Functional characteristics of synovial fluid and blood mononuclear cells in rheumatoid arthritis and traumatic synovitis

Responses to Cytokine Inhibitors Associated with Cellular Composition in Models of Immune-Mediated Inflammatory Arthritis

Objective

Immune‐mediated inflammatory arthritis (IMIA) is a heterogeneous group of diseases including rheumatoid arthritis (RA), psoriatic arthritis (PsA), and spondyloarthritis (SpA). Disease‐modifying antirheumatic drugs (DMARDs) target very different cellular components of the disease processes. Characterization of the pathobiological subtypes of IMIA could provide more specific treatment approaches for each disease. For example, RA has been proposed to consist of at least three synovial pathotypes (lymphoid, myeloid, and fibroid), and only a subgroup of RA patients have erosive disease. The objective of this study was to evaluate the effects of various DMARDs on different synovial cell subsets using human ex vivo models of IMIA.

Methods

Synovial fluid and blood samples were obtained from a study population consisting of patients with RA, PsA, or peripheral SpA with at least one swollen joint (n = 18). The DMARDs used in this study were methotrexate, adalimumab, etanercept, tocilizumab, anakinra, ustekinumab, secukinumab, tofacitinib, and baricitinib. Paired synovial fluid mononuclear cells (SFMCs), peripheral blood mononuclear cells (PBMCs), and fibroblast‐like synovial cells (FLSs) were used in three different previously optimized ex vivo models.

Results

In SFMCs cultured for 48 hours, all DMARDs except anakinra decreased the production of monocyte chemoattractant protein (MCP)‐1. In SFMCs cultured for 21 days, only the two tumor necrosis factor alpha (TNFα) inhibitors adalimumab and etanercept decreased the secretion of tartrate‐resistant acid phosphatase (P < 0.01, P < 0.001). In the FLS and PBMC 48‐hour co‐cultures, only tocilizumab (P < 0.001) and the two Janus kinase inhibitors tofacitinib and baricitinib (both P < 0.05) decreased the production of MCP‐1 by around 50%.

Conclusion

TNFα inhibition was effective in preventing inflammatory osteoclastogenesis, whereas tocilizumab, tofacitinib, and baricitinib had superior efficacy in cultures dominated by FLSs. Taken together, this study reveals that responses to cytokine inhibitors associate with cellular composition in models of IMIA. In particular, this study provides new evidence on the differential effect of DMARDs on leukocytes compared with stromal cells.

Heat shock (stress) proteins and autoimmunity in rheumatic diseases

The rheumatic diseases (RDs) are characterized by acute and chronic inflammation, and autoimmunity plays a major role in their pathogenesis. RDs are for the most part of unknown etiology, but recent evidence indicates that heat shock or stress proteins (HSPs) may have an important role in the etiology/pathogenesis of RDs. HSPs are produced by prokaryotic and eukaryotic cells and are grouped according to molecular weight. Phylogenetically, HSPs are very old and are remarkably conserved molecules in evolution from bacteria to humans. HSPs are induced by a variety of cellular stresses in addition to heat; cognates are expressed constitutively and are essential in a number of normal functions. Some HSPs serve as molecular chaperones, the latter defined as proteins that mediate folding of other polypeptides and either promote their assembly into oligomeric structures or disassemble the final product. Conservation of structure and function of many HSPs may provide a link between immunity to infection and the autoimmune features of RDs. Evidence is reviewed from clinical and laboratory observations that diverse microbial agents, including viruses, bacteria, and parasites, may have putative roles in the development and pathogenesis of some RDs. HSPs also are discussed in relation to the major histocompatibility complex, HLA antigens, and disease associations and how they may alter the balance between tolerance and autoimmunity. Studies are reviewed that are supportive or nonsupportive of the concept of microbial infection associated with autoimmunity; individuals first react to microbial immunizations or infections with enhanced cellular/humoral responses to the agent's HSPs. With the enhanced immune response, cross-reactivity may occur with an HSP of the stressed host because of structural similarities to the microbial HSP. If all of these events occur, the host's homologous HSP or stressed cells now become true autoantigen(s). This sequence has implications for the etiology of immune-mediated RDs, the concept of epitope sharing, and the accompanying autoimmunity. A recurring theme emphasized in some reports to understand better the role of HSPs in autoimmunity is the need to select patients with early-onset disease. A minor subpopulation of T lymphocytes express a CD3-associated T-cell receptor (TCR) heterodimer composed of gamma and delta polypeptide chains. The gamma delta + T cells have several unique features. When analyzed by the polymerase chain reaction, lymphocytes with TCR-gamma delta appear to reflect the polyclonal expansion of preexisting gamma delta clones. They are found in peripheral lymphoid tissue in very low percentage (< 5%) but may represent the majority of T cells within epithelial tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigenic specificity of rheumatoid synovial fluid lymphocytes

