An extracellular connective tissue matrix, made up of components found in the pulmonary alveolar interstitium, was generated in vitro and used as a culture surface and substrate for proteolysis by human alveolar macrophages (AM) and neutrophil elastase (NE). The ability of human AM to modulate NE-mediated degradation of elastin and collagen in the surrounding matrix was studied to gain insights into the inflammatory process that accompanies the pathogenesis of emphysema in humans. Neutrophil elastase that had been internalized by AM showed a diminished but more prolonged time course of matrix proteolysis than did a similar amount of NE added to the matrix in the absence of AM. Collagen and elastin degradation were quantitated by release of hydroxylysine and desmosine, respectively, into the culture medium. Significantly more hydroxylysine and desmosine were released by AM that had internalized NE than by AM or by culture medium alone. When 14 X 10(6) AM were added to the extracellular matrix, followed 2 h later by addition of 2 micrograms of NE, collagen and elastin degradation measured at 24 h were not significantly different from that which occurred when matrix was incubated with NE in the absence of AM. Collagen degradation, determined in the same cultures during the period from 24 to 96 h, was significantly greater when matrix was incubated with both AM and NE. These findings suggest that AM can release previously internalized NE in an enzymatically active form and that AM may enhance collagen degradation in matrix that was also exposed to NE.