Association between IL-6 production in synovial explants from rheumatoid arthritis patients and clinical and imaging response to biologic treatment: A pilot study.

INTRODUCTION: The need for biomarkers which can predict disease course and treatment response in rheumatoid arthritis (RA) is evident. We explored whether clinical and imaging responses to biologic disease modifying anti-rheumatic drug treatment (bDMARD) were associated with the individual's mediator production in explants obtained at baseline. METHODS: RA Patients were evaluated by disease activity score 28 joint C-reactive protein (DAS 28-)), colour Doppler ultrasound (CDUS) and 3 Tesla RA magnetic resonance imaging scores (RAMRIS). Explants were established from synovectomies from a needle arthroscopic procedure prior to initiation of bDMARD. Explants were incubated with the bDMARD in question, and the productions of interleukin-6 (IL-6), monocyte chemo-attractive protein-1 (MCP-1) and macrophage inflammatory protein-1-beta (MIP-1b) were measured by multiplex immunoassays. The changes in clinical and imaging variables following a minimum of 3 months bDMARD treatment were compared to the baseline explant results. Mixed models and Spearman's rank correlations were performed. P-values below 0.05 were considered statistically significant. RESULTS: 16 patients were included. IL-6 production in bDMARD-treated explants was significantly higher among clinical non-responders compared to responders (P = 0.04), and a lack of suppression of IL-6 by the bDMARDS correlated to a high DAS-28 (ρ = 0.57, P = 0.03), CDUS (ρ = 0.53, P = 0.04) and bone marrow oedema (ρ = 0.56, P = 0.03) at follow-up. No clinical association was found with explant MCP-1 production. MIP-1b could not be assessed due to a large number of samples below the detection limit. CONCLUSIONS: Synovial explants appear to deliver a disease-relevant output testing which when carried out in advance of bDMARD treatment can potentially pave the road for a more patient tailored treatment approach with better treatment effects.

Sp1 phosphorylation by ATM downregulates BER and promotes cell elimination in response to persistent DNA damage.

ATM (ataxia-telangiectasia mutated) is a central molecule for DNA quality control. Its activation by DNA damage promotes cell-cycle delay, which facilitates DNA repair prior to replication. On the other hand, persistent DNA damage has been implicated in ATM-dependent cell death via apoptosis; however, the mechanisms underlying this process remain elusive. Here we find that, in response to persistent DNA strand breaks, ATM phosphorylates transcription factor Sp1 and initiates its degradation. We show that Sp1 controls expression of the key base excision repair gene XRCC1, essential for DNA strand break repair. Therefore, degradation of Sp1 leads to a vicious cycle that involves suppression of DNA repair and further aggravation of the load of DNA damage. This activates transcription of pro-apoptotic genes and renders cells susceptible to elimination via both apoptosis and natural killer cells. These findings constitute a previously unrecognized 'gatekeeper' function of ATM as a detector of cells with persistent DNA damage.

Inhibition of histone H3K27 demethylases selectively modulates inflammatory phenotypes of natural killer cells.

Natural killer (NK) cells are innate lymphocytes, important in immune surveillance and elimination of stressed, transformed, or virus-infected cells. They critically shape the inflammatory cytokine environment to orchestrate interactions of cells of the innate and adaptive immune systems. Some studies have reported that NK cell activation and cytokine secretion are controlled epigenetically but have yielded only limited insight into the mechanisms. Using chemical screening with small-molecule inhibitors of chromatin methylation and acetylation, further validated by knockdown approaches, we here identified Jumonji-type histone H3K27 demethylases as key regulators of cytokine production in human NK cell subsets. The prototypic JMJD3/UTX (Jumonji domain-containing protein 3) H3K27 demethylase inhibitor GSK-J4 increased global levels of the repressive H3K27me3 mark around transcription start sites of effector cytokine genes. Moreover, GSK-J4 reduced IFN-γ, TNFα, granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukin-10 levels in cytokine-stimulated NK cells while sparing their cytotoxic killing activity against cancer cells. The anti-inflammatory effect of GSK-J4 in NK cell subsets, isolated from peripheral blood or tissue from individuals with rheumatoid arthritis (RA), coupled with an inhibitory effect on formation of bone-resorbing osteoclasts, suggested that histone demethylase inhibition has broad utility for modulating immune and inflammatory responses. Overall, our results indicate that H3K27me3 is a dynamic and important epigenetic modification during NK cell activation and that JMJD3/UTX-driven H3K27 demethylation is critical for NK cell function.

