Macrophages in obesity are characterised by increased IL-1ß response to calcium-sensing receptor signals.

OBJECTIVE: Obesity is complicated by inflammatory activation of the innate immune system. Stimulation of the calcium-sensing receptor (CaSR) by extra-cellular calcium ions ([Ca2+]ex) can trigger NLRP3 inflammasome activation and inflammation. We hypothesised, that this mechanism might contribute to the activation of adipose tissue (AT) in obesity, and investigated [Ca2+]ex-induced, CaSR mediated IL-1ß release by macrophages in obesity. METHODS: [Ca2+]ex-induced IL-1ß release was investigated in monocyte-derived macrophages (MDM) generated from peripheral blood of patients with obesity and from normal-weight controls. Visceral and subcutaneous AT biosamples were stimulated with [Ca2+]ex, and IL-1ß release, as well as expression of NLRP3 inflammasome and cytokine genes, was determined. RESULTS: Both MDM and AT readily responded with concentration-dependent IL-1ß release already at low, near physiological concentrations to addition of [Ca2+]ex, which was more than 80 fold higher than the LPS-induced effect. IL-1ß levels induced by [Ca2+]ex were significantly higher not only in MDM from patients with obesity compared to controls, but also in visceral versus subcutaneous AT. This fat-depot difference was also reflected by mRNA expression levels of inflammasome and cytokine genes. CONCLUSIONS: Obesity renders macrophages more susceptible to [Ca2+]ex-induced IL-1ß release and pyroptosis. Increased susceptibility was independent of the response to LPS and circulating CRP arguing against mere pro-inflammatory pre-activation of monocytes. Instead, we propose that CaSR mediated signalling is relevant for the deleterious innate immune activation in obesity.

In vitro response pattern of monocytes after tmTNF reverse signaling predicts response to anti-TNF therapy in rheumatoid arthritis.

BACKGROUND: Treatment with TNF inhibitors is very efficient in the majority of the patients with rheumatoid arthritis (RA), but it does not achieve a sufficient treatment response in 40-50% of the cases. Goal of the study was to assess functional ex vivo-tests of RA monocytes as prognostic parameters of the subsequent treatment response. METHODS: 20 anti-TNF naïve RA patients were enrolled in a prospective, open-label trial, and Etanercept therapy was initiated. Prior to treatment, reverse signaling was induced in peripheral blood monocytes by tmTNF crosslinking via TNFR2:Ig construct Etanercept in a standardized ex vivo-assay. Released cytokine and cytokine receptor concentrations were determined as parameters of the monocyte response. RESULTS: Crosslinking of tmTNF and consecutive reverse signaling led to production of pro- and anti-inflammatory cytokines and of soluble cytokine decoy receptors such as sTNFR1 and sIL-1R2. Several of the measured concentrations were found to correlate with the treatment response according to the EULAR criteria. The correlation was most pronounced in sTNFR1 concentrations (r = -0.657, p = 0.0031), which also predicted a good clinical response with the highest sensitivity and specificity according to EULAR criteria. CONCLUSIONS: Herein we propose that the tmTNF crosslinking-triggered shedding of soluble decoy receptors and production of anti-inflammatory cytokines could contribute to the clinical efficacy of TNF inhibitors, and that in vitro quantification of this secretion by RA monocytes prior to treatment can be used to predict the clinical response. Further development of such standardized tests could be a step towards personalized medicine by providing rheumatologists with a rational choice for first line biological therapy in patients with RA.

Brief report: deficient thymic output in rheumatoid arthritis despite abundance of prethymic progenitors.

