Ingestion of Giardia lamblia trophozoites by human mononuclear phagocytes.
Mononuclear phagocytes may be important effector cells against Giardia lamblia. Human monocyte-derived macrophages were incubated with G. lamblia trophozoites in 13% heat-inactivated autologous serum. At a G. lamblia/macrophage ratio of 1:1, the number of trophozoites ingested per 100 macrophages ranged from 1 to 12 at 0.5 h and increased for all donors (n = 6) to 10 to 92 at 8 h. Ingestion was confirmed by electron microscopy. Increasing the parasite/phagocyte ratio to 5:1 increased the percentage of macrophages with adherent but not ingested trophozoites. Incubating Giardia cells and macrophages with 20% immune serum increased ingestion of parasites eightfold, indicating that anti-G. lamblia antibody can enhance ingestion. Both phase-contrast microscopy and electron microscopy documented trophozoite destruction within macrophages. Ingestion of parasites elicited an oxidative burst as measured by luminol-enhanced chemiluminescence. In vitro, Giardia trophozoites were killed by greater than or equal to 5 X 10(-5) M H2O2. Fusion of lysosomes with parasite-containing phagosomes was suggested by acridine orange-stained preparations. Human macrophages have the capacity to ingest Giardia trophozoites and to kill intracellular parasites, possibly by oxidative microbicidal mechanisms.
Hill
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DR
Department of Medicine, University of Connecticut School of Medicine, Farmington 06032.
Pearson
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RD
D000818:Animals; D005872:Giardia / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000633:toxicity; D066298:In Vitro Techniques; D008163:Luminescent Measurements; D008264:Macrophages / Q000469:parasitology / Q000502:physiology*; D008854:Microscopy, Electron; D010101:Oxygen Consumption; D010587:Phagocytosis
D006861:Hydrogen Peroxide