Interleukin-15-activated natural killer cells kill autologous osteoclasts via LFA-1, DNAM-1 and TRAIL, and inhibit osteoclast-mediated bone erosion in vitro.

Osteoclasts reside on bone and are the main bone resorbing cells playing an important role in bone homeostasis, while natural killer (NK) cells are bone-marrow-derived cells known to play a crucial role in immune defence against viral infections. Although mature NK cells traffic through bone marrow as well as to inflammatory sites associated with enhanced bone erosion, including the joints of patients with rheumatoid arthritis, little is known about the impact NK cells may have on mature osteoclasts and bone erosion. We studied the interaction between human NK cells and autologous monocyte-derived osteoclasts from healthy donors in vitro. We show that osteoclasts express numerous ligands for receptors present on activated NK cells. Co-culture experiments revealed that interleukin-15-activated, but not resting, NK cells trigger osteoclast apoptosis in a dose-dependent manner, resulting in drastically decreased bone erosion. Suppression of bone erosion requires contact between NK cells and osteoclasts, but soluble factors also play a minor role. Antibodies masking leucocyte function-associated antigen-1, DNAX accessory molecule-1 or tumour necrosis factor-related apoptosis-inducing ligand enhance osteoclast survival when co-cultured with activated NK cells and restore the capacity of osteoclasts to erode bone. These results suggest that interleukin-15-activated NK cells may directly affect bone erosion under physiological and pathological conditions.

Synovial explant inflammatory mediator production corresponds to rheumatoid arthritis imaging hallmarks: a cross-sectional study.

INTRODUCTION: Despite the widespread use of magnetic resonance imaging (MRI) and Doppler ultrasound for the detection of rheumatoid arthritis (RA) disease activity, little is known regarding the association of imaging-detected activity and synovial pathology. The purpose of this study was to compare site-specific release of inflammatory mediators and evaluate the corresponding anatomical sites by examining colour Doppler ultrasound (CDUS) and MRI scans. METHODS: RA patients were evaluated on the basis of CDUS and 3-T MRI scans and subsequently underwent synovectomy using a needle arthroscopic procedure of the hand joints. The synovial tissue specimens were incubated for 72 hours, and spontaneous release of monocyte chemoattractant protein 1 (MCP-1), interleukin 6 (IL-6), macrophage inflammatory protein 1ß (MIP-1ß) and IL-8 was measured by performing multiplex immunoassays. Bone marrow oedema (BME), synovitis and erosion scores were estimated on the basis of the rheumatoid arthritis magnetic resonance imaging score (RAMRIS). Mixed models were used for the statistical analyses. Parsimony was achieved by omitting covariates with P > 0.1 from the statistical model. RESULTS: Tissue samples from 58 synovial sites were obtained from 25 patients. MCP-1 was associated with CDUS activity (P = 0.009, approximate Spearman's ρ = 0.41), RAMRIS BME score (P = 0.01, approximate Spearman's ρ = 0.42) and RAMRIS erosion score (P = 0.03, approximate Spearman's ρ = 0.31). IL-6 was associated with RAMRIS synovitis score (P = 0.04, approximate Spearman's ρ = 0.50), BME score (P = 0.04, approximate Spearman's ρ = 0.31) and RAMRIS erosion score (P = 0.03, approximate Spearman's ρ = 0.35). MIP-1ß was associated with CDUS activity (P = 0.02, approximate Spearman's ρ = 0.38) and RAMRIS synovitis scores (P = 0.02, approximate Spearman's ρ = 0.63). IL-8 associations with imaging outcome measures did not reach statistical significance. CONCLUSIONS: The association between imaging activity and synovial inflammatory mediators underscores the high sensitivity of CDUS and MRI in the evaluation of RA disease activity. The associations found in our present study have different implications for synovial mediator releases and corresponding imaging signs. For example, MCP-1 and IL-6 were associated with both general inflammation and bone destruction, in contrast to MIP-1ß, which was involved solely in general synovitis. The lack of association of IL-8 with synovitis was likely underestimated because of a large proportion of samples above assay detection limits among the patients with the highest synovitis scores.