OBJECTIVE: To determine the frequencies of common lymphoid progenitors (CLPs) and recent thymic emigrants (RTEs) in patients with rheumatoid arthritis (RA) and healthy control subjects. METHODS: Flow cytometry was performed to determine the frequencies of CLPs and RTEs in the peripheral blood of 101 control subjects and 51 patients with RA. Thirteen of these patients were also analyzed longitudinally for 6 months after initiation of treatment with a tumor necrosis factor (TNF) inhibitor. RESULTS: A significant correlation between the frequencies of CLPs and RTEs was observed in healthy control subjects. The frequencies of both CLPs and RTEs decreased with age and correlated inversely with absolute lymphocyte numbers in peripheral blood. In patients with RA, the frequencies of RTEs were significantly decreased compared with the frequencies in control subjects. Importantly, the frequencies of CLPs were significantly higher in patients with RA compared with control subjects. Therapeutic TNF blockade further increased the frequency of CLPs, thereby normalizing thymic output, as indicated by an increase in the number of RTEs. CONCLUSION: Thymic insufficiency in RA is not attributable to an inadequate supply of progenitor cells to the thymus. Thus, insufficient numbers of RTEs could result from inadequate thymic T cell neogenesis, or alternatively, could be a consequence of high CD4+ T cell turnover, homeostatic proliferation, and subsequent dilution of the RTE population.

Tumor necrosis factor receptor type I expression of CD4+ T cells in rheumatoid arthritis enables them to follow tumor necrosis factor gradients into the rheumatoid synovium.

OBJECTIVE: The cytokine tumor necrosis factor (TNF) plays a central role in the pathogenesis of rheumatoid arthritis (RA), but its disease-specific effector mechanisms have not been fully elucidated. This study was undertaken to investigate the role of TNF in T cell accumulation and migration in the synovitic joints of RA patients. METHODS: Vital tissue sections from rheumatoid synovium were generated using a horizontally oscillating microtome and were coincubated with fluorescence-labeled CD4+ T cells. Migration was detected by fluorescence and confocal microscopy. Migrating T cells were recovered from the tissue and analyzed for phenotype. Chemotaxis of CD4+ T cells from RA patients in response to increasing concentrations of TNF was analyzed in Transwell experiments. RESULTS: CD4+ T cells from RA patients migrated into the tissue sections in significantly higher numbers than T cells from healthy controls. Migrating CD4+ T cells differed from nonmigrating ones in their increased expression of TNF receptor type I (TNFRI), which was expressed on a fraction of circulating CD4+ T cells from RA patients, but not from controls. CD4+ T cells from the peripheral blood of RA patients were also found to migrate along TNF concentration gradients ex vivo. Accordingly, blockade of either TNF or TNFRI nearly abrogated in vitro T cell migration in synovial tissue. CONCLUSION: Our findings indicate that the interaction of TNF with TNFRI is pivotal for T cell migration in synovial tissue in vitro, and thereby suggest a relevant role of the cytokine for in vivo T cell trafficking to synovitic joints.

Triclosan and its alternatives, especially chlorhexidine, modulate macrophage immune response with distinct modes of action.

Since European regulators restricted the use of bacteriocidic triclosan (TCS), alternatives for TCS are emerging. Recently, TCS has been shown to reprogram immune metabolism, trigger the NLRP3 inflammasome, and subsequently the release of IL-1ß in human macrophages, but data on substitutes is scarce. Hence, we aimed to examine the effects of TCS compared to its alternatives at the molecular level in human macrophages. LPS-stimulated THP-1 macrophages were exposed to TCS or its substitutes, including benzalkonium chloride, benzethonium chloride, chloroxylenol, chlorhexidine (CHX) and cetylpyridinium chloride, with the inhibitory concentration (IC10-value) of cell viability to decipher their mode of action. TCS induced the release of the pro-inflammatory cytokine TNF and high level of IL-1ß, suggesting the activation of the NLRP3-inflammasome, which was confirmed by non-apparent IL-1ß under the NLRP3-inhibitor MCC950 treatment d. While IL-6 release was reduced in all treatments, the alternative CHX completely abolished the release of all investigated cytokines. To unravel the underlying molecular mechanisms, we used untargeted LC-MS/MS-based proteomics. TCS and CHX showed the strongest cellular response at the protein and signalling pathway level, whereby pathways related to metabolism, translation, cellular stress and migration were mainly affected but to different proposed modes of action. TCS inhibited mitochondrial electron transfer and affected phagocytosis. In contrast, in CHX-treated cells, the translation was arrested due to stress conditions, resulting in the formation of stress granules. Mitochondrial (e.g. ATP5F1D, ATP5PB, UQCRQ) and ribosomal (e.g. RPL10, RPL35, RPS23) proteins were revealed as putative key drivers. Furthermore, we have demonstrated the formation of podosomes by CHX, potentially involved in ECM degradation. Our results exhibit modulation of the immune response in macrophages by TCS and its substitutes and illuminated underlying molecular effects. These results illustrate critical processes involved in the modulation of macrophages' immune response by TCS and its alternatives, providing information essential for hazard assessment.

