Proteinase-induced modulation of the activity of rat macrophages to bind rabbit-IgG-sensitized sheep erythrocytes

Abstract

Rat alveolar and peritoneal macrophages were tested in a rosetting assay for their capacity to bind rabbit IgG antibody sensitized sheep erythrocytes (EA) before and after various times of incubation with proteolytic enzymes. With most enzymes, a biphasic effect on EA rosette formation was observed: an initial enhancement was followed by a reduction of the number of rosette-forming cells (RFC). The extent and rate of these changes depended on the type and concentration of the enzyme and on the amount of IgG antibodies used to sensitize the sheep erythrocytes. At low enzyme concentrations and with lowly sensitized EA, the phase of RFC enhancement was more prominent and prolonged. With an increase of enzyme concentration, the rate of reduction of RFC was increased. With regard to different enzymes, the highest rate of receptor degradation was found with pronase, followed by trypsin, whereas α-chymotrypsin had little receptor-degrading activity. A slight enhancement not followed by a loss of EA-rosetting activity was induced by granulocyte elastase at the concentrations studied. The results may give an explanation to contradicting reports in the literature, in which a single dose or just a few doses of proteolytic enzymes were employed and no kinetic studies were performed. In addition, EA-rosette-inhibiting material was found in supernatants of macrophage cultures, suggesting that receptor-like material was shed during incubation in serum-free medium. This material lost its EA-rosette-inhibiting capacity after proteinase treatment.