The membrane proteinase 3 expression on neutrophils was downregulated after treatment with infliximab in patients with rheumatoid arthritis.

Proteinase 3 (PR3) expression on neutrophils was examined in rheumatoid arthritis (RA) patients before and after antitumor necrosis factor (TNF)-alpha therapy. Membrane PR3 expression from patients with either an infection or RA significantly increased. Membrane PR3 expression on neutrophils from RA patients treated with infliximab (anti-TNF-alpha antibody) therapy was less than in those without such treatment in a resting state, but the expression later increased after stimulation in vitro. Membrane PR3 expression increased because of the stimulation of TNFalpha, whereas it was significantly suppressed by plasma or alpha(1)-proteinase inhibitor. The condition of patients with RA improved after treatment with infliximab. Membrane PR3 expression on neutrophils in RA patients was downregulated by infliximab. As a result, PR3 might play an important role in the neutrophil-mediated inflammatory reaction in patients with either RA or an infection.