Macrophage activation and inflammatory priming by anti-MAA antibodies in rheumatoid arthritis.

We studied the effects of rheumatoid arthritis (RA) autoantibodies that target malondialdehyde-acetaldehyde protein adducts (anti-MAA) on inflammation and macrophage functions. We detected a profound reprogramming of gene expressions and the production of chemokines, such as CCL22 and CCL24, in anti-MAA exposed macrophages. Moreover, anti-MAA pretreatment promoted a more inflammatory cytokine profile upon TLR activation. Although anti-MAA are typically multi-reactive, we observed a prominent clonal diversity in inducing macrophage activation. Anti-MAA antibodies were not arthritogenic in mice, but altered a set of cytokine and growth factor encoding genes in the joints. In individuals at risk of RA anti-MAA IgG levels correlated with circulating inflammatory mediators prior to and at arthritis onset. Certain IgG anti-MAA clones may thus contribute to an inflammatory priming of the joint prior to the onset of systemic inflammation via inducing FcγR-mediated macrophage pre-activation and setting the stage for augmented responses to subsequent inflammatory stimuli.

Identification of early risk factors for anti-citrullinated-protein-antibody positive rheumatoid arthritis-a prospective cohort study.

OBJECTIVE: Individuals positive for anti-cyclic-peptide-antibodies (anti-CCP) and musculoskeletal complaints (MSK-C) are at risk for developing rheumatoid arthritis (RA). In this study we aimed to investigate factors involved in arthritis progression. METHODS: Anti-CCP2-positive individuals with MSK-C referred to a rheumatologist were recruited. Individuals lacked arthritis at clinical and ultrasound examination and were followed for ≥three years or until clinical arthritis diagnosis. Blood samples from inclusion were analyzed for; nine anti-citrullinated-protein-antibody (ACPA) reactivities (citrullinated α-1-enolase, fibrinogen, filaggrin, histone, vimentin and tenascin peptides); 92 inflammation-associated proteins; and HLA-shared epitope alleles. Cox regression was applied to the data to identify independent predictors in a model. RESULTS: 267 individuals were included with median follow up of 49 months (IQR: 22-60). 101 (38%) developed arthritis after median 14 months (IQR: 6-27). The analysis identified that presence of at least one ACPA reactivity (HR 8.0, 95% CI 2.9-22), ultrasound detected tenosynovitis (HR 3.4, 95% CI 2.0-6.0), IL6 levels (HR 1.5, 95% CI 1.2-1.8) and IL15-Rα levels (HR 0.6, 95% CI 0.4-0.9) are significant independent predictors for arthritis progression in a prediction model (Harrell's C 0.76 [SE 0.02], AUC 0.82 [95% CI 0.76-0.89], cross-validated AUC 0.70 [95% CI 0.56-0.85]). CONCLUSION: We propose a high-Risk-RA phase characterized by presence of ACPA reactivity, tenosynovitis, IL6, and IL15-Rα and suggest that these factors need to be further investigated for their biological effects and clinical values, to identify individuals at particular low risk and high risk for arthritis progression.

The human bone marrow plasma cell compartment in rheumatoid arthritis - Clonal relationships and anti-citrulline autoantibody producing cells.

