IN-VIVO INTERACTION BETWEEN ALVEOLAR MACROPHAGES AND CRYPTOCOCCUS-NEOFORMANS

In vivo interactions of rabbit alveolar macrophages (AM) and Cryptococ cus neoformans, a yeast pathogenic for humans, were studied. Bs a cont rol, inert silica particles of a similar diameter (5-6 mu m) were used . Of 16 rabbits, 6 were instilled intratracheally with fluorescein-lab elled heat-killed C. neoformans, 6 with fluorescein-labelled silica pa rticles and 4 with saline only. After 24 h, the AM were collected by l ung lavage, and phagocytosis, oxidative metabolism, phagolysosomal pH and morphology were studied. The accumulated number of yeasts attached to the AM was almost the same for C. neoformans as for the silica par ticles. The ingested fraction of C. neoformans was even higher than th at of the silica particles. Quantitative NET reduction by the AM, refl ecting their oxidative metabolism, was markedly increased by exposure to C. neoformans for 24 h. The phagolysosomal pH was on the average lo wer in phagolysosomes with C. neoformans than with the silica particle s, although approximately 2% of the phagolysosomes with C. neoformans had neutral pH. Phagolysosomes with neutral pH was not observed for si lica particles. Electron microscopy showed presence of C. neoformans i n phagolysosomes of AM. The conclusion of this study is that the phago cytic activity, oxidative metabolism and phagolysosomal pH AM against C. neoformans are significant 24 h after the exposure.