SEM studies on the in vivo uptake of Aspergillus terreus spores by alveolar macrophages.
Pulmonary reactions to fungal spores constitute an important aspect of occupational pneumoconioses. Experimental models using aerosols of Aspergillus terreus spores produce an acute, complement dependent, hypoxic reaction in rabbits. The purpose of this study was to explore the possible role of the alveolar macrophage in initiating this reaction. Rabbits and rats were intratracheally injected with Aspergillus spores and the fate of the spores was studied at various times thereafter by light and scanning electron microscopy complemented by heavy metal staining and backscattered electron imaging. The uptake of spores by macrophages on the surface of the alveoli and airways was extremely rapid and was virtually complete by 3 hrs. Very few polymorphonuclear leukocytes were seen in the lungs of exposed animals. Penetration of the lung epithelium by spores was minimal and was not directly observed. Alveolar clearance followed by mucociliary clearance of the spores was observed in the rats. Failure of the clearance mechanisms at the level of the respiratory bronchiole produced necrotising lesions that contained numerous free spores. This study illustrates the value of heavy metal stains combined with backscattered electron imaging for observing surface and subsurface features in biological tissues.
D000818:Animals; D001230:Aspergillus / Q000472:pathogenicity*; D004195:Disease Models, Animal; D008264:Macrophages / Q000502:physiology*; D008297:Male; D008855:Microscopy, Electron, Scanning; D010587:Phagocytosis; D011009:Pneumoconiosis / Q000382:microbiology; D011650:Pulmonary Alveoli / Q000502:physiology*; D011817:Rabbits; D051381:Rats; D013172:Spores, Fungal / Q000472:pathogenicity*