A majority of circulating IgG is produced by plasma cells residing in the bone marrow (BM). Long-lived BM plasma cells constitute our humoral immune memory and are essential for infection-specific immunity. They may also provide a reservoir of potentially pathogenic autoantibodies, including rheumatoid arthritis (RA)-associated anti-citrullinated protein autoantibodies (ACPA). Here we investigated paired human BM plasma cell and peripheral blood (PB) B-cell repertoires in seropositive RA, four ACPA+ RA patients and one ACPA- using two different single-cell approaches, flow cytometry sorting, and transcriptomics, followed by recombinant antibody generation. Immunoglobulin (Ig) analysis of >900 paired heavy-light chains from BM plasma cells identified by either surface CD138 expression or transcriptome profiles (including gene expression of MZB1, JCHAIN and XBP1) demonstrated differences in IgG/A repertoires and N-linked glycosylation between patients. For three patients, we identified clonotypes shared between BM plasma cells and PB memory B cells. Notably, four individuals displayed plasma cells with identical heavy chains but different light chains, which may indicate receptor revision or clonal convergence. ACPA-producing BM plasma cells were identified in two ACPA+ patients. Three of 44 recombinantly expressed monoclonal antibodies from ACPA+ RA BM plasma cells were CCP2+, specifically binding to citrullinated peptides. Out of these, two clones reacted with citrullinated histone-4 and activated neutrophils. In conclusion, single-cell investigation of B-cell repertoires in RA bone marrow provided new understanding of human plasma cells clonal relationships and demonstrated pathogenically relevant disease-associated autoantibody expression in long-lived plasma cells.

Autoantibodies targeting malondialdehyde-modifications in rheumatoid arthritis regulate osteoclasts via inducing glycolysis and lipid biosynthesis.

Proteins subjected to post-translational modifications, such as citrullination, carbamylation, acetylation or malondialdehyde (MDA)-modification are targeted by autoantibodies in seropositive rheumatoid arthritis (RA). Epidemiological and experimental studies have both suggested the pathogenicity of such humoral autoimmunity, however, molecular mechanisms triggered by anti-modified protein antibodies have remained to be identified. Here we describe in detail the pathways induced by anti-MDA modified protein antibodies that were obtained from synovial B cells of RA patients and that possessed robust osteoclast stimulatory potential and induced bone erosion in vivo. Anti-MDA antibodies boosted glycolysis in developing osteoclasts via an FcγRI, HIF-1α and MYC-dependent mechanism and subsequently increased oxidative phosphorylation. Osteoclast development required robust phosphoglyceride and triacylglyceride biosynthesis, which was also enhanced by anti-MDA by modulating citrate production and expression of the glycerol-3-phosphate dehydrogenase 1 (GPD1) and glycerol-3-phosphate acyltransferase 2 (GPAT2) genes. In summary, we described novel metabolic pathways instrumental for osteoclast differentiation, which were targeted by anti-MDA antibodies, accelerating bone erosion, a central component of RA pathogenesis.

Cyclic Citrullinated Peptide Aptamer Treatment Attenuates Collagen-Induced Arthritis.

We describe the study of a novel aptamer-based candidate for treatment of seropositive rheumatoid arthritis. The candidate is a nanoparticle-formulated cyclic citrullinated peptide aptamer, which targets autoantibodies and/or the immune reactions leading to antibody production. Due to its specificity, the peptide aptamer nanoparticles might not interfere with normal immune functions as seen with other disease-modifying antirheumatic drugs. Over a 3-week course of treatment, joint swelling and arthritis score in collagen-induced rats were significantly decreased compared with animals treated with phosphate-buffered saline, unloaded nanoparticles, or nanoparticles with a noncitrullinated control peptide. The reduction in joint swelling was associated with decreased anticitrullinated peptide autoantibody levels in the blood. Treatment with aptamer nanoparticles also increased interleukin-10 levels. The effect seen with the proposed treatment candidate could be mediated by upregulation of anti-inflammatory mediators and decreased levels of anticitrullinated peptide antibodies.

Citrullination Controls Dendritic Cell Transdifferentiation into Osteoclasts.

