-stranded DNA (dsDNA) antibody, and the extent of renal injury such as crescent formation in MRL/lpr mice. A lower, but still significant, reduction in these parameters was also observed in mice receiving a single dose of UC-MSCs (at the 18th week). UC-MSCs treatment also inhibited expression of monocyte chemotactic protein-1 (MCP-1) and high-mobility group box 1 (HMGB-1) expression in a similar fashion. UC-MSCs labeled with carboxyfluorescein diacetate succinimidyl ester (CFSE) were found in the lungs and kidneys 1 week post infusion. In addition, after 11 weeks post UC-MSCs infusion, human cells were found in kidney of UC-MSCs-treated mice. These findings indicated that UC-MSCs transplantation might be a potentially promising approach in the treatment of lupus nephritis, possibly by inhibiting MCP-1 and HMGB-1 production.

DAMPening inflammation by modulating TLR signalling

Damage-associated molecular patterns (DAMPs) include endogenous intracellular molecules released by activated or necrotic cells and extracellular matrix (ECM) molecules that are upregulated upon injury or degraded following tissue damage. DAMPs are vital danger signals that alert our immune system to tissue damage upon both infectious and sterile insult. DAMP activation of Toll-like receptors (TLRs) induces inflammatory gene expression to mediate tissue repair. However, DAMPs have also been implicated in diseases where excessive inflammation plays a key role in pathogenesis, including rheumatoid arthritis (RA), cancer, and atherosclerosis. TLR activation by DAMPs may initiate positive feedback loops where increasing tissue damage perpetuates pro-inflammatory responses leading to chronic inflammation. Here we explore the current knowledge about distinct signalling cascades resulting from self TLR activation. We also discuss the involvement of endogenous TLR activators in disease and highlight how specifically targeting DAMPs may yield therapies that do not globally suppress the immune system.

HMGB1 in systemic lupus Erythematosus: Its role in cutaneous lesions development

The chromatin non-histone DNA binding protein high mobility group box one (HMGB1) has recently been extensively studied in autoimmune diseases. In addition to its nuclear functions, HMGB1 has been identified as alarmin that can 'alarm' both innate and adaptive immunity. HMGB1 can amplify inflammation and enhance immune responses by interacting with the receptor for Advanced Glycation End Products (RAGE) and Toll-like receptors 2,4 and 9 (TLRs) . Release of HMGB1 occurs during cell activation as well as cell death. Cells die by apoptosis and eventually necrosis which both are thought to lead to release of HMGB1 into the microenvironment. In the past years disturbed apoptosis or clearance of apoptotic cells has been put forward as a major pathophysiological feature in autoimmune diseases such as Systemic Lupus Erythematosus (SLE), which is a prototypic autoimmune disease that affects many organs. Accumulation of apoptotic cells has been found in SLE. Also, elevated levels of HMGB1 have been detected in the serum of SLE patients and increased expression of HMGB1 was demonstrated in skin lesions of lupus patients. In this review the general characteristics and activities of HMGB1 are highlighted and its role in SLE will be discussed with special attention to its involvement in the pathogenesis of skin lesions.

Nucleic acid sensing receptors in systemic lupus erythematosus: development of novel DNA- and/or RNA-like analogues for treating lupus

Double-stranded (ds) DNA, DNA- or RNA-associated nucleoproteins are the primary autoimmune targets in SLE, yet their relative inability to trigger similar autoimmune responses in experimental animals has fascinated scientists for decades. While many cellular proteins bind non-specifically negatively charged nucleic acids, it was discovered only recently that several intracellular proteins are involved directly in innate recognition of exogenous DNA or RNA, or cytosol-residing DNA or RNA viruses. Thus, endosomal Toll-like receptors (TLR) mediate responses to double-stranded RNA (TLR-3), single-stranded RNA (TLR-7/8) or unmethylated bacterial cytosine (phosphodiester) guanine (CpG)-DNA (TLR-9), while DNA-dependent activator of IRFs/Z-DNA binding protein 1 (DAI/ZBP1), haematopoietic IFN-inducible nuclear protein-200 (p202), absent in melanoma 2 (AIM2), RNA polymerase III, retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) mediate responses to cytosolic dsDNA or dsRNA, respectively. TLR-induced responses are more robust than those induced by cytosolic DNA- or RNA- sensors, the later usually being limited to interferon regulatory factor 3 (IRF3)-dependent type I interferon (IFN) induction and nuclear factor (NF)-kappaB activation. Interestingly, AIM2 is not capable of inducing type I IFN, but rather plays a role in caspase I activation. DNA- or RNA-like synthetic inhibitory oligonucleotides (INH-ODN) have been developed that antagonize TLR-7- and/or TLR-9-induced activation in autoimmune B cells and in type I IFN-producing dendritic cells at low nanomolar concentrations. It is not known whether these INH-ODNs have any agonistic or antagonistic effects on cytosolic DNA or RNA sensors. While this remains to be determined in the future, in vivo studies have already shown their potential for preventing spontaneous lupus in various animal models of lupus. Several groups are exploring the possibility of translating these INH-ODNs into human therapeutics for treating SLE and bacterial DNA-induced sepsis.

