Mast Cell Activation in Arthritis: Detection of α- and β-tryptase, Histamine and Eosinophil Cationic Protein in Synovial Fluid

Abstract

1. Although mast cell hyperplasia is a feature of rheumatoid arthritis and osteoarthritis, the extent and nature of mast cell activation in joint disease have not been clearly established. 2. We have investigated the levels of mast cell tryptase and histamine and also of eosinophil cationic protein in synovial fluid collected from 31 patients with rheumatoid arthritis, 14 with seronegative spondyloarthritis and nine with osteoarthritis. Two RIAs for tryptase were employed: one with monoclonal antibody AA5, which was found to bind equally well to both alpha and beta isoforms on Western blots of the recombinant enzyme, and the other with antibody G5, which recognizes predominantly beta-tryptase. 3. alpha-Tryptase, which is likely to be released constitutively from mast cells, appeared to be the major form in synovial fluid, as the assay with antibody AA5 detected appreciably more tryptase than that with antibody G5. beta-Tryptase, which is released on anaphylactic activation of mast cells, was detected in 14 out of 45 synovial fluid samples studied, with concentrations of up to 12 micrograms/l measured by the G5 assay. The apparent levels of beta-tryptase, but not of alpha-tryptase, were closely correlated with those of histamine in the synovial fluid. Patients with osteoarthritis appeared to have a greater proportion of beta-tryptase in the synovial fluid than those with rheumatoid arthritis, as well as higher concentrations of histamine. Eosinophil cationic protein was present at high levels in the synovial fluid, although eosinophil numbers were low, and its concentrations were not correlated with the concentrations of the mast cell products. 4. These data suggest that anaphylactic degranulation of mast cells may have occurred to a greater extent in osteoarthritis than in rheumatoid arthritis, despite the relative lack of synovial inflammation in osteoarthritis. Although the eosinophil cationic protein detected may not reflect eosinophilic inflammation in the joint, the presence in synovial fluid of tryptase of both major forms, and of histamine, appears to indicate that mast cell products are secreted constitutively, as well as by processes of anaphylactic degranulation in rheumatoid arthritis, seronegative spondyloarthritis and osteoarthritis.

A Novel Mechanism for Bradykinin Production at Inflammatory Sites

“…3B it is apparent that at 0.1 M elastase concentration, the effective tryptase concentration is as low as 1 nM. Tryptase, at this or even higher levels, has been found in several pathophysiological fluids, including allergic nasal lavages (64), synovial fluid (50), and the plasma of patients who died of anaphylaxis (65).…”

“…This event thus brings together both proteinases for concerted action on kininogens supplied in plasma exudate induced by increased vascular permeability originally caused by histamine release and perpetuated by locally generated kinins. Indeed, a vast body of literature indicates that at least in synovial fluid both elastase and tryptase coexist (47)(48)(49)(50)(51)(52)(53), and the presence of fibrinogen-and IgG-derived fragments in this fluid (49,54) indicates that the HNE-catalyzed degradation of functional proteins can occur under in vivo conditions.…”

Two distinct forms of human mast cell chymase

“…Rabbit antisera to RMCP-1 and RMCP-2 can cross-react on western blots [54] and several mAbs react with equal affinity for both and A-tryptase and β-tryptase, which exhibit 91% sequence similarity [55,56]. Both chymases reacted with antiserum raised against a synthetic peptide corresponding to residues 56Ϫ70, which suggests this region is highly conserved between the two chymases.…”

Activation of human tonsil and skin mast cells by agonists of proteinase activated receptor-2

“…Tryptase and histamine measurement Tryptase concentrations were measured with a sandwich ELISA procedure with a specific polyclonal antibody against human tryptase as the capture antibody and AA5 a monoclonal antibody specific for human tryptase (both donated by Dr Andrew FW, University of Southampton, UK) as the detecting antibody [18] . Histamine concentrations were determined using a glass fibre-based fluorometric assay [16] .…”