Increased extracellular Ca 2+ concentrations ([Ca 2+ ] 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 [Ca 2+ ] ex. Enhanced macropinocytosis of CPPs results in increased lysosomal activity, NLRP3 inflammasome activation, and IL-1β release. Monocytes in the context of rheumatoid arthritis (RA) exhibit increased CPP uptake and IL-1β release in response to CaSR signaling. CaSR expression in these monocytes and local [Ca 2+ ] 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 CaSRmediated CPP uptake might be a therapeutic approach to treating RA.

Peripheral CD4CD8 double positive (DP) T cells have been reported to play a role in several autoimmune diseases, virus infections and cancer. In rheumatoid arthritis (RA), both CD4 and CD8 single positive (SP) T cells are known to be involved in the pathogenesis, but the role of peripheral CD4CD8 DP T cells has not been investigated in detail. Anti cyclic citrullinated antibodies (ACPA) positive and ACPA negative RA patients, patients with systemic lupus erythematodes (SLE) and age matched healthy donors (HD) were enrolled in the analysis. The frequencies and phenotype of DP T cells in PBMC were investigated. In addition, DP T cells were quantified in biopsies from rheumatoid synovium. After in vitro restimulation, the cytokine production of DP T cells was investigated in cultures of PBMC. CMV specific cytokine secretion as well as proliferation was analyzed following antigen specific restimulation after an appropriate culture duration. DP T cells were found more frequently in RA patients than in healthy controls or patients with SLE. These DP T cells express αβ TCRs, are of a memory phenotype and share features of both CD4 as well as CD8 SP T cells. Importantly, DP T cells were found to also be present in the rheumatoid synovium. Further characterization of DP T cells from RA patients revealed increased production of IL-21 and IL-4, implying a possible role as T helper cells. In addition, DP T cells in RA seem to contribute to the inflammatory process, because they produce significantly more IFNγ than counterparts from HD and are increased in CMV+ RA patients. Given their capacity to produce a variety of cytokines (IL4, IL21 and IFNγ), their association with ACPA positive RA and their presence in the synovium, we suggest an important role of double positive T cells in the pathogenesis of rheumatoid arthritis.

Objective. Expansion of autoreactive CD4؉ CD28null 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-␣ (IFN␣), 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

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IntroductionRheumatoid arthritis (RA) is a chronic disease of joints that is characterized by three main manifestations, namely inflammation, abnormal cellular and humoral immunoresponse, and synovial hyperplasia. Eventually the interplay between these pathologic processes leads to complete joint destruction [1].A hallmark of RA is infiltration of leukocytes into synovial tissue, mediated by a complex network of cytokines, adhesion molecules and chemoattractants [2][3][4][5][6]. The presence of activated leukocytes contributes to persistence of destructive synovitis [6,7]. Nevertheless, leukocyte recruitment to the joint is not yet fully understood. The presence of specific functional and inflammatory T-cell subsets that CXCL = Cys-X-Cys ligand; CXCR = Cys-X-Cys receptor; G3PDH = glyceraldehyde-3-phosphate dehydrogenase; IFN = interferon; IL = interleukin; MC = mast cell; OA = osteoarthritis; PBS = phosphate buffered saline; PCR = polymerase chain reaction; RA = rheumatoid arthritis; RT = reverse transcription; TCR = T-cell receptor; Th = T-helper (cell).