The CD14(bright) CD16+ monocyte subset is expanded in rheumatoid arthritis and promotes expansion of the Th17 cell population.

OBJECTIVE: Circulating monocytes contain a subpopulation of CD14+CD16+ cells; this subpopulation of cells has been described to be proinflammatory and to have an increased frequency in rheumatoid arthritis (RA). New evidence suggests that this subpopulation can be further subdivided into CD14(dim) CD16+ and CD14(bright) CD16+ cells. The aim of this study was to determine which of the two CD16+ monocyte subpopulations is expanded in patients with RA and to investigate their possible role in disease pathogenesis. METHODS: The frequencies of monocyte subpopulations in the peripheral blood of healthy donors and patients with RA were determined by flow cytometry. Monocyte subpopulations were sorted and cocultured with CD4+ T cells. Cytokines were determined in the supernatant, and Th17 cell frequencies were measured by flow cytometry. RESULTS: In comparison with the other monocyte subpopulations, CD14(bright) CD16+ cells showed higher HLA-DR and CCR5 expression and responded with higher tumor necrosis factor production to direct cell contact with preactivated T cells. They were observed at increased frequencies in the peripheral blood of patients with RA, while CD14(dim) CD16+ monocyte frequencies were not increased. CD14(bright) CD16+ cells were extremely potent inducers of Th17 cell expansion in vitro. Their frequency in the peripheral blood of patients with RA correlated closely with Th17 cell frequencies determined ex vivo. CONCLUSION: This study is the first to provide a link between the increased frequency of the CD14(bright) CD16+ monocyte subpopulation in RA and the expansion of Th17 cells, which are likely to have a role in the pathogenesis of autoimmunity.

Association of anticytomegalovirus seropositivity with more severe joint destruction and more frequent joint surgery in rheumatoid arthritis.

OBJECTIVE: Expansion of autoreactive CD4+CD28(null) T cells is associated with extraarticular disease manifestations, including rheumatoid vasculitis, and it has recently been demonstrated that expansion of these T cells is associated with anticytomegalovirus (anti-CMV) seropositivity. This study was undertaken to investigate a possible link between latent CMV infection and rheumatoid arthritis (RA). METHODS: In a retrospective analysis, anti-CMV antibodies and clinical, serologic, and radiologic parameters of joint destruction were examined in 202 RA patients and 272 healthy controls. In addition, frequencies of CD4+CD28(null) T cells; concentrations of the cytokines monocyte chemotactic protein 1 (MCP-1), interferon-α (IFNα), and IFN-inducible protein 10; and anti-CMV-specific T cell responses were analyzed in RA patients. RESULTS: Overall, no significant difference in the frequency of anti-CMV seropositivity between RA patients and healthy controls was observed. Among individuals older than age 55 years, however, anti-CMV IgG antibodies were significantly more frequent in RA patients than controls (65.3% and 54.7%, respectively; P = 0.05). Anti-CMV seropositivity in RA patients was associated with an increased frequency of CD4+CD28(null) T cells and increased serum concentrations of MCP-1. The frequency of anti-CMV-specific CD4+ T cells producing IFNγ was increased in RA patients compared to controls. Most importantly, anti-CMV-seropositive RA patients showed radiographic evidence of more advanced joint destruction and had increased frequencies of joint-related surgical procedures, indicating more severe joint disease. CONCLUSION: Our findings indicate that latent CMV infection aggravates the clinical course of RA and is associated with increased frequencies of CD4+CD28(null) T cells and of CMV-specific IFNγ-secreting CD4+ T cells.

LPS-induced cytokine production in human monocytes and macrophages.

