Evidence for intracellular digestion of an exogenous protein by rat peritoneal macrophages.

The differential effects of lower incubation temperature on the digestion of formaldehyde-denatured 125I-labelled bovine serum albumin by intact rat peritoneal macrophages and by macrophage homogenates were studied. Digestion by intact macrophages was abolished at 20 degrees C and below, but a near-linear relationship between digestion rate and temperature between 37 degrees C and 5 degrees C was found with homogenates. Several known inhibitors of pinocytosis were found to inhibit the generation of digestion products from 125I-labelled albumin by macrophages. It is concluded that pinocytosis is an obligatory step in the catabolism of exogenous proteins by macrophages.