Balance between activating NKG2D, DNAM-1, NKp44 and NKp46 and inhibitory CD94/NKG2A receptors determine natural killer degranulation towards rheumatoid arthritis synovial fibroblasts.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation and synovial hyperplasia leading to progressive joint destruction. Fibroblast-like synoviocytes (FLS) are central components of the aggressive, tumour-like synovial structure termed pannus, which invades the joint space and cartilage. A distinct natural killer (NK) cell subset expressing the inhibitory CD94/NKG2A receptor is present in RA synovial fluid. Little is known about possible cellular interactions between RA-FLS and NK cells. We used cultured RA-FLS and the human NK cell line Nishi, of which the latter expresses an NK receptor repertoire similar to that of NK cells in RA synovial fluid, as an in vitro model system of RA-FLS/NK cell cross-talk. We show that RA-FLS express numerous ligands for both activating and inhibitory NK cell receptors, and stimulate degranulation of Nishi cells. We found that NKG2D, DNAM-1, NKp46 and NKp44 are the key activating receptors involved in Nishi cell degranulation towards RA-FLS. Moreover, blockade of the interaction between CD94/NKG2A and its ligand HLA-E expressed on RA-FLS further enhanced Nishi cell degranulation in co-culture with RA-FLS. Using cultured RA-FLS and the human NK cell line Nishi as an in vitro model system of RA-FLS/NK cell cross-talk, our results suggest that cell-mediated cytotoxicity of RA-FLS may be one mechanism by which NK cells influence local joint inflammation in RA.

T(H)1, T(H)2, and T(H)17 cells instruct monocytes to differentiate into specialized dendritic cell subsets.

Monocytes and T helper (T(H)) cells rapidly infiltrate inflamed tissues where monocytes differentiate into inflammatory dendritic cells (DCs) through undefined mechanisms. Our studies indicate that T(H) cells frequently interact with monocytes in inflamed skin and elicit the differentiation of specialized DC subsets characteristic of these lesions. In psoriasis lesions, T(H)1 and T(H)17 cells interact with monocytes and instruct these cells to differentiate into T(H)1- and T(H)17-promoting DCs, respectively. Correspondingly, in acute atopic dermatitis, T(H)2 cells interact with monocytes and elicit the formation of T(H)2-promoting DCs. DC formation requires GM-CSF and cell contact, whereas T(H) subset specific cytokines dictate DC function and the expression of DC subset specific surface molecules. Moreover, the phenotypes of T cell-induced DC subsets are maintained after subsequent stimulation with a panel of TLR agonists, suggesting that T(H)-derived signals outweigh downstream TLR signals in their influence on DC function. These findings indicate that T(H) cells govern the formation and function of specialized DC subsets.

Natural killer cells trigger osteoclastogenesis and bone destruction in arthritis.

Osteoclasts are bone-eroding cells that develop from monocytic precursor cells in the presence of receptor activator of NF-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Osteoclasts are essential for physiological bone remodeling, but localized excessive osteoclast activity is responsible for the periarticular bone destruction that characteristically occurs in patients with rheumatoid arthritis (RA). The origin of osteoclasts at sites of bone erosion in RA is unknown. Natural killer (NK) cells, as well as monocytes, are abundant in the inflamed joints of patients with RA. We show here that such NK cells express both RANKL and M-CSF and are frequently associated with CD14(+) monocytes in the RA synovium. Moreover, when synovial NK cells are cocultured with monocytes in vitro, they trigger their differentiation into osteoclasts, a process dependent on RANKL and M-CSF. As in RA, NK cells in the joints of mice with collagen-induced arthritis (CIA) express RANKL. Depletion of NK cells from mice before the induction of CIA reduces the severity of subsequent arthritis and almost completely prevents bone erosion. These results suggest that NK cells may play an important role in the destruction of bone associated with inflammatory arthritis.

