Human mononuclear cells and neutral proteinases

We have been interested in contributions of certain cells and mediators to synovial inflammation rheumatoid arthritis (RA). The present studies were designed to determine (1) whether monocytes contained the neutral proteinase cathepsin G and (2) if neutral proteinase could induce or potentiate cellular IgM rheumatoid factor (RF) production. Monocyte-rich and monocyte-poor populations were isolated by Ficoll-Hypaque density sedimentation followed by glass adherence, and cellular lysates were obtained by repetitive freezing and thawing as we have reported for neutrophil-derived neutral proteinase. Cathepsin G was quantified immunochemically by an enzyme-linked irnmunoassay (ELISA) we developed utilizing commercially available anti-cathepsin G antibodies. Mononuclear and B-cel!-enriched cell cultures were prepared by standard methods and IgM RF measured by our ELISA. Cell-derived lysates from monocyte-enriched populations (84+3% monocytes, less than 1 % neutrophils) contained considerably greater amounts of measurable cathepsin G (OD₂₈₀=0.393±0.153) than lysates from equal numbers of monocyte (15±2% monocytes, less than 1% neutrophils) -depleted cells (OD₂₈₀=0.071±0.038;P<0.05). Eighteen patients with RA and three normal individuals did not have consistently increased cellular elaboration of Ig or IgM RF in vitro in response to proteinase (trypsin) stimulation; however, patients manifested 80% potentiation by trypsin of pokeweed-stimulated cellular IgM RF production in vitro (pokewee-dstimulated IgM RF 137±53 ng/mi, pokeweed/trypsin-induced IgM RF 246±100 ng/ml;P<0.02), changes being most striking for those patients seropositive by latex fixation test (84% increase,P<0.02). These data indicate that monocytes and/or macrophages localized to sites of inflammation are a source of cathepsin G and that neutral proteinases may potentiate cellular activation and auto antibody production in processes such as rheumatoid arthritis.Supported in part by funds from the Florida Chapter Arthritis Foundation and the Veterans Administration Medical Center.