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.