Qa-1(b)-dependent modulation of dendritic cell and NK cell cross-talk in vivo.

Dendritic cells (DC) trigger activation and IFN-gamma release by NK cells in lymphoid tissues, a process important for the polarization of Th1 responses. Little is known about the molecular signals that regulate DC-induced NK cell IFN-gamma synthesis. In this study, we analyzed whether the interaction between Qa-1(b) expressed on DC and its CD94/NKG2A receptor on NK cells affects this process. Activation of DC using CpG-oligodeoxynucleotides in Qa-1(b)-deficient mice, or transfer of CpG-oligodeoxynucleotide-activated Qa-1(b)-deficient DC into wild-type mice, resulted in dramatically increased IFN-gamma production by NK cells, as compared with that induced by Qa-1(b)-expressing DC. Masking the CD94/NKG2A inhibitory receptor on NK cells in wild-type mice similarly enhanced the IFN-gamma response of these cells to Qa-1(b)-expressing DC. Furthermore, NK cells from CD94/NKG2A-deficient mice displayed higher IFN-gamma production upon DC stimulation. These results demonstrate that Qa-1(b) is critically involved in regulating IFN-gamma synthesis by NK cells in vivo through its interaction with CD94/NKG2A inhibitory receptors. This receptor-ligand interaction may be essential to prevent unabated cytokine production by NK cells during an inflammatory response.

CD101 surface expression discriminates potency among murine FoxP3+ regulatory T cells.

CD4+CD25+FoxP3+ regulatory T cells (Treg) have been shown to be protective in animal models of autoimmunity and acute graft-vs-host disease. However, owing to the functional heterogeneity among CD4+CD25+ T cells, surface markers expressed selectively on functionally active Treg would be useful for purposes of identifying and isolating such cells. We generated a rabbit mAb against murine CD101, a transmembrane glycoprotein involved in T cell activation. Among freshly isolated T cells, CD101 was detected on 25-30% of CD4+CD25+ Treg and approximately 20% of conventional memory T cells. CD101(high) Treg displayed greater in vitro suppression of alloantigen-driven T cell proliferation as compared with CD101(low) Treg. In a model of graft-vs-host disease induced by allogeneic bone marrow transplantation in vivo bioluminescence imaging demonstrated reduced expansion of donor-derived luciferase-labeled conventional T cells in mice treated with CD101(high) Treg, compared with CD101(low) Treg. Moreover, treatment with CD101(high) Treg resulted in improved survival, reduced proinflammatory cytokine levels and reduced end organ damage. Among the CD101(high) Treg all of the in vivo suppressor activity was contained within the CD62L(high) subpopulation. We conclude that CD101 expression distinguishes murine Treg with potent suppressor activity.

Natural killer cells trigger differentiation of monocytes into dendritic cells.

Circulating monocytes can differentiate into dendritic cells (moDCs), which are potent inducers of adaptive immune responses. Previous reports show that granulocyte macrophage-colony-stimulating factor (GM-CSF) and interleukin-4 induce monocyte differentiation into moDCs in vitro, but little is known about the physiological requirements that initiate moDC differentiation in vivo. Here we show that a unique natural killer (NK) cell subset (CD3(-)CD56(bright)) that accumulates in lymph nodes and chronically inflamed tissues triggers CD14(+) monocytes to differentiate into potent T-helper-1 (T(H)1) promoting DC. This process requires direct contact of monocytes with NK cells and is mediated by GM-CSF and CD154 derived from NK cells. It is noteworthy that synovial fluid (SF) from patients with rheumatoid arthritis (RA) and psoriatic arthritis (PsA), but not osteoarthritis (OA), induces monocytes to differentiate into DC. However, this process occurs only in the presence of NK cells. We propose that NK cells play a role in the maintenance of T(H)1-mediated inflammatory diseases such as RA by providing a local milieu for monocytes to differentiate into DC.

