FIG. 5.

Cell surface enzyme is responsible for the degradation of substrates by cells. (A) Confluent HGF (donor, MH-12) were stimulated with IL-1α (10 ng/ml) for 6 days in α-MEM supplemented with 10% FCS in 96-well plates and then washed with PBS three times, and confluent-monolayer cells were examined by DPPIV assay. Monolayer cells were incubated with 2 mM substrate for DPPIV assay as described in Materials and Methods. After a 60-min incubation, the supernatant and the corresponding monolayer cells, which were resuspended in peptidase medium, were incubated for an additional 90 min without addition of the substrate. □, pNA formed by intact fibroblasts; ◊, pNA formed by supernatant resulting from 60 min of preincubation of cells with the substrate; ○, pNA released by cells preincubated for 60 min with the substrate. (B) The percentage of lysed fibroblasts was determined by trypan blue exclusion at each time point. The results are representative of three different experiments with three different donors (MH-12, KEK, and NIK).