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

We used ultrastructural and immunocytochemical technique to follow the movement ofhuman neutrophil elastase (HNE) and porcine pancreatic elastase (PPE) through aliving extracellular matrix produced by cultured smooth muscle cells and to comparethe effect of the two elastases on elastic fibers in situ. Although both enzymessolubilize elastin purified from these cultures at similar rates, PPE solubilized11.5 times more elastin from the intact cultures than did HNE. The difference in therate of elastin solubilization from the cultures parallels the degree of elasticfiber degradation and the emphysema-inducing potency of the two elastases when theyare instilled into animal lungs. Immunohistochemical studies employing antibodies toHNE and PPE revealed that PPE penetrates the smooth muscle cell cultures more readilythan does HNE. Because the amount of elastin in these cultures increases withincreasing distance from the free surface, the lesser amounts of elastin solubilizedby HNE may be partly due to poor penetration of HNE into the living extracellularmatrix, resulting in limited access to elastin substrate. Ultrastructural andimmunocytochemical studies indicated, however, that even when HNE does have access toelastin substrate, it is less efficient than PPE at penetrating and degradingindividual elastic fibers.