Release of Mycoplasma pneumoniae substances after phagocytosis by guinea pig alveolar macrophages

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Abstract
Antibody-opsonized Mycoplasma pneumoniae cells with various radioactive markers were sedimented onto monolayers of guinea pig alveolar macrophages (AM). After 2 h of incubation, about 50% of the activity of [3H]palmitate-labeled mycoplasmas was associated with AM. Nonspecific attachment of the opsonized mycoplasmas to AM-free plastic surface areas was negligible. The occurrence of phagocytosis was proven by electron microscopy and monitoring of AM surface-bound antigen by 125I-labeled F(ab)2 fragments. The activity of [3H]palmitic acid-labeled mycoplasmas was only slowly released into the supernatant. About 55% of the activity remained AM-associated up to 70 h after phagocytosis. After phagocytosis of [3H]thymidine-labeled cells, about 70% of the radioactivity found non-precipitable by trichloracetic acid. 3H-amino acid-labeled protein was released to 50% within 8 h. Supernatants and AM were tested for M. pneumoniae antigen with enzyme-linked immunosorbent assay. Considerable amounts of antigenically active material could be found in the supernatant within 8 h. This antigen was totally inactivated by heat (80 degrees C). Trypsin treatment (1 mg/ml, 10 min) reduced the antigenicity by 80%. The results suggest a selective release of microbial material after phagocytosis.