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.

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.

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).

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.

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.

Programmed death ligand 2 - A link between inflammation and bone loss in rheumatoid arthritis.

Objective: Active rheumatoid arthritis (RA) is accompanied by increased appendicular and axial bone loss, closely associated to the degree of inflammation. The programmed death-1 (PD-1) pathway is important for maintaining peripheral tolerance, and its ligand PD-L2 has recently been associated with bone morphogenetic protein activity. Here, we report that PD-L2 plays a central role in RA osteoimmunology.

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.

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.

Recognition of Amino Acid Motifs, Rather Than Specific Proteins, by Human Plasma Cell-Derived Monoclonal Antibodies to Posttranslationally Modified Proteins in Rheumatoid Arthritis.

Objective: Antibodies against posttranslationally modified proteins are a hallmark of rheumatoid arthritis (RA), but the emergence and pathogenicity of these autoantibodies are still incompletely understood. The aim of this study was to analyze the antigen specificities and mutation patterns of monoclonal antibodies (mAb) derived from RA synovial plasma cells and address the question of antigen cross-reactivity.

Methods: IgG-secreting cells were isolated from RA synovial fluid, and the variable regions of the immunoglobulins were sequenced (n = 182) and expressed in full-length mAb (n = 93) and also as germline-reverted versions.

Autoreactivity to malondialdehyde-modifications in rheumatoid arthritis is linked to disease activity and synovial pathogenesis.

Oxidation-associated malondialdehyde (MDA) modification of proteins can generate immunogenic neo-epitopes that are recognized by autoantibodies. In health, IgM antibodies to MDA-adducts are part of the natural antibody pool, while elevated levels of IgG anti-MDA antibodies are associated with inflammatory and autoimmune conditions. Yet, in human autoimmune disease IgG anti-MDA responses have not been well characterized and their potential contribution to disease pathogenesis is not known.

Autoantibodies to citrullinated proteins induce joint pain independent of inflammation via a chemokine-dependent mechanism.

Objective: An interesting and so far unexplained feature of chronic pain in autoimmune disease is the frequent disconnect between pain and inflammation. This is illustrated well in rheumatoid arthritis (RA) where pain in joints (arthralgia) may precede joint inflammation and persist even after successful anti-inflammatory treatment. In the present study, we have addressed the possibility that autoantibodies against citrullinated proteins (ACPA), present in RA, may be directly responsible for the induction of pain, independent of inflammation.

Identification of a novel chemokine-dependent molecular mechanism underlying rheumatoid arthritis-associated autoantibody-mediated bone loss.

Objectives: Rheumatoid arthritis (RA)-specific anti-citrullinated protein/peptide antibodies (ACPAs) appear before disease onset and are associated with bone destruction. We aimed to dissect the role of ACPAs in osteoclast (OC) activation and to identify key cellular mediators in this process.

Methods: Polyclonal ACPA were isolated from the synovial fluid (SF) and peripheral blood of patients with RA.

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.