The alarmin functions of high-mobility group proteins

High-mobility group (HMG) proteins are non-histone nuclear proteins that bind nucleosomes and regulate chromosome architecture and gene transcription. Over the past decade, numerous studies have established that some HMG proteins can be released extracellularly and demonstrate distinct extracellular biological activities. Here, we will give a brief overview of HMG proteins and highlight their participation in innate/inflammatory and adaptive immune responses. They have the activities of alarmins, which are endogenous mediators that are rapidly released in response to danger signals initiated by infection and/or tissue damage and are capable of activating innate and adaptive immunity by promoting the recruitment and activation of antigen-presenting cells (APCs).

RAGE-independent autoreactive B cell activation in response to chromatin and HMGB1/DNA immune complexes

Increasing evidence suggests that the excessive accumulation of apoptotic or necrotic cellular debris may contribute to the pathology of systemic autoimmune disease. HMGB1 is a nuclear DNA-associated protein, which can be released from dying cells thereby triggering inflammatory processes. We have previously shown that IgG2a-reactive B cell receptor (BCR) transgenic AM14 B cells proliferate in response to endogenous chromatin immune complexes (ICs), in the form of the anti-nucleosome antibody PL2-3 and cell debris, in a TLR9-dependent manner, and that these ICs contain HMGB1. Activation of AM14 B cells by these chromatin ICs was inhibited by a soluble form of the HMGB1 receptor, RAGE-Fc, suggesting HMGB1-RAGE interaction was important for this response. To further explore the role of HMGB1 in autoreactive B cell activation, we assessed the capacity of purified calf thymus HMGB1 to bind dsDNA fragments and found that HMGB1 bound both CG-rich and CG-poor DNA. However, HMGB1-DNA complexes could not activate AM14 B cells unless HMGB1 was bound by IgG2a and thereby able to engage the BCR. To ascertain the role of RAGE in autoreactive B cell responses to chromatin ICs, we intercrossed AM14 and RAGE-deficient mice. We found that spontaneous and defined DNA ICs activated RAGE+ and RAGE(- ) AM14 B cells to a comparable extent. These results suggest that HMGB1 promotes B cell responses to endogenous TLR9 ligands through a RAGE-independent mechanism.

Expression of high-mobility group box 1 and of receptor for advanced glycation end products in chronic obstructive pulmonary disease

RATIONALE

Chronic obstructive pulmonary disease (COPD) is characterized by airway inflammation and remodeling. High-mobility group box 1 (HMGB1), a nuclear protein that is released during inflammation and repair, interacts with proinflammatory cytokines and with the receptor for advanced glycation end products (RAGE), which is highly expressed in the lung.

OBJECTIVES

To determine whether HMGB1 is augmented in COPD and is associated with IL-1beta and RAGE.

METHODS

HMGB1 was assessed in the bronchoalveolar lavage (BAL) of 20 never-smokers, 20 smokers, and 30 smokers with COPD and it was correlated with inflammatory and clinical parameters. In parallel, HMGB1 and RAGE immunolocalization was determined in bronchial and lung tissues. Last, binding of HMGB1 to IL-1beta in human macrophages and in BAL fluid was examined.

MEASUREMENTS AND MAIN RESULTS

BAL levels of HMGB1 were higher in smokers with COPD than in smokers and never-smokers (P < 0.0001 for both comparisons), and similar differences were observed in epithelial cells and alveolar macrophages. BAL HMGB1 correlated positively with IL-1beta (r(s) = 0.438; P = 0.0006) and negatively with FEV(1) (r(s) = -0.570; P < 0.0001) and transfer factor of the lung for carbon monoxide (r(s) = -0.382; P = 0.0026). HMGB1-IL-1beta complexes were found in BAL supernatant and alveolar macrophages from smokers and patients with COPD, as well as in the human macrophage cell line, THP-1, where they enhanced the synthesis of tumor-necrosis factor-alpha. RAGE was overexpressed in the airway epithelium and smooth muscle of patients with COPD and it colocalized with HMGB1.

