Interleukin 18 messenger RNA and proIL-18 protein expression in chorioamniotic membranes from pregnant women with preterm prelabor rupture of membranes.

OBJECTIVE To quantify the expression of IL-18 mRNA and protein in the chorioamniotic membranes of pregnant women with PPROM and correlate expression with histological chorioamnionitis. STUDY DESIGN A case control