In vitro interaction of alveolar macrophages and Aspergillus fumigatus.

In vitro interaction of alveolar macrophages (AM) from rats with conidia from Aspergillus fumigatus and Aspergillus candidus as well as inert control particles (amorphous silica) of similar diameter (about 3 microns), was studied. Experimental observations showed that both kinds of conidia were phagocytized significantly faster by AM than were the control particles due to a faster rate of attachment, but even more so due to a faster rate of ingestion. Quantitative nitroblue tetrazolium reduction by AM reflecting their oxidative metabolism and oxygen radical release was increased in response to both kinds of conidia by a factor of 2-3 during the process of phagocytosis, as well as 24 hr after the onset of phagocytosis, compared to corresponding conditions with inert particles and to resting macrophages. The mean pH in phagolysosomes with each of the conidia tended to be higher after 3 hr but was significantly lower after 24 hr than in the phagolysosomes with the control particles. After 3 hr there was a considerable percentage (around 8%) of phagolysosomes with pH > or = 6.5 and after 24 hr there was still a small percentage (0.7%) of such phagolysosomes for each of the conidia. Such a fraction was not observed for the control particles. Electron microscopic studies showed passages between phagolysosomes and AM surface with both kinds of conidia. The occurrence of such unsealed phagolysosomes might explain the percentage of phagolysosomes with high pH. Hence, Aspergillus conidia in unsealed macrophage vacuoles mediate an increased oxygen radical release from the macrophages, a process which in the long run might cause lung damage.