An increased repertoire of potential osteoclast (OC) precursors could accelerate the development of bone-erosive OCs and the consequent bone damage in rheumatoid arthritis (RA). Immature dendritic cells (DCs) can develop into OCs, however, the mechanisms underlying this differentiation switch are poorly understood. We investigated whether protein citrullination and RA-specific anti-citrullinated protein Abs (ACPAs) could regulate human blood-derived DC-OC transdifferentiation. We show that plasticity toward the OC lineage correlated with peptidyl arginine deiminase (PAD) activity and protein citrullination in DCs. Citrullinated actin and vimentin were present in DCs and DC-derived OCs, and both proteins were deposited on the cell surface, colocalizing with ACPAs binding to the cells. ACPAs enhanced OC differentiation from monocyte-derived or circulating CD1c+ DCs by increasing the release of IL-8. Blocking IL-8 binding or the PAD enzymes completely abolished the stimulatory effect of ACPAs, whereas PAD inhibition reduced steady-state OC development, as well, suggesting an essential role for protein citrullination in DC-OC transdifferentiation. Protein citrullination and ACPA binding to immature DCs might thus promote differentiation plasticity toward the OC lineage, which can facilitate bone erosion in ACPA-positive RA.

Anticitrullinated protein antibodies facilitate migration of synovial tissue-derived fibroblasts.

OBJECTIVES: Rheumatoid arthritis (RA)-specific anti-citrullinated protein/peptide antibodies (ACPAs) might contribute to bone loss and arthralgia before the onset of joint inflammation. We aimed to dissect additional mechanisms by which ACPAs might contribute to development of joint pathology. METHODS: Fibroblast-like synoviocytes (FLS) were isolated from the synovial membrane of patients with RA. The FLS cultures were stimulated with polyclonal ACPAs (anti-CCP-2 antibodies) purified from the peripheral blood of patients with RA or with monoclonal ACPAs derived from single synovial fluid B cells. We analysed how ACPAs modulate FLS by measuring cell adhesion and mobility as well as cytokine production. Expression of protein arginine deiminase (PAD) enzymes and protein citrullination were analysed by immunofluorescence, and signal transduction was studied using immunoblotting. RESULTS: Challenge of FLS by starvation-induced stress or by exposure to the chemokine interleukin-8 was essential to sensitise the cells to ACPAs. These challenges led to an increased PAD expression and protein citrullination and an ACPA-mediated induction of FLS migration through a mechanism involving phosphoinositide 3-kinase activation. Inhibition of the PAD enzymes or competition with soluble citrullinated proteins or peptides completely abolished the ACPA-induced FLS migration. Different monoclonal ACPAs triggered distinct cellular effects in either fibroblasts or osteoclasts, suggesting unique roles for individual ACPA clones in disease pathogenesis. CONCLUSION: We propose that transient synovial insults in the presence of a certain pre-existing ACPA repertoire might result in an ACPA-mediated increase of FLS migration.

Granzyme A potentiates chemokine production in IL-17-stimulated keratinocytes.

Plaque psoriasis presents with focal skin inflammation, partially maintained by IL-17-mediated interactions between infiltrating epidermal T cells and activated keratinocytes. Here we show that the majority of lesional epidermal CD8 T cells express granzyme A, alone or in combination with IL-17. To assess proinflammatory properties of granzyme A in psoriasis, primary human keratinocytes were stimulated with granzyme A in the presence or absence of IL-17. Out of 33 analysed keratinocyte-derived inflammatory mediators, granzyme A potentiated IL-17-induced secretion of CXCL 1, CXCL 12 and CCL 4. Intriguingly, all three chemokines are implicated in psoriasis pathogenesis and are involved in recruitment of T cells, neutrophils and pDCs into inflamed tissues. Our results indicate that granzyme A produced by lesional CD8 T cells specifically increase the chemokine production from inflamed keratinocytes, thereby amplifying a chemotactic inflammatory loop that sustains psoriasis lesions.

Dendritic cell reprogramming by endogenously produced lactic acid.

