Immunocytochemical study of the degradation of elastic fibers in a living extracellular matrix.

We used ultrastructural and immunocytochemical technique to follow the movement of human neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) through a living extracellular matrix produced by cultured smooth muscle cells and to compare the effect of the two elastases on elastic fibers in situ. Although both enzymes solubilize elastin purified from these cultures at similar rates, PPE solubilized 11.5 times more elastin from the intact cultures than did HNE. The difference in the rate of elastin solubilization from the cultures parallels the degree of elastic fiber degradation and the emphysema-inducing potency of the two elastases when they are instilled into animal lungs. Immunohistochemical studies employing antibodies to HNE and PPE revealed that PPE penetrates the smooth muscle cell cultures more readily than does HNE. Because the amount of elastin in these cultures increases with increasing distance from the free surface, the lesser amounts of elastin solubilized by HNE may be partly due to poor penetration of HNE into the living extracellular matrix, resulting in limited access to elastin substrate. Ultrastructural and immunocytochemical studies indicated, however, that even when HNE does have access to elastin substrate, it is less efficient than PPE at penetrating and degrading individual elastic fibers.