CONCLUSIONS

Elevated HMGB1 expression in COPD airways may sustain inflammation and remodeling through its interaction with IL-1beta and RAGE.

Expression of high mobility group box chromosomal protein 1 and its modulating effects on downstream cytokines in systemic lupus erythematosus

OBJECTIVE

To compare the expression of high mobility group box chromosomal protein 1 (HMGB1) and the modulating effects on its downstream cytokines in patients with systemic lupus erythematosus (SLE) and healthy controls.

METHODS

HMGB1 concentrations in serum from SLE patients and controls were measured by immunoblot analysis. HMGB1 messenger RNA (mRNA) expression in peripheral blood mononuclear cells (PBMC) was detected by real-time reverse transcription-polymerase chain reaction. Immunofluorescence assay was employed to examine the translocation of HMGB1 in monocytes after endotoxin stimulation. Release of tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6) by PBMC after rHMGB1 stimulation was also measured.

RESULTS

Serum HMGB1 levels and HMGB1 mRNA expressions in PBMC were elevated in SLE patients compared with controls. A positive correlation was demonstrated between HMGB1 concentrations and SLE Disease Activity Index. There was an inverse correlation between HMGB1 levels and C4 and C3 concentrations in SLE patients. HMGB1 concentrations were higher in patients with vasculitis and myositis. Lipopolysaccharide stimulated a temporarily elevated release of HMGB1 in SLE patients compared with controls. The pattern and localization of HMGB1 staining in monocytes were similar in both groups. After stimulation with rHMGB1, TNF-alpha level decreased but IL-6 level increased in SLE patients compared with controls.

CONCLUSION

Our findings suggest that increased serum levels of HMGB1 in SLE may be associated with lupus disease activity. The altered production of TNF-alpha and IL-6 in response to rHMGB1 stimulation may participate in the disruption of cytokine homeostasis in SLE.

Effects of HMGB1 on in vitro responses of isolated muscle fibers and functional aspects in skeletal muscles of idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are heterogeneous rheumatic disorders of unknown cause characterized by muscle weakness, inflammatory cell infiltrates, and major histocompatibility complex (MHC) class I expression on muscle fibers. The nonhistone nuclear protein alarmin high-mobility group box 1 protein (HMGB1) has been detected extranuclearly in muscle biopsies from patients with IIMs. We hypothesize that HMGB1 has a central role in the cause of muscle weakness, particularly in the early phases of IIMs. Experiments were performed on skeletal muscle fibers isolated from adult mice, which were exposed to recombinant interferon (IFN)-gamma or HMGB1. The myoplasmic free [Ca(2+)] was measured. Stimulation with IFN-gamma resulted in increased HMGB1 expression in muscle nuclei and the myoplasm. Exposure to HMGB1 induced a reversible up-regulation of MHC class I in the muscle fibers. However, HMGB1 exposure caused an irreversible decrease in Ca(2+) release from the sarcoplasmic reticulum during fatigue, induced by repeated tetanic contractions. HMGB1 and MHC class I were frequently colocalized in the myoplasm of muscle fibers in muscle biopsies from patients with early IIMs. However, HMGB1-expressing fibers outnumbered fibers expressing MHC class I. Our data indicate that HMGB1 could be an early inducer of skeletal muscle dysfunction in IIMs.

A clear and present danger: endogenous ligands of Toll-like receptors

Neurologic disease promoted by microbial pathogens, sterile injury, or neurodegeneration rapidly induces innate immunity in adjacent healthy tissue, which in turn contributes extensively to neurologic injury. With more recent focus on innate immune processes, it appears that necrotic, but not apoptotic, death mechanisms provoke inflammatory responses likely due to the release or production of endogenous ligands that activate resident immune cells of the central nervous system. These ligands comprise a diverse set of proteins, nucleic acids, and glycosaminoglycans, including heat shock proteins, HMGB1, RNA, DNA, hyaluronan, and heparin sulfate, that stimulate innate immune mechanisms largely through Toll-like receptors (TLRs). The blockade of interactions between endogenous ligands and TLRs may enable neuroprotective therapeutic strategies for a variety of neurologic diseases.

