Lung injury induced by mycobacterial cell walls: Effects on connective tissue

Intravenous injection of cell walls from Mycobacterium bovis strain BCG results in increased lung mass in the rat 4 months after injection. Histologically, there is a simultaneous increase in interstitial material and the formation of granulomata. The granulomata do not show increased staining for collagen by a trichrome stain. Prominent reticulin is present in the granulomata as shown by a silver stain. Lung dry weight is significantly increased 4 months after the injection of 300 μg cell walls; the total amount of collagen is significantly increased, but its concentration (amount per mg dry weight) is similar to that of controls. At 6 months, lung collagen amounts in BCG-treated animals are not significantly different from those of controls. By 10 months the granulomata largely disappear, lung architecture returns to normal, and lung collagen amounts are at control levels. In this model of lung injury, increases in lung connective tissue proteins are not selective and they do not persist as the lung returns to normal histologically.