Heterogeneity of human lymphocyte Fc receptors. I. Differential susceptibility to proteolysis

Abstract

To study the possible heterogeneity of human lymphocyte Fc receptors, isolated human peripheral blood lymphocytes (PBL) were enzymatically altered (`stripped') by exposure to pronase or papain. Pronase treatment markedly increased the percentages of PBL binding IgG-sensitized erythrocytes (EA), while simultaneously removing or inactivating their receptors for heat-aggregated IgG (aggG). Papain treatment markedly diminished the ability of PBL to bind both EA and aggG. Essentially identical results were obtained utilizing EA composed of either human Rh-positive type O erythrocytes sensitized with the human anti-Rh serum Ripley (HRBC-A Ripley) or with chicken erythrocytes sensitized with rabbit anti-CRBC IgG (CRBC-A). CRBC sensitized with Fab'₂ fragments of rabbit anti-CRBC IgG were incapable of forming rosettes with normal or with pronase- or papain-stripped PBL. Pre-treatment of normal lymphocytes with aggG totally ablated their ability to rosette with EA.

Incubation of pronase-stripped PBL for 18–20 hr in 5% CO₂-air at 37°C resulted in diminution (to levels originally present) in the percentages of lymphocytes binding EA, but no regeneration of aggG receptors. Similar incubation of papain-stripped PBL resulted in significant reappearance of receptors binding EA, but no regeneration of aggG receptors. These results strongly suggest that: (1) lymphocyte receptors that bind EA complexes differ from those that bind aggG; (2) some lymphocytes possess cryptic receptors for EA that are expressed after proteolysis with pronase; (3) PBL having receptors for EA also have aggG receptors; and (4) there is no evidence that proteolytic stripping of PBL results in the generation of functionally different receptors for complexed IgG, since the Fc specificity of this receptor remains unchanged.