The majority of rheumatoid arthritis (RA) synovial fluid lymphocytes (SFL) demonstrate markers that are suggestive of prior activation. While the mechanism(s) responsible is unknown, prior studies have suggested that certain Mycobacterium tuberculosis (MT) antigens may preferentially activate SFL in vitro. We therefore examined the ability of RA SFL to respond to purified protein derivative and an acetone-precipitable MT antigenic complex (AP-MT) and compared this with the responses by peripheral blood lymphocytes (PBL). The responses were contrasted with those elicited with tetanus toxoid (TT) and mitogenic anti-CD3. In patients with RA, the SF proliferative responses to both TT and anti-CD3 were reduced compared with responses by PB. In contrast, the SF response to purified protein derivative was maintained, and that to AP-MT was significantly increased, compared with PB. SF responses to AP-MT antigens were significantly greater than those to TT. The AP-MT activation of T lymphocytes from RA SF was characterized by an earlier peak proliferative response than that noted with matched PB. AP-MT responsiveness was not restricted to HLA-DR4 positive patients. These observations suggest that an epitope(s) contained within the MT complex of antigens, and enriched in the AP-MT complex, may be important in maintaining the chronic inflammation in at least some patients with RA.

Interleukin-1-like activities in synovial fluids of patients with rheumatoid arthritis and traumatic synovitis

Interleukin-1 (Il-1)-like activity in biological fluids was measured by their ability to rectify the Il-1-dependent lymphokine production of highly purified T lymphocytes to a recall antigen. Il-1-like activity was found in 9 of 11 synovial fluid (SF) specimens from patients with rheumatoid arthritis (RA) but only in 2 of 11 paired RA sera. In traumatic synovitis, low Il-1-like activity was recorded in 5 of 9 SF specimens, and a similar low activity was found in sera of 4 of these patients. The Il-1-like activity was partly absorbed by an anti-Il-1 antibody. The presence of Il-1 in the SF of patients with RA suggests in vivo activation of monocytes/macrophages.

Spontaneous and induced immunoglobulin secretion by synovial fluid B lymphocytes in rheumatoid arthritis

The functional properties of B lymphocytes in synovial fluid (SF) from patients with rheumatoid arthritis (RA) were analysed by means of a reverse haemolytic plaque forming cell (PFC) assay. SF mononuclear cells spontaneously secreted IgG, but little IgM or IgA. The SF cells failed to respond to the polyclonal B cell activators pokeweed mitogen (PWM) and Epstein-Barr virus. However, SF B cells cocultured with autologous T lymphocytes from the blood and stimulated with PWM secreted IgG but little IgM or IgA. The PFC responses of blood B cells cocultured with autologous SF T cells in the presence of PWM were low; irradiation of the T cells increased the blood B lymphocyte responses, but the differences were not statistically significant. It is concluded that suppressor SF T cells may be partly responsible for the poor response of SF B cells to PWM.