Activating and inhibitory receptors on synovial fluid natural killer cells of arthritis patients: role of CD94/NKG2A in control of cytokine secretion.

Natural killer (NK) cells are activated early during inflammatory events and contribute to the shaping of the ensuing adaptive immune response. To further understand the role for NK cells in inflammation, we investigated the phenotype and function of synovial fluid (SF) NK cells from patients with chronic joint inflammation, as well as from patients with transient inflammation of the knee following trauma. We confirm that synovial NK cells are similar to the well-characterized CD56(bright) peripheral blood (PB) NK-cell subset present in healthy individuals. However, compared to this PB subset the synovial NK cells express a higher degree of activation markers including CD69 and NKp44, the latter being up-regulated also on CD56(bright) NK cells in the PB of patients. Activated synovial NK cells produced interferon-gamma and tumour necrosis factor, and the production was further up-regulated by antibody masking of CD94/NKG2A, and down-regulated by target cells expressing human leucocyte antigen-E in complex with peptides known to engage CD94/NKG2A. We conclude that synovial NK cells have an activated phenotype and that CD94/NKG2A is a key regulator of synovial NK-cell cytokine synthesis.

A signal peptide derived from hsp60 binds HLA-E and interferes with CD94/NKG2A recognition.

Human histocompatibility leukocyte antigen (HLA)-E is a nonclassical major histocompatibility complex (MHC) class I molecule which presents a restricted set of nonameric peptides, derived mainly from the signal sequence of other MHC class I molecules. It interacts with CD94/NKG2 receptors expressed on the surface of natural killer (NK) cells and T cell subsets. Here we demonstrate that HLA-E also presents a peptide derived from the leader sequence of human heat shock protein 60 (hsp60). This peptide gains access to HLA-E intracellularly, resulting in up-regulated HLA-E/hsp60 signal peptide cell-surface levels on stressed cells. Notably, HLA-E molecules in complex with the hsp60 signal peptide are no longer recognized by CD94/NKG2A inhibitory receptors. Thus, during cellular stress an increased proportion of HLA-E molecules may bind the nonprotective hsp60 signal peptide, leading to a reduced capacity to inhibit a major NK cell population. Such stress induced peptide interference would gradually uncouple CD94/NKG2A inhibitory recognition and provide a mechanism for NK cells to detect stressed cells in a peptide-dependent manner.

IFN-gamma protects short-term ovarian carcinoma cell lines from CTL lysis via a CD94/NKG2A-dependent mechanism.

IFN-gamma regulates the immunogenicity of target cells by increasing their expression of HLA class I molecules. This facilitates the T cell receptor-mediated recognition by CD8(+) T cells but decreases target cell sensitivity to lysis by NK cells due to engagement of inhibitory NK receptors. In this study, short-term tumor cell lines from patients with advanced ovarian carcinomas were established. We demonstrate the paradoxical finding that IFN-gamma treatment of these short-term ovarian carcinoma cell lines (OVACs) resulted in resistance of tumor cells to lysis by peptide- and allospecific CD8(+) T cells. Blocking experiments revealed that this phenomenon was dependent on enhanced inhibitory signalling via CD94/NKG2A receptors expressed on the effector cells. This was associated with increased expression of HLA-E mRNA and HLA-G at the protein level in IFN-gamma-treated OVACs. Furthermore, pulsing of untreated OVACs with the leader sequence peptide of HLA-G protected these cells from lysis by CTLs, thus mimicking the inhibitory effect of IFN-gamma. This study provides evidence that CD94/NKG2A receptors play an important role in regulating T cell activity against tumors and shows that IFN-gamma modulation of target cells may shift the balance of triggering and inhibitory signals to T cells, turning off their cytolytic activity.