The demand for controlling T cell responses via dendritic cell (DC) vaccines initiated a quest for reliable and feasible DC modulatory strategies that would facilitate cytotoxicity against tumors or tolerance in autoimmunity. We studied endogenous mechanisms in developing monocyte-derived DCs (MoDCs) that can induce inflammatory or suppressor programs during differentiation, and we identified a powerful autocrine pathway that, in a cell concentration-dependent manner, strongly interferes with inflammatory DC differentiation. MoDCs developing at low cell culture density have superior ability to produce inflammatory cytokines, to induce Th1 polarization, and to migrate toward the lymphoid tissue chemokine CCL19. On the contrary, MoDCs originated from dense cultures produce IL-10 but no inflammatory cytokines upon activation. DCs from high-density cultures maintained more differentiation plasticity and can develop to osteoclasts. The cell concentration-dependent pathway was independent of peroxisome proliferator-activated receptor γ (PPARγ), a known endogenous regulator of MoDC differentiation. Instead, it acted through lactic acid, which accumulated in dense cultures and induced an early and long-lasting reprogramming of MoDC differentiation. Our results suggest that the lactic acid-mediated inhibitory pathway could be efficiently manipulated in developing MoDCs to influence the immunogenicity of DC vaccines.

GABAergic signaling is linked to a hypermigratory phenotype in dendritic cells infected by Toxoplasma gondii.

During acute infection in human and animal hosts, the obligate intracellular protozoan Toxoplasma gondii infects a variety of cell types, including leukocytes. Poised to respond to invading pathogens, dendritic cells (DC) may also be exploited by T. gondii for spread in the infected host. Here, we report that human and mouse myeloid DC possess functional γ-aminobutyric acid (GABA) receptors and the machinery for GABA biosynthesis and secretion. Shortly after T. gondii infection (genotypes I, II and III), DC responded with enhanced GABA secretion in vitro. We demonstrate that GABA activates GABA(A) receptor-mediated currents in T. gondii-infected DC, which exhibit a hypermigratory phenotype. Inhibition of GABA synthesis, transportation or GABA(A) receptor blockade in T. gondii-infected DC resulted in impaired transmigration capacity, motility and chemotactic response to CCL19 in vitro. Moreover, exogenous GABA or supernatant from infected DC restored the migration of infected DC in vitro. In a mouse model of toxoplasmosis, adoptive transfer of infected DC pre-treated with GABAergic inhibitors reduced parasite dissemination and parasite loads in target organs, e.g. the central nervous system. Altogether, we provide evidence that GABAergic signaling modulates the migratory properties of DC and that T. gondii likely makes use of this pathway for dissemination. The findings unveil that GABA, the principal inhibitory neurotransmitter in the brain, has activation functions in the immune system that may be hijacked by intracellular pathogens.

Rapid cytoskeleton remodelling in dendritic cells following invasion by Toxoplasma gondii coincides with the onset of a hypermigratory phenotype.

Host cell manipulation is an important feature of the obligate intracellular parasite Toxoplasma gondii. Recent reports have shown that the tachyzoite stages subvert dendritic cells (DC) as a conduit for dissemination (Trojan horse) during acute infection. To examine the cellular basis of these processes, we performed a detailed analysis of the early events following tachyzoite invasion of human monocyte-derived DC. We demonstrate that within minutes after tachyzoite penetration, profound morphological changes take place in DC that coincide with a migratory activation. Active parasite invasion of DC led to cytoskeletal actin redistribution with loss of adhesive podosome structures and redistribution of integrins (CD18 and CD11c), that concurred with the onset of DC hypermotility in vitro. Inhibition of parasite rhoptry secretion and invasion, but not inhibition of parasite or host cell protein synthesis, abrogated the onset of morphological changes and hypermotility in DC dose-dependently. Also, infected DC, but not by-stander DC, exhibited upregulation of C-C chemokine receptor 7 (CCR7). Yet, the onset of parasite-induced DC hypermotility preceded chemotactic migratory responsesin vitro. Collectively, present data reveal that invasion of DC by T. gondii initiates a series of regulated events, including rapid cytoskeleton rearrangements, hypermotility and chemotaxis, that promote the migratory activation of DC.

Constraints for monocyte-derived dendritic cell functions under inflammatory conditions.

