Immunoblot for matrix metalloprotease (MMP)-3. Media were harvested after 5, 10, 15 and 21 days under control conditions and, after five days, in the presence of neutrophil elastase (NE) and subjected to immunoblot for MMP-3. (a) Human fetal lung (HFL) fibroblasts alone. (b) Blood monocytes (BM) co-cultured with HFL fibroblasts. The latent 57 kDa form of MMP-3 is shown; addition of NE for the first five days resulted in conversion of the 57 kDa form to active 47 kDa and 35 kDa forms. Lane 1: samples were harvested on day 5. Lane 2: culture medium in the presence of NE, harvested at day 5. Lanes 3, 4, 5: samples harvested on days 10, 15 and 21 under control conditions, respectively. (c) BM alone.