Variants that lack the ability to ingest latex beads were isolated from the mouse macrophagelike cell line J774. Carboxylated latex beads were derivatized with polylysine and then daunomycin by a carbodiimide method. Cells that ingested such beads were killed; variants that survived were isolated. Variants were detected at very low frequency and only after nitrosoguanidine mutagenesis. Of 11 independent isolates, 10 showed a lowered rate of uptake of polystyrene beads (without daunomycin). All of these proved normal in rate and extent of Fc-mediated phagocytosis. There was essentially no change in sensitivity to free daunomycin in the variants compared to the parent. These results support the previous hypothesis that there are differences in the metabolic routes of receptor-mediated and nonspecific phagocytosis.

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