In vitro sequestration of erythrocytes from hosts of various ages

Abstract

Erythrocytes from young and old human donors were separated according to age-density on Stractan gradients. Old donors had more low age-density (young) erythrocytes than did young donors. Levels of IgG bound to old and young erythrocytes were determined by ELISA. Erythrocytes from old donors bore higher levels of IgG on their erythrocytes (123 +/- 55 IgG molecules per young RBC and 196 +/- 43 IgG per old RBC) than did those from young donors (58 +/- 15 IgG per young RBC and 98 +/- 20 IgG per old RBC). In an in vitro erythrophagocytosis assay, young and old erythrocytes from old donors and old erythrocytes from young donors were shown to be recognized and phagocytosed by lymphokine activated human peripheral blood monocytes. Young erythrocytes from young donors were not phagocytosed in this assay. The in vitro erythrophagocytosis of erythrocytes from old and young donors can be specifically blocked by beta-galactoside but not alpha-galactoside sugars. This phagocytosis is not blocked by Protein-G which specifically blocks Fc-gamma mediated erythrophagocytosis of Rh-D+ erythrocytes coated with IgG anti-Rh-D antibodies. beta-galactoside and alpha-galactoside sugars have no inhibitory effect on erythrophagocytosis mediated by IgG anti-Rh-D antibodies coating Rh-D+ erythrocytes. It thus appears that erythrophagocytosis of young and old erythrocytes from old donors and old erythrocytes from young donors are all mediated by a lectin-like receptor on the monocytes which recognizes beta-galactoside-like sugar moiety on the erythrocytes rather than by recognition of IgG on the erythrocyte and an Fc receptor on the macrophage. It also appears that the membrane of both young and old erythrocytes of old donors are marked for phagocytosis whereas only the old erythrocytes from young donors are so marked.