Association of HMGB1 polymorphisms with outcome after allogeneic hematopoietic cell transplantation

Several studies have demonstrated that genetic variation in cytokine genes can modulate the immune reactions after allogeneic hematopoietic cell transplantation (HCT). High mobility group box 1 protein (HMBG1) is a pleiotropic cytokine that functions as a pro-inflammatory signal, important for the activation of antigen presenting cells (APCs) and propagation of inflammation. HMGB1 is implicated in the pathophysiology of a variety of inflammatory diseases, and we have recently found the variation in the HMGB1 gene to be associated with mortality in patients with systemic inflammatory response syndrome. To assess the impact of the genetic variation in HMGB1 on outcome after allogeneic HCT, we genotyped 276 and 146 patient/donor pairs treated with allogeneic HCT for hematologic malignancies following myeloablative (MA) or nonmyeloablative (NMA) conditioning. Associations between genotypes and outcome were only observed in the cohort treated with MA conditioning. Patient homozygosity or heterozygosity for the-1377delA minor allele was associated with increased risk of relapse (hazard ratio [HR] 2.11, P = .02) and increased relapse related mortality (RRM) (P = .03). Furthermore, patient homozygosity for the 3814C > G minor allele was associated with increased overall survival (OS; HR 0.13, P = .04), progression free survival (PFS; HR 0.30, P = .05) and decreased probability of RRM (P = .03). Patient carriage of the 2351insT minor allele reduced the risk of grade II to IV acute graft-versus-host disease (aGVHD) (HR 0.60, P = .01), whereas donor homozygosity was associated with chronic GVHD (cGVHD) (HR 1.54, P = .01). Our findings suggest that the inherited variation in HMGB1 is associated with outcome after allogeneic HCT following MA conditioning. None of the polymorphisms were associated with treatment-related mortality (TRM).

Endogenous damage-associated molecular pattern molecules at the crossroads of inflammation and cancer

Inflammatory mediators play important roles in the development and progression of cancer. Cellular stress, damage, inflammation, and necrotic cell death cause release of endogenous damage-associated molecular pattern (DAMP) molecules or alarmins, which alert the host of danger by triggering immune responses and activating repair mechanisms through their interaction with pattern recognition receptors. Recent studies show that abnormal persistence of these molecules in chronic inflammation and in tumor microenvironments underlies carcinogenesis and tumor progression, indicating that DAMP molecules and their receptors could provide novel targets for therapy. This review focuses on the role of DAMP molecules high-mobility group box 1 and S100 proteins in inflammation, tumor growth, and early metastatic events.

Dendritic cells as danger-recognizing biosensors

Dendritic cells (DCs) are antigen presenting cells that are characterized by a potent capacity to initiate immune responses. DCs comprise several subsets with distinct phenotypes. After sensing any danger(s) to the host via their innate immune receptors such as Toll-like receptors, DCs become mature and subsequently present antigens to CD4⁺ T cells. Since DCs possess the intrinsic capacity to polarize CD4⁺ helper cells, it is critical to understand the immunological roles of DCs for clinical applications. Here, we review the different DC subsets, their danger-sensing receptors and immunological functions. Furthermore, the cytokine reporter mouse model for studying DC activation is introduced.

Lupus antibodies to the HMGB1 chromosomal protein: epitope mapping and association with disease activity

The high mobility group box 1 (HMGB1) protein is a non-histone chromosomal protein that acts as a potent proinflammatory cytokine when actively secreted from LPS- or TNF-activated macrophages, monocytes, and other cells. Anti-HMGB1/2 antibodies have been previously identified in sera from a high proportion of patients with autoimmune diseases. In this study, we examined anti-HMGB1 antibody titers in sera of patients with systemic rheumatic diseases and the correlations between the presence of anti-HMGB1 antibodies and disease activity in systemic lupus erythematosus (SLE) patients by enzyme-linked immunosorbent assay and western blotting. We detected increases in both the levels and the frequency of anti-HMGB1 antibodies in sera from SLE and polymyositis/dermatomyositis (PM/DM) patients, and observed that the presence of anti-HMGB1 antibodies positively correlates with SLE disease activity index. Through epitope mapping, we found that multiple HMGB1 epitopes were recognised in SLE sera, with the major epitope mapping to box A. Another epitope, the joiner region of HMGB1, was preferentially recognized by SLE sera, but not by PM/DM sera. Collectively, these observations suggest that the presence of anti-HMGB1 antibodies correlates with disease activity in SLE patients.