Lipopolysaccharide (LPS) from Gram-negative bacteria is one of the most potent innate immune-activating stimuli known. Here we review the current understanding of LPS effects on human monocyte and macrophage function. We provide an overview of LPS signal transduction with attention given to receptor cooperativity and species differences in LPS responses, as well as the role of tyrosine phosphorylation and lysine acetylation in signalling. We also review LPS-regulated transcription, with emphasis on chromatin remodeling and primary versus secondary transcriptional control mechanisms. Finally, we review the regulation and function of LPS-inducible cytokines produced by human monocytes and macrophages including TNFα, the IL-1 family, IL-6, IL-8, the IL-10 family, the IL-12 family, IL-15 and TGFß.

Danger signal extracellular calcium initiates differentiation of monocytes into SPP1/osteopontin-producing macrophages.

The danger signal extracellular calcium is pathophysiologically increased in the synovial fluid of patients with rheumatoid arthritis (RA). Calcium activates the NLRP3-inflammasome via the calcium-sensing receptor in monocytes/macrophages primed by lipopolysaccharide, and this effect is mediated by the uptake of calciprotein particles (CPPs) formed out of calcium, phosphate, and fetuin-A. Aim of the study was to unravel the influence of calcium on monocytes when the priming signal is not present. Monocytes were isolated from the blood of healthy controls and RA patients. Macrophages were characterized using scRNA-seq, DNA microarray, and proteomics. Imaging flow cytometry was utilized to study intracellular events. Here we show that extracellular calcium and CPPs lead to the differentiation of monocytes into calcium-macrophages when the priming signal is absent. Additional growth factors are not needed, and differentiation is triggered by calcium-dependent CPP-uptake, lysosomal alkalization due to CPP overload, and TFEB- and STAT3-dependent increased transcription of the lysosomal gene network. Calcium-macrophages have a needle-like shape, are characterized by excessive, constitutive SPP1/osteopontin production and a strong pro-inflammatory cytokine response. Calcium-macrophages differentiated out of RA monocytes show a stronger manifestation of this phenotype, suggesting the differentiation process might lead to the pro-inflammatory macrophage response seen in the RA synovial membrane.

Cytokine-induced human IFN-gamma-secreting effector-memory Th cells in chronic autoimmune inflammation.

T-helper (Th) cells activated by cytokines in the absence of T-cell receptor ligation are suspected to participate in inflammatory processes by production of interferon-gamma (IFN-gamma). Still, the relevance of such a mechanism has not been addressed in humans. Here we demonstrate that a subset of human effector-memory Th cells expressing functional interleukin-12R (IL-12R), IL-18Ralpha, and CCR5 ex vivo can be induced to secrete IFN-gamma by cytokines signaling via the IL-2R common gamma-chain in combination with IL-12 and IL-18. Cytokine-driven IFN-gamma production depends on JAK3- and p38 mitogen-activated kinase signals and is sensitive to suppression by CD25(++) regulatory T cells. Contrary to IFN-gamma(+) Th cells induced upon antigen-specific stimulation, their cytokine-activated counterparts characteristically lack expression of costimulator 4-1BB (CD137). Strikingly, the majority of Th cells infiltrating inflamed joints of rheumatoid arthritis patients is equipped with receptors prerequisite for cytokine-induced IFN-gamma secretion. Among these cells, we detected a substantial fraction that secretes IFN-gamma directly ex vivo but lacks 4-1BB expression, indicating that cytokine-induced IFN-gamma(+) Th cells operate in autoimmune inflammation. Our data provide a rationale for how human effector-memory Thcells can participate in perpetuating inflammatory processes in autoimmunity even in the absence of T-cell receptor ligation.

Herpesvirus entry mediator-Ig treatment during immunization aggravates rheumatoid arthritis in the collagen-induced arthritis model.

Previous studies attempting to influence the severity of collagen-induced arthritis (CIA) by modulating the LIGHT (lymphotoxin-related inducible ligand that competes for glycoprotein D binding to herpesvirus entry mediator (HVEM) on T cells)/lymphotoxin pathway have yielded conflicting results. To further clarify the role of LIGHT in autoimmune arthritis, a HVEM-Ig fusion protein was used. CIA was induced in DBA1 mice, which were injected i.p. with recombinant HVEM-Ig fusion protein and control Ig at different time points. Severity of clinical arthritis and histologic joint destruction were significantly increased in HVEM-Ig-treated mice compared with control-Ig-treated mice. Collagen II-induced in vitro T cell proliferation and IFN-gamma production was augmented in mice treated with HVEM-Ig, as was the production of IgG2a anti-collagen II Ab. Accordingly, serum concentrations of IFN-gamma and IL-6 were higher in mice treated with HVEM-Ig. In conclusion, HVEM-Ig aggravates autoimmunity in collagen-induced arthritis, which is possibly mediated by interaction with B and T lymphocyte attenuator (BTLA) or CD160, despite the blockade of LIGHT. Hence, HVEM-Ig seems not to be a valid therapeutic option in autoimmune arthritis.

