Platelet releasing activity in sera of patients with rheumatoid vasculitis.

Platelet releasing activity was found in sera fractionated by 30% ammonium sulphate in seven of 11 patients with systemic rheumatoid vasculitis, two of 16 patients with cutaneous rheumatoid vasculitis, and three of 18 patients with clinically uncomplicated rheumatoid arthritis. Serial studies in three patients suggest a key role of platelet activation by serum factors in the pathogenesis of systemic rheumatoid vasculitis. IgG rheumatoid factor or IgG containing immune complexes, or both, may be responsible for this platelet releasing activity.