ALVEOLAR MACROPHAGE RESPONSE TO YEASTS AND INERT PARTICLES

Interactions between alveolar macrophages (AM) from rats and a yeast w ith relatively high pathogenicity (Candida albicans), a yeast with low pathogenicity (Saccharomyces cerevisiae) and an inert control particl e (amorphous silica) of similar diameters, 3-4 mu m, were studied. Bot h yeasts were phagocytized significantly faster by AM than were the co ntrol particles and C. albicans significantly faster than S. cerevisia e. Quantitative nitroblue tetrazolium reduction by AM reflecting their oxidative metabolism was markedly increased in response to both fungi during the period of phagocytosis as well as 24 h after the phagocyto sis. Macrophages with silica particles also showed a moderate but sign ificant increase in oxidative metabolism 24 h after phagocytosis. Phag olysosomal pH was significantly higher for S. cerevisiae than the cont rol particles after 3 and 24 h. pH in phagolysosomes with C. albicans tended to be higher after 3 h but was significantly lower after 24 h t han in the phagolysosomes with silica particles. Both yeasts showed a considerable number (around 10%) of phagolysosomes with high pH greate r than or equal to 6.5 after 3 h and a smaller percentage after 24 h. No such fraction could be seen for the control particles. Electron mic roscopy showed narrow passages from AM cell surface to phagolysosomes with particles. These passages might be more frequent in AM containing the yeasts and could explain the phagolysosomes with high pH.