Ultrastructural analysis of the pneumocyte-interstitium boundary line in the course of enzymatic lung injury.

The studies were performed basing on the experimental model of acute pulmonary tissue injury. Papain in a dose of 2 mg/ml PBS/100 g b.w. was administered once, intratracheally, on the 21st day of the experiment. Besides, female Wistar rats were injected twice with BCG vaccine in a dose of 4 x 10(8) microorganisms. BCG vaccine was administered intraperitoneally on the 1st and 14th day of the experiment to activate the system of mononuclear phagocytes. Control rats were intratracheally or/and intraperitoneally given PBS solution. All the animals were killed on the 28th, 35th and 42nd day of the experiment. A single intratracheal papain injection induced emphysematous changes in the animal lungs. The changes were accompanied by basement membrane rebuilding and focal collagen and elastin cumulation. An increase in the number of type II alveolar epithelial cells was observed. Anchorage of collagen fibres and microfibrillary structures in the cytoplasm of type II pneumocytes was observed in the BCG- and papain-treated animals. There, the cytoplasmic membrane of type II cells was completely indistinct and the cytoplasm formed processes to penetrate into the connective tissue fibres. The results obtained indicate possible contribution of type II pneumocytes to fibroplasia processes during lung parenchyma rebuilding and suggest the necessity to include fibroplasia elements in the existing definition of emphysema.