The activation of TLRs expressed by macrophages or DCs, in the long run, leads to persistently impaired functionality. TLR signals activate a wide range of negative feedback mechanisms; it is not known, however, which of these can lead to long-lasting tolerance for further stimulatory signals. In addition, it is not yet understood how the functionality of monocyte-derived DCs (MoDCs) is influenced in inflamed tissues by the continuous presence of stimulatory signals during their differentiation. Here we studied the role of a wide range of DC-inhibitory mechanisms in a simple and robust model of MoDC inactivation induced by early TLR signals during differentiation. We show that the activation-induced suppressor of cytokine signaling 1 (SOCS1), IL-10, STAT3, miR146a and CD150 (SLAM) molecules possessed short-term inhibitory effects on cytokine production but did not induce persistent DC inactivation. On the contrary, the LPS-induced IRAK-1 downregulation could alone lead to persistent MoDC inactivation. Studying cellular functions in line with the activation-induced negative feedback mechanisms, we show that early activation of developing MoDCs allowed only a transient cytokine production that was followed by the downregulation of effector functions and the preservation of a tissue-resident non-migratory phenotype.

Combination of Two Monoclonal Anti-Citrullinated Protein Antibodies Induced Tenosynovitis, Pain, and Bone Loss in Mice in a Peptidyl Arginine Deiminase-4-Dependent Manner.

OBJECTIVE: The appearance of anti-citrullinated protein antibodies (ACPAs) in the circulation represents a major risk factor for developing rheumatoid arthritis (RA). Patient-derived ACPAs have been shown to induce pain and bone erosion in mice, suggesting an active role in the pathogenicity of RA. We undertook this study to investigate whether ACPAs can induce tenosynovitis, an early sign of RA, in addition to pain and bone loss and whether these symptoms are dependent on peptidyl arginine deiminase 4 (PAD4). METHODS: Monoclonal ACPAs generated from plasma cells of RA patients were transferred to wild-type and PAD4-deficient mice. Pain-like behavior and macroscopic inflammation were monitored for a period of 4 weeks, followed by the analyses of tenosynovitis in the ankle joints using magnetic resonance imaging (MRI) and bone microarchitecture in the tibia using an X-ray microscope. Microscopic changes in the tendon sheath were analyzed in decalcified ankle joint sections. RESULTS: The combination of 2 monoclonal ACPAs (1325:04C03 and 1325:01B09) induced long-lasting pain-like behavior and trabecular bone loss in mice. Although no synovitis was observed macroscopically, we detected tenosynovitis in the ACPA-injected mice by MRI. Microscopic analyses of the joints revealed a cellular hyperplasia and a consequent enlargement of the tendon sheath in the ACPA-treated group. In PAD4-/- mice, the effects of ACPAs on pain-like behavior, tenosynovitis, and bone loss were significantly reduced. CONCLUSION: Monoclonal ACPAs can induce tenosynovitis in addition to pain and bone loss via mechanisms dependent on PAD4-mediated citrullination.

Rheumatoid Arthritis-Specific Autoimmunity in the Lung Before and at the Onset of Disease.

OBJECTIVE: The lung is implicated as a site for breach of tolerance prior to onset of seropositive rheumatoid arthritis (RA). To substantiate this, we investigated lung-resident B cells in bronchoalveolar lavage (BAL) samples from untreated early RA patients and anti-citrullinated protein antibody (ACPA)-positive individuals at risk for developing RA. METHODS: Single B cells (n = 7,680) were phenotyped and isolated from BAL samples from individuals at risk of RA (n = 3) and at RA diagnosis (n = 9). The immunoglobulin variable region transcripts were sequenced and selected for expression as monoclonal antibodies (n = 141). Monoclonal ACPAs were tested for reactivity patterns and binding to neutrophils. RESULTS: Using our single-cell approach, we found significantly increased proportions of B lymphocytes in ACPA+ compared to ACPA- individuals. Memory and double-negative B cells were prominent in all subgroups. Upon antibody re-expression, 7 highly mutated citrulline-autoreactive clones originating from different memory B cell subsets were identified, both in individuals at risk of RA and early RA patients. Lung IgG variable gene transcripts from ACPA+ individuals carried frequent mutation-induced N-linked Fab glycosylation sites (P < 0.001), often in the framework 3 of the variable region. Two of the lung ACPAs bound to activated neutrophils, 1 from an individual at risk of RA and 1 from an early RA patient. CONCLUSION: T cell-driven B cell differentiation resulting in local class switching and somatic hypermutation are evident in lungs before as well as in early stages of ACPA+ RA. Our findings add to the notion of lung mucosa being a site for initiation of citrulline autoimmunity preceding seropositive RA.

