Clathrin-coated pit-associated proteins are required for alveolar macrophage phagocytosis

During phagocytosis, phagocytic receptors and membrane material must be ins erted in the pseudopod membrane as it extends over the phagocytic target. T his may require a clathrin-mediated recycling mechanism similar to that pos tulated for leading edge formation during cell migration, To investigate th is possibility, liposomes were used to deliver to intact rat alveolar macro phages (AMs): 1) Abs to clathrin, clathrin adaptor AP-2, and hsc70, and 2) amantadine, Phagocytosis was assayed by fluorometric and colorimetric techn iques, Liposome-delivered Abs to clathrin and AP-2 inhibited AM phagocytosi s of zymosan-coated, fluorescent liposomes from 16.3 +/- 0.3 to 5.8 +/- 0.3 , and 10.1 +/- 0.9 to 4.8 +/- 0.2 liposomes/cell (p < 0.01). Similarly, lip osome-delivered Ab to clathrin also inhibited AM phagocytosis of IgG-opsoni zed RBCs from 11.7 +/- 1.7 to 3.8 +/- 0.7 RBCs/cell (p < 0.01), Amantadine, which blocks the budding of clathrin-coated vesicles, inhibited phagocytos is from 13.8 +/- 0.8 to 5.7 +/- 0.6 (p < 0.01), Ab blockade of hsc70, which catalyzes clathrin turnover, also inhibited phagocytosis from 9.1 +/- 0.5 to 4.3 +/- 0.2 (p < 0.01). These findings suggest that clathrin-mediated re ceptor/membrane recycling is required for phagocytosis.