Secretion patterns of pro-MMP-9 and pro-MMP-2 to culture medium. (a) Representative gelatin-gel zymography showing enzymatic activities of proMMP-9 and proMMP-2 secreted to the culture medium by fetal membranes after selective infection with 1 × 106 CFU of E. coli. Each lysis band induced by pro-MMP-9 (b) and pro-MMP-2 (c) was quantified by densitometric analysis. Equal amounts of protein were loaded (0.5 μg). Each bar represents the mean and standard deviation of nine independent experiments; significant differences between basal and stimulated condition are indicated (*P < 0.05).