Clonal expansions in selected TCR BV families of rheumatoid arthritis patients are reduced by treatment with the TNFα inhibitors etanercept and infliximab.

Clonal expansions of autoreactive CD4+ T cells are frequently present in patients with rheumatoid arthritis (RA) and are stable over long periods of time. This study was undertaken to investigate the influence of anti-TNFα treatment on such clonal expansions in the peripheral CD4+ T-cell compartment. TNFα inhibiting therapies significantly reduced the total number of expanded clonotypes. This effect was mainly observed in clonal expansions in the BV6 family, while in clonal expansions of the BV14 family no such effect was seen. No change in the percentage of CD4+ CD28 null T cells was observed. Serum concentrations of the pro-homeostatic cytokine IL-7 were found to increase in patients responding TNFα-inhibiting therapy. These data argue for a normalization of adaptive immune mechanisms under TNFα inhibiting therapies, which may be secondary to the control of inflammation but contribute to the efficacy of cytokine blockade therapy.

Calcium-sensing receptor-mediated NLRP3 inflammasome response to calciprotein particles drives inflammation in rheumatoid arthritis.

Increased extracellular Ca2+ concentrations ([Ca2+]ex) trigger activation of the NLRP3 inflammasome in monocytes through calcium-sensing receptor (CaSR). To prevent extraosseous calcification in vivo, the serum protein fetuin-A stabilizes calcium and phosphate into 70-100 nm-sized colloidal calciprotein particles (CPPs). Here we show that monocytes engulf CPPs via macropinocytosis, and this process is strictly dependent on CaSR signaling triggered by increases in [Ca2+]ex. Enhanced macropinocytosis of CPPs results in increased lysosomal activity, NLRP3 inflammasome activation, and IL-1ß release. Monocytes in the context of rheumatoid arthritis (RA) exhibit increased CPP uptake and IL-1ß release in response to CaSR signaling. CaSR expression in these monocytes and local [Ca2+] in afflicted joints are increased, probably contributing to this enhanced response. We propose that CaSR-mediated NLRP3 inflammasome activation contributes to inflammatory arthritis and systemic inflammation not only in RA, but possibly also in other inflammatory conditions. Inhibition of CaSR-mediated CPP uptake might be a therapeutic approach to treating RA.

Perturbation of the Monocyte Compartment in Human Obesity.

Circulating monocytes can be divided into classical (CM), intermediate (IM), and non-classical monocytes (NCM), and the classical monocytes also contain CD56+ monocytes and monocytic myeloid-derived suppressor cells (M-MDSC). The aim of the study was to evaluate the occurrence of the monocyte subpopulations in human obesity. Twenty-seven normal, 23 overweight, and 60 obese individuals (including 17 obese individuals with normal glucose tolerance and 27 with type 2 diabetes) were included into this study. Peripheral blood mononuclear cells were isolated from human blood, and surface markers to identify monocyte subpopulations were analyzed by flow cytometry. Obese individuals had higher numbers of total monocytes, CM, IM, CD56+ monocytes, and M-MDSCs. The number of CM, IM, CD56+ monocytes, and M-MDSCs, correlated positively with body mass index, body fat, waist circumference, triglycerides, C-reactive protein, and HbA1c, and negatively with high-density lipoprotein cholesterol. Individuals with obesity and type 2 diabetes had higher numbers of IM, NCM, and M-MDSCs, whereas those with obesity and impaired glucose tolerance had higher numbers of CD56+ monocytes. In summary, the comprehensive analysis of blood monocytes in human obesity revealed a shift of the monocyte compartment toward pro-inflammatory monocytes which might contribute to the development of low-grade inflammation in obesity, and immune-suppressive monocytes which might contribute to the development of cancer in obesity.

