Mast cells were isolated by enzymatic digestion of synovium obtained from 48 patients with rheumatoid arthritis (RA) and 42 patients with osteoarthritis (OA). A significantly lower percentage of stainable synovial mast cells was obtained by tissue digestion from patients with clinically active RA compared with those with less active disease. The 54 patients treated with nonsteroidal antiinflammatory drugs had a significantly lower percentage of stainable synovial mast cells in cell suspension than did the other 36 patients. When anti‐IgE antibody was used as a secretagogue in vitro, significantly greater histamine release was observed from synovial mast cells of RA patients compared with OA patients. Greater histamine release in response to anti‐IgE was observed in the RA patients with more clinically active disease and those who were treated with prednisone, compared with RA patients without these features. Synovial mast cells of RA patients treated with a disease‐modifying antirheumatic drug had a significantly lower mean histamine content than did cells from patients not receiving such treatment. Our data suggest that there are differences between synovial mast cells from tissues of patients with RA and OA and suggest that synovial mast cells may be activated in clinically active RA. In addition, the data indicate an effect of systemic anti‐rheumatic therapy on mast cells isolated from synovium of patients with arthritis.

Beta-adrenergic agonists can prevent mediator release from guinea pig pulmonary mast cells. By pharmacologic characterization, this response is mediated through a beta-2 receptor. Structural characterization of this receptor on the lung mast cell, however, has been limited by methods for isolation of this pulmonary cell. In this study, the guinea pig lung mast cell was isolated to greater than 90% purity, and its beta-adrenergic receptor identified by photoaffinity labeling with [125I]iodoazidobenzylpindolol (125IABP) and separation of membrane proteins by SDS-PAGE. We found the guinea pig pulmonary mast cell beta-adrenergic receptor to electrophorese as a heterogeneous protein between 68 and 116 kD. Photoaffinity labeling with 125IABP was protectable by alprenolol and isoproterenol but not by phentolamine and norepinephrine. Using subtype-selective compounds, the pulmonary mast cell receptor was established to be of a beta-2 subtype. This is the first report of the structural identification of a lung mast cell beta-adrenergic receptor and the first report of a beta-adrenergic receptor of approximately 100 kD in mass. This mast cell receptor is considerably larger than the 65 kD beta-adrenergic receptors that have been identified in whole lung and other tissues. Data we have obtained using Northern blot analysis of mast cell RNA suggest a protein message of 45 kD for this beta-adrenergic receptor and a high degree of glycosylation most likely accounts for the large molecular size observed.

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