Abstract
Monolayers of freshly isolated human monocytes are known to ingest particulate activators of the human alternative complement pathway. The ingestion of rabbit erythrocytes, E R, by human monocytes in serum-free medium was studied. The process is Mg 2+-dependent and optimum phagocytic activity was obtained at ~20 m M MgCl 2. Preincubation of mononuclear leukocytes increased the number of monocytes ingesting E R by at least twofold and this involved de novo protein synthesis, as evidenced by inhibition with cycloheximide. However, preincubation of the mononuclear leukocytes for longer periods (>4 hr) caused a decrease in the percentage of ingesting monocytes. No inhibition of ingestion of E R was observed by cobra venom factor (CVF) or F(ab′) 2 rabbit anti-human C3 or F(ab′) 2 murine monoclonal anti-human Bb, known to inhibit C3 convertase activity. The ingestion was also not inhibited by (a) rabbit anti-human CR1, (b) OKM1 or anti-MO1, two monoclonal anti-CR3 antibodies, (c) goat anti-human IgG F c receptor, or (d) mannan, a competitive inhibitor of ligand uptake by the mannosyl-fucosyl receptor (MFR). In contrast, ingestion was inhibited by glucan particles of yeast.
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