Abstract
A method is described to study quantitatively and rapidly the kinetics of endocytosis of a receptor-bound ligand by cells of various subclasses within a heterogeneous cell population. The time course of the internalization of the bound ligand is followed by labeling, with a fluorescent antibody, the ligand molecules exposed on the cell surface at various times of the endocytosis process, and by measuring with a flow cytofluorometer the fluorescence of a large number of individual cell within the total cell population. A convenient mathematical treatment of the data is proposed for analyzing the experimental results. This method is applied to the kinetic study of the endocytosis of rabbit antibodies (anti-mouse immunoglobulin) by B-lymphocytes within a mouse spleen cell suspension.