Uptake of ¹²⁵I-labeled rGCR by rat alveolar macrophages at 37°C. (A) The concentration of¹²⁵I-labeled pGCR specifically bound to mannose receptors plotted as a function of time after incubation with 1.5 (▪), 3 (▴), and 6 (⧫) nmol/L ¹²⁵I-labeled pGCR. (B) The binding of 6 nmol/L ¹²⁵I-labeled pGCR to rat alveolar macrophages in the presence (⧫) and absence (▪) of yeast mannan, and the specific mannose receptor-mediated binding and/or uptake (▴), plotted as a function of time.