Synovial fluid and blood monocytes/macrophages in rheumatoid arthritis. Influence on polyclonal activation of autologous B lymphocytes

The regulatory role of synovial fluid monocytes/macrophages from patients with rheumatoid arthritis in terms of B lymphocyte activation was evaluated by a reverse haemolytic plaque-forming cell (PFC) assay. Macrophage-depleted blood mononuclear cells (BMC) failed to respond to pokeweed mitogen (PWM). With autologous synovial fluid macrophages added, the PFC responses of macrophage-depleted BMC increased, and optimal concentration for full restoration of the PFC responses ranged from 8 to 35%. Synovial fluid mononuclear cells (SMC) as well as macrophage-depleted SMC were not able to respond to PWM. Addition of irradiated autologous blood macrophages to SMC did not increase the SMC PFC responses. It is concluded that the regulatory properties of synovial fluid macrophages do not explain the low PFC response of SMC to PWM.

IgG rheumatoid factor-secreting lymphocytes in rheumatoid arthritis: evaluation of a haemolytic plaque-forming cell technique

A haemolytic plaque-forming cell (PFC) assay detecting human B lymphocytes secreting IgG rheumatoid factor (RF) was established using sheep erythrocytes (SRBC) sensitized with rabbit IgG, developing rabbit anti-human IgG, and complement. IgG-RF PFC were only demonstrated with IgG-depleted guinea-pig serum as the source of complement. Cells spontaneously secreting IgG-RF were found among synovial fluid mononuclear cells (mean, 134/10(6)) and synovial tissue mononuclear cells (mean, 1775/10(6)) from patients with rheumatoid arthritis, whereas few were recorded among blood lymphocytes (mean, 3/10(6)). The experiments revealed that the RF-IgG PFC were protein-synthesizing B lymphocytes. The antibody specificity of the secreted IgF-RF was verified by the inhibitory effect of exogenous human and rabbit IgG on PFC formation.

Synovial fluid and blood monocyte influence on lymphocyte proliferation in rheumatoid arthritis and traumatic synovitis

The influence of synovial fluid and blood monocytes on autologous lymphocyte proliferation in vitro was investigated in patients with rheumatoid arthritis (RA) and traumatic synovitis (TS). In cultures stimulated with PHA, PWM and ConA, thymidine incorporation by RA blood mononuclear cells (BMC) increased considerably in most cases after addition of 10% or 30% synovial fluid monocytes and a similar effect was seen after stimulation with Candida extract or PPD. A comparable helper activity was observed after addition of synovial fluid monocytes to monocyte-depleted blood cells in RA. The augmenting effect of synovial fluid monocytes was likewise demonstrated in TS patients. Synovial fluid mononuclear cells (SMC) from RA and TS patients displayed low proliferative responses to PHA and ConA in comparison with BMC, while the responses to microbial antigens were similar or greater. The proliferative activity of SMC or of monocyte-depleted synovial fluid cells after polyclonal and antigenic stimulation was not affected by addition of blood monocytes. This was observed in both RA and TS patients. It is concluded that the regulatory properties of synovial fluid monocytes in RA and TS do not explain the low proliferative responses of SMC to polyclonal activators.

Immunosuppressive actions of gold salts

In rheumatoid arthritis both lymphocyte-mediated and antibody-mediated immune reactions are important for the inflammatory lesions. In vivo activated B lymphocytes/plasma cells, T lymphocytes and monocytes/macrophages (Mo) are intimately involved in the disease process. Several clinical observations suggest an immunosuppressive action of gold salts. In humans, gold salts interfere with a number of Mo functions in vitro, including cellular interactions between Mo and T lymphocytes. Some workers have shown that the activation of human T lymphocytes is inhibited by gold salts, most probably secondary to an inhibition of Mo-T cell cooperation. Recent experiments indicate that gold salts also affect the in vitro differentiation of human B lymphocytes in response to polyclonal activators. Both the gold atom and the SH group seem to be important for the immunosuppressive actions of gold salts.