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Introduction: The purpose of this study was to examine the role of RA Synovial Fibroblast (RASFib) IL-15 expression on B cell survival., Methods: Magnetically sorted peripheral blood memory B cells from 15 healthy subjects were cocultured with RASFib., Results: RASFib constitutively expressed membrane IL-15. Survival of isolated B cells cultured for 6 days, below 5%, was extended in coculture with RASFib to 52+/-8% (p<0.001). IL-15 neutralizing agents but not isotype controls, reduced this rate to 31+/-6% (p<0.05). Interestingly, rhIL-15 had no effect on isolated B cells but significantly increased their survival in coculture with RASFib. In parallel, B cell IL-15R chains were upregulated in cocultures. BAFF and VCAM-1, that are expressed on RASFib, were tested as potential candidates involved in upregulating B cell IL-15R. Culture of B cells in the presence of rhBAFF or rhVCAM-1 resulted in significantly increased survival, together with upregulation of all three IL-15R chains; in parallel, rhIL-15 potentiated the anti-apoptotic effect of BAFF and VCAM-1. Both BAFF and VCAM-1 neutralizing agents downmodulated the effect of RASFib on B cell survival and IL-15R expression. In parallel, rhIL-15 had a lower effect on the survival of B cells cocultured with RASFib in the presence of BAFF or VCAM-1 neutralizing agents. Peripheral blood B cells from 15 early RA patients demonstrated an upregulated IL-15R and increased survival in cocultures., Conclusion: IL-15 expression on RASFib significantly contributes to the anti-apoptotic effect of RASFib on B cells. IL-15 action is facilitated by BAFF and VCAM-1 expressed on RASFib, through an upregulation of IL-15R chains.

We previously described that fibroblast-like cells from the synovium of rheumatoid arthritis patients (RASFib) constitutively express intracellular and surface IL-15, which induces activation of cocultured T cells. Our objective was to study the effect of RASFib IL-15 expression on the function of human CD4(+)CD25(+) regulatory T cells (Treg). RASFib, through their constitutive IL-15 expression, were able to induce the proliferation of human Tregs stimulated through their TCR, and at the same time potentiated their suppressive action on the cytokine secretion of CD4(+)CD25(-) responder T cells (Tresp). In parallel, constitutive RASFib IL-15 expression mediated an up-regulated response of Tresp. Subsequently, total CD4(+) T cells, containing natural proportions of Treg and Tresp, secreted an increased amount of pathogenic cytokines when cocultured with RASFib despite the presence of proliferating Treg with superior regulatory potency. In summary, RASFib IL-15 exerts a dual action on the equilibrium between Treg and Tresp by potentiating the suppressive effect of Treg while augmenting the proinflammatory action of Tresp; the result is a shift of the Treg/Tresp balance toward a proinflammatory state. This alteration of the Treg/Tresp equilibrium is not observed in the presence of osteoarthritis synovial fibroblasts or dermal fibroblasts, which do not constitutively express surface IL-15. Additionally, Treg with superior suppressive potency were present in the peripheral blood and the synovial fluid of RA patients, but this enhanced immunoregulatory activity was not able to overcome the increased secretion of pathogenic cytokines by RA-Tresp, indicating that rheumatoid arthritis patients demonstrate an altered Treg/Tresp equilibrium in vivo.

Objective: To examine fibroblasts grown from the synovial fluid of rheumatoid arthritis (RA) patients for TRAIL-R2 expression, and for susceptibility to apoptosis induced by an agonistic anti-TRAIL-R2 monoclonal antibody (mAb)., Methods: The expression of TRAIL-R2 (DR5) was determined by flow cytometry on fibroblasts grown from the synovial fluid of patients with RA, osteoarthritis (OA), seronegative arthritis, and unclassified monarthritis or oligoarthritis, and on fibroblasts from the synovial membrane of RA and OA patients. Susceptibility to apoptosis mediated by an agonistic anti-TRAIL-R2 mAb was determined by alamar blue bioassay, fluorescence microscopy (annexin V/propidium iodide staining), and caspase activation., Results: Fibroblasts grew from 35 of 50 RA synovial fluid samples, of which 26 were DR5(+) (mean [+/-SD] fluorescence intensity [MFI] 18.74 +/- 2.5). Fibroblasts also grew from 15 of 30 seronegative arthritis synovial fluid samples, 28 of 40 OA synovial fluid samples, and 8 of 20 unclassified monarthritis or oligoarthritis synovial fluid samples; all of these were DR5- (MFI 0.32 +/- 0.02). All 10 of the fibroblast lines from joint replacement surgery or synovectomy specimens of RA patients were DR5(+) (MFI 20.3 +/- 3.2). All fibroblast lines from the synovium of 10 OA patients were DR5-, as were fibroblasts from the skin of 5 healthy subjects. DR5(+) fibroblast cultures underwent apoptosis when treated in vitro with an agonistic anti-DR5 antibody., Conclusion: Fibroblasts grown from the synovial fluid and synovial membrane of RA patients express TRAIL-R2 that is functionally active. An agonistic anti-TRAIL-R2 antibody that does not induce hepatocyte toxicity may be an alternative strategy for treatment of RA.

To characterize the molecules responsible for synovial fibroblast-T lymphocyte (TL) cross-talk in rheumatoid arthritis (RA), synovial fibroblasts from patients with established RA (RASFibs) were cocultured with TLs from peripheral blood of early RA patients (RAPBTL). TLs from peripheral blood of healthy controls and from synovial fluid of RA served as controls. Adhesion molecules and cytokines were determined by flow cytometry, ELISA, and real-time PCR. RAPBTL (n = 20) induced an up-regulation of ICAM-1, intracellular IL-8, IL-6, IL-15, and surface IL-15 in cocultured RASFibs. In turn, RAPBTL showed an up-regulation of TNF-alpha, IFN-gamma, IL-17, CD25, and CD69 expression. Responses seen with TLs from peripheral blood of healthy controls (n = 20) were significantly lower, whereas responses with TLs from synovial fluid of RA (n = 20) were maximal. Blocking Abs to IL-15 and CD54, but not an isotype-control Ab, down-regulated the increased TL cytokine and activation marker expression. Abs to CD69, CD11a, IL-17, TNF-alpha, and IFN-gamma significantly decreased the up-regulation of RASFib cytokine and CD54 expression. Cocultures using 0.4- micro m inserts did not result in up-regulation of surface molecules or cytokines. Methotrexate significantly inhibited RASFib/TL cross-talk signals and decreased adhesion of TL to RASFibs. In summary, RASFib production of IL-15 induces the proinflammatory cytokines TNF-alpha, IFN-gamma, and IL-17 in cocultured TLs through a cell contact-dependent mechanism. In turn, these cytokines stimulate the expression of IL-15, IL-8, and IL-6 in RASFibs, thereby creating a feedback loop that favors persistent synovial inflammation. Methotrexate seems to disrupt this loop by decreasing cell adhesion.