Expression of the C5a receptor (CD88) on synovial mast cells in patients with rheumatoid arthritis

Tumor necrosis factor α promotes the expression of stem cell factor in synovial fibroblasts and their capacity to induce mast cell chemotaxis

“…An increasing body of evidence suggests that synovial MC are involved in the inflammatory process of arthritis (30)(31)(32)(33)(34)(35). First, synovial MC increase in number in both RA and OA, and show signs of activation.…”

“…It also has been reported that synovial MC express functional receptors for SCF and release histamine in response to recombinant SCF (35,42). These observations have suggested that SCF plays a role in the accumulation and activation of MC in the synovium of patients with RA and OA.…”

“…Therefore, it was tempting to speculate that SCF is involved in the accumulation of MC in the synovium in RA and OA. Indeed, synovial MC express functional SCF receptor (c-kit/CD117) (35,42). In the present study, we found that cultured SFB express and release SCF, and thereby induce MC chemotaxis.…”

“…MC reportedly produce a number of proinflammatory mediator substances, including histamine, TNF␣, and proteases, and can release such compounds in response to cell activation by IgE-dependent or IgE-independent stimuli (13)(14)(15)(16)(17)(21)(22)(23). The observation that SCF induces mediator release in synovial MC in RA and OA suggests that these compounds play a role in MC-dependent reactions in patients with synovitis (35,42). In this regard, it is of interest that significant levels of histamine can be found in the synovial fluid of patients with RA (47).…”

Selective activation of mast cells in rheumatoid synovial tissue results in production of TNF-α, IL-1β and IL-1Ra

“…It is, however, unlikely that in RA, mast cells are activated through IgE-dependent pathways although rheumatoid factor belonging to IgE class of immunoglobulins has been described in a small subset of RA patients [23]. Rather, the synovial mast cells in RA are likely to be activated by complement components such as C5a and/or by immune complexes [24,8]. Unfortunately activation of mast cells by using these compounds would stimulate also other cell types in synovial tissue, macrophages and neutrophils in particular, besides the mast cells.…”