Induction of inflammatory and immune responses by HMGB1-nucleosome complexes: implications for the pathogenesis of SLE

Autoantibodies against double-stranded DNA (dsDNA) and nucleosomes represent a hallmark of systemic lupus erythematosus (SLE). However, the mechanisms involved in breaking the immunological tolerance against these poorly immunogenic nuclear components are not fully understood. Impaired phagocytosis of apoptotic cells with consecutive release of nuclear antigens may contribute to the immune pathogenesis. The architectural chromosomal protein and proinflammatory mediator high mobility group box protein 1 (HMGB1) is tightly attached to the chromatin of apoptotic cells. We demonstrate that HMGB1 remains bound to nucleosomes released from late apoptotic cells in vitro. HMGB1–nucleosome complexes were also detected in plasma from SLE patients. HMGB1-containing nucleosomes from apoptotic cells induced secretion of interleukin (IL) 1β, IL-6, IL-10, and tumor necrosis factor (TNF) α and expression of costimulatory molecules in macrophages and dendritic cells (DC), respectively. Neither HMGB1-free nucleosomes from viable cells nor nucleosomes from apoptotic cells lacking HMGB1 induced cytokine production or DC activation. HMGB1-containing nucleosomes from apoptotic cells induced anti-dsDNA and antihistone IgG responses in a Toll-like receptor (TLR) 2–dependent manner, whereas nucleosomes from living cells did not. In conclusion, HMGB1–nucleosome complexes activate antigen presenting cells and, thereby, may crucially contribute to the pathogenesis of SLE via breaking the immunological tolerance against nucleosomes/dsDNA.

Evidence for a pathogenetic role of interleukin-18 in cutaneous lupus erythematosus

OBJECTIVE

Cutaneous manifestations are the most common clinical features of lupus erythematosus (LE). The aim of this study was to analyze differences in the inflammatory response of keratinocytes from patients with cutaneous LE (CLE) compared with healthy controls.

METHODS

Keratinocytes from LE patients and controls were cultured from epidermal stem cells of the hair follicle of anagen head hairs. Functional responses of keratinocytes to cytokine stimulation were determined by flow cytometry and enzyme-linked immunosorbent assay. Biopsy samples of lesional skin were analyzed by immunohistochemistry.

RESULTS

Keratinocytes from CLE patients expressed higher levels of IL-18 receptor on their cell surface in response to tumor necrosis factor alpha (TNFalpha) or interferon-gamma stimulation. In response to IL-18 stimulation, these cells produced large amounts of TNFalpha. Of note, in the presence of IL-18, CLE keratinocytes failed to express IL-12. IL-12 has previously been shown to protect keratinocytes from ultraviolet irradiation-induced apoptosis. Keratinocytes from LE patients were more prone to die upon exposure to IL-18, and this increased apoptosis was abrogated by blockade of endogenously produced TNFalpha as well as by the addition of exogenous IL-12. IL-18 was highly expressed in biopsy samples of lesional skin from CLE patients.

CONCLUSION

Our results demonstrate an intrinsic difference in the inflammatory response of keratinocytes and indicate an autocrine feedback loop involving TNFalpha, IL-18, and IL-12 family members. Our results suggest that IL-18 may occupy an important position in the cytokine hierarchy in CLE, indicating the potential benefit of a local agent that blocks IL-18 activity in the treatment of the manifestations of CLE.

High mobility group box 1 protein inhibits the proliferation of human mesenchymal stem cells and promotes their migration and differentiation along osteoblastic pathway

Extracellular high mobility group box 1 (HMGB1) is a novel cytokine that takes part in the processes of inflammation, tissue damage and regeneration. Mesenchymal stem cells (MSCs) are adult stem cells characterized by their inherently suppressive activities on inflammative and allo-immune reactions. In the present study, we have addressed whether HMGB1 could affect the biological properties of human bone marrow MSCs. Transwell experiments showed that HMGB1 induced MSC migration and this effect could not be hampered by a blocking antibody against the receptor for advanced glycation end products (RAGE). MSCs exposed to HMGB1 were negative for CD31, CD45, CD80, and HLA-DR, and displayed equal levels of CD73, CD166, and HLA-ABC compared with their counterparts, but HMGB1 profoundly suppressed MSC proliferation in a dose-dependent manner as evaluated by carboxyfluorescein diacetate succinmidyl ester dye dilution assay. Furthermore, HMGB1 triggered the differentiation of MSCs into osteoblasts as identified by histochemical staining, traditional RT-PCR and real-time RT-PCR analysis on mRNA expression of lineage-specific molecular markers. The differentiation-inductive activity could neither be inhibited by RAGE neutralizing antibody. Moreover, HMGB1-treated MSCs displayed unchanged suppressive activity on in vitro lymphocyte cell proliferation elicited by ConA. Collectively, the data suggest that MSCs are a target of HMGB1.