The role of α7nAChR in controlling the anti-inflammatory/anti-arthritic action of galantamine.

OBJECTIVE: The evolution of the "cholinergic anti-inflammatory pathway" and the fact that the α 7 subunit of the nicotinic acetylcholine receptor (α7nAChR) is present in the spleen, joint and on the surface of lymphocytes, opened up the prospective in this study of targeting the α7nAChR by the anticholinesterase and cholinergic drug, galantamine, to control inflammation in rheumatoid arthritis (RA). METHODS: Twelve-adjuvant arthritic rats were exposed to the selective α7nAChR blocker methylcaconitine citrate 15 min before galantamine treatment. As control, six adjuvant arthritic rats were treated with galantamine and six others were untreated. After five days TNF-α levels were assessed in spleen and joints, while reduced glutathione was measured in blood and joint tissue. In the second part, magnetically sorted CD4 + T cells from peripheral blood mononuclear cells of RA patients and healthy donors were used to sort CD4 + CD25 - primary T cells (Tresp) and CD4 + CD25 + CD127low Tregs. The suppressive function of Tregs was investigated after incubation with galantamine using flow cytometry. Cell culture supernatants were analyzed for TNF-α and IL-10 levels after three days incubation period of Tregs with Tresp. The effect of galantamine on Tregs was then blocked by α-Bungarotoxin and the same assay has been repeated. RESULTS & CONCLUSION: Selective α7nAChR blockade interrupted the anti-inflammatory effect of galantamine in the spleen and joints of arthritic rats. In healthy donors, galantamine could strengthen the suppressive activity of Tregs; while in RA patients it did not modulate the function of Tregs significantly. Further studies are necessary to investigate whether modulation of the cholinergic nervous system, especially α7nAChR, could have impact on the disturbed immune system in RA, which may open up a new treatment option of autoimmune diseases.

Fatty Acid Oxidation Compensates for Lipopolysaccharide-Induced Warburg Effect in Glucose-Deprived Monocytes.

Monocytes enter sites of microbial or sterile inflammation as the first line of defense of the immune system and initiate pro-inflammatory effector mechanisms. We show that activation with bacterial lipopolysaccharide (LPS) induces them to undergo a metabolic shift toward aerobic glycolysis, similar to the Warburg effect observed in cancer cells. At sites of inflammation, however, glucose concentrations are often drastically decreased, which prompted us to study monocyte function under conditions of glucose deprivation and abrogated Warburg effect. Experiments using the Seahorse Extracellular Flux Analyzer revealed that limited glucose supply shifts monocyte metabolism toward oxidative phosphorylation, fueled largely by fatty acid oxidation at the expense of lipid droplets. While this metabolic state appears to provide sufficient energy to sustain functional properties like cytokine secretion, migration, and phagocytosis, it cannot prevent a rise in the AMP/ATP ratio and a decreased respiratory burst. The molecular trigger mediating the metabolic shift and the functional consequences is activation of AMP-activated protein kinase (AMPK). Taken together, our results indicate that monocytes are sufficiently metabolically flexible to perform pro-inflammatory functions at sites of inflammation despite glucose deprivation and inhibition of the LPS-induced Warburg effect. AMPK seems to play a pivotal role in orchestrating these processes during glucose deprivation in monocytes.

Latent Cytomegalovirus Infection in Rheumatoid Arthritis and Increased Frequencies of Cytolytic LIR-1+CD8+ T Cells.