Anti-Citrullinated Protein Antibody Reactivity towards Neutrophil-Derived Antigens: Clonal Diversity and Inter-Individual Variation.

BACKGROUND: Why the adaptive immune system turns against citrullinated antigens in rheumatoid arthritis (RA) and whether anti-citrullinated protein antibodies (ACPAs) contribute to pathogenesis are questions that have triggered intense research, but still are not fully answered. Neutrophils may be crucial in this context, both as sources of citrullinated antigens and also as targets of ACPAs. To better understand how ACPAs and neutrophils contribute to RA, we studied the reactivity of a broad spectrum of RA patient-derived ACPA clones to activated or resting neutrophils, and we also compared neutrophil binding using polyclonal ACPAs from different patients. METHODS: Neutrophils were activated by Ca2+ ionophore, PMA, nigericin, zymosan or IL-8, and ACPA binding was studied using flow cytometry and confocal microscopy. The roles of PAD2 and PAD4 were studied using PAD-deficient mice or the PAD4 inhibitor BMS-P5. RESULTS: ACPAs broadly targeted NET-like structures, but did not bind to intact cells or influence NETosis. We observed high clonal diversity in ACPA binding to neutrophil-derived antigens. PAD2 was dispensable, but most ACPA clones required PAD4 for neutrophil binding. Using ACPA preparations from different patients, we observed high patient-to-patient variability in targeting neutrophil-derived antigens and similarly in another cellular effect of ACPAs, the stimulation of osteoclast differentiation. CONCLUSIONS: Neutrophils can be important sources of citrullinated antigens under conditions that lead to PAD4 activation, NETosis and the extrusion of intracellular material. A substantial clonal diversity in targeting neutrophils and a high variability among individuals in neutrophil binding and osteoclast stimulation suggest that ACPAs may influence RA-related symptoms with high patient-to-patient variability.

IL-7 modulates B cells survival and activation by inducing BAFF and CD70 expression in T cells.

Interleukin-7 (IL-7) promotes the maintenance and activation of peripheral T cells, whereas it does not act directly on mature B cells due to the lack of IL-7Rα expression on these. We report here that, in spite of the insensitivity of B cells to IL-7, high concentration of IL-7 can lead to increased B cell survival and antibody production in the presence of T cells, without the use of any further B cell stimulatory signal. IL-7 promoted B cell activation through inducing CD70 expression on resting T cells, particularly on CD4+ memory cells. The interaction of CD70 molecules with the B cell costimulatory receptor CD27 led to B cell proliferation, the accumulation of CD38 + CD20- plasmablasts and antibody production. In addition, IL-7 treatment induced BAFF secretion from resting peripheral T cells thereby promoting B cell survival. IL-7 levels can increase in lymphopenic conditions, in autoimmune diseases or in patients receiving T cell regenerative IL-7 therapy. Based on our findings high IL-7 levels can lead to increased B cell activation by inducing the B cell regulatory proteins CD70 and BAFF in resting T cells. Such activity might be beneficial in short term immune-stimulatory IL-7 therapies; permanently increased IL-7 levels, on the other hand, can contribute to impaired B cell tolerance.

Survival and proliferation of CD28- T cells during HIV-1 infection relate to the amplitude of viral replication.

BACKGROUND: CD28(-) T lymphocytes progressively increase during aging, autoimmunity, and HIV-1 infection. Expansion of these cells stands in contrast with their senescent phenotype described by several studies. Understanding the functional properties and phenotype of CD28(-) T cell during HIV-1 infection is important, because this subset incorporates T cells specific for HIV-1 and other chronic pathogens. METHODS: Blood samples were obtained from 23 healthy and 43 HIV-1-infected individuals: 26 receiving antiretroviral therapy and 17 naive to treatment. The phenotype of CD28(-) and CD28(+) T cells was determined by flow cytometry. T cells were activated through T-cell receptor before apoptosis and proliferation measurements. Interleukin (IL)-2, tumor-necrosis factor, interferon-γ, and perforin production were analyzed using enzyme-linked immunosorbent assay. RESULTS: CD28(-) T cells from patients receiving antiretroviral therapy exhibited a low sensitivity to apoptosis and enhanced proliferation after TCR stimulation, compared with T cells of uninfected individuals. On the contrary, CD28(-) T cells from viremic patients showed a decreased Bcl-2 expression, a high sensitivity to apoptosis, and poor proliferative ability, compared with treated patients and control subjects. T cells from untreated patients produced less IL-2, possibly underlying their decreased proliferative abilities. CONCLUSIONS: The level of HIV-1 replication and associated immunoactivation represent a critical factor in regulating survival and activation of CD28(-) T cells.

Current view on the pathogenic role of anti-citrullinated protein antibodies in rheumatoid arthritis.

Epidemiological findings suggest a potential role for anti-citrullinated protein antibodies (ACPAs) in rheumatoid arthritis (RA) pathogenesis. ACPA-positive RA is associated with unique genetical and environmental risk factors, in contrast to seronegative RA. ACPA-positive healthy individuals are at risk of developing RA and can develop joint pain and bone loss already before disease onset. ACPA injection triggered bone loss and pain-like behaviour in mice and, in the presence of additional arthritis inducers, exacerbated joint inflammation. In cell culture experiments, ACPAs could bind to and modulate a variety of cellular targets, such as macrophages, osteoclasts, synovial fibroblasts, neutrophil granulocytes, mast cells, dendritic cells and platelets, further underlying a potential role for these autoantibodies in triggering pathogenic pathways and providing clues for their mechanisms of action. Patient-derived ACPA clones have been characterised by unique cellular effects and multiple ways to act on the target cells. ACPAs might directly induce stimulatory signals by ligating key citrullinated cell surface molecules or, alternatively, act as immune complexes on Fc receptors and potentially other molecules that recognise carbohydrate moieties. On the contrary to experimentally manufactured ACPA clones, patient-derived ACPAs are highly promiscuous and cross-reactive, suggesting a simultaneous binding to a range of functionally relevant and irrelevant targets. Moreover, several ACPA clones recognise carbamylated or acetylated targets as well. These features complicate the identification and description of ACPA-induced pathogenic mechanisms. In the current review, we summarise recent data on the functional properties of patient-derived ACPAs and present mechanistic models on how these antibodies might contribute to RA pathogenesis.

An Image-based Dynamic High-throughput Analysis of Adherent Cell Migration.

In this protocol, we describe a method to monitor cell migration by live-cell imaging of adherent cells. Scratching assay is a common method to investigate cell migration or wound healing capacity. However, achieving homogenous scratching, finding the optimal time window for end-point analysis and performing an objective image analysis imply, even for practiced and adept experimenters, a high chance for variability and limited reproducibility. Therefore, our protocol implemented the assessment for cell mobility by using homogenous wound making, sequential imaging and automated image analysis. Cells were cultured in 96-well plates, and after attachment, homogeneous linear scratches were made using the IncuCyte ® WoundMaker. The treatments were added directly to wells and images were captured every 2 hours automatically. Thereafter, the images were processed by defining a scratching mask and a cell confluence mask using a software algorithm. Data analysis was performed using the IncuCyte ® Cell Migration Analysis Software. Thus, our protocol allows a time-lapse analysis of treatment effects on cell migration in a highly reliable, reproducible and re-analyzable manner.