OBJECTIVE: Leukocyte immunoglobulin-like receptor 1 (LIR-1) is up-regulated by cytomegalovirus (CMV), which in turn, has been associated with premature aging and more severe joint disease in patients with rheumatoid arthritis (RA). The aim of this study was to investigate the expression and functional significance of LIR-1 in CMV-positive RA patients. METHODS: We determined the phenotype, cytolytic potential, CMV-specific proliferation, and HLA-G-triggered, LIR-1-mediated inhibition of interferon-γ secretion of LIR-1+ T cells in RA patients and healthy controls. RESULTS: We found increased frequencies of CD8+ T cells with CMV pp65-specific T cell receptors in CMV-positive RA patients as compared to CMV-positive healthy controls. CMV-specific CD8+ T cells in these patients were preferentially LIR-1+ and exhibited a terminally differentiated polyfunctional phenotype. The numbers of LIR-1+CD8+ T cells increased with age and disease activity, and showed high levels of reactivity to CMV antigens. Ligation of LIR-1 with soluble HLA-G molecules in vitro confirmed an inhibitory role of the molecule when expressed on CD8+ T cells in RA patients. CONCLUSION: We propose that latent CMV infection in the context of a chronic autoimmune response induces the recently described "chronic infection phenotype" in CD8+ T cells, which retains anti-infectious effector features while exhibiting autoreactive cytolytic potential. This response is likely dampened by LIR-1 to avoid overwhelming immunopathologic changes in the setting of the autoimmune disease RA. The known deficiency of soluble HLA-G in RA and the observed association of LIR-1 expression with disease activity suggest, however, that LIR-1+ T cells are insufficiently controlled in RA and are still likely to be involved in the pathogenesis of the disease.

GPRC6A mediates Alum-induced Nlrp3 inflammasome activation but limits Th2 type antibody responses.

Alum adjuvanticity is still an unknown mechanism despite the frequent use as vaccine adjuvant in humans. Here we show that Alum-induced inflammasome activation in vitro and in vivo is mediated by the G protein-coupled receptor GPRC6A. The Alum-induced humoral response in vivo was independent of the inflammasome because Nlrp3-/- and ASC-/- mice responded normally to Alum and blockade of IL-1 had no effect on antibody production. In contrast, Alum adjuvanticity was increased in GPRC6A-/- mice resulting in increased antibody responses and increased Th2 cytokine concentrations compared to wildtype mice. In vitro activation of GPRC6A-/- splenic B cells also induced increased IgG1 concentrations compared to wildtype B cells. For the first time, we show GPRC6A expression in B cells, contributing to the direct effects of Alum on those cells. B cell produced immunostimulatory IL-10 is elevated in GPRC6A-/- B cells in vitro and in vivo. Our results demonstrate a dual role of GPRC6A in Alum adjuvanticity. GPCR6A activation by Alum leads to the initiation of innate inflammatory responses whereas it is an important signal for the limitation of adaptive immune responses induced by Alum, partially explained by B cell IL-10.

Brief Report: Autocrine Cytokine-Mediated Deficiency of TRAIL-Induced Monocyte Apoptosis in Rheumatoid Arthritis.

OBJECTIVE: Dysregulated apoptosis of monocytes is a pathogenic feature of rheumatoid arthritis (RA). The aim of this study was to investigate the role of TRAIL and TRAIL-induced apoptosis in patients with RA. METHODS: Cell surface expression and serum concentrations of TRAIL were determined in 63 patients with RA, and TRAIL-induced monocyte apoptosis was quantified. Surface expression of TRAILR-1, TRAILR-2, TRAILR-3, TRAILR-4, CXCR1, and CXCR2 was determined, and intracellular signal transduction was investigated. In 8 patients with RA, clinical and laboratory parameters of disease activity were investigated longitudinally, before and after initiation of treatment with tumor necrosis factor (TNF) inhibitors. RESULTS: Serum concentrations of both TRAIL and interleukin-8 (IL-8) were increased in patients with RA, while cell surface expression of the TRAIL receptors TRAILR-1, TRAILR-2, TRAILR-3, and TRAILR-4 was diminished. TRAIL-induced monocyte apoptosis was significantly decreased in RA due to increased TRAIL-induced IL-8 secretion by RA monocytes. The combined effect of TRAIL and IL-8 on monocytes resulted in activation of antiapoptotic pathways, including p42/44 MAPK and p38. Susceptibility to TRAIL-induced apoptosis was restored in RA monocytes after 3 months of TNF inhibition. CONCLUSION: In RA, circulating monocytes with the potential to produce proinflammatory cytokines appear to have defects in several pathways of apoptosis induction, among which is a deficiency in TRAIL-induced apoptosis. Although this resistance to apoptosis might contribute to perpetuation of the disease, it remains to be determined whether specific induction of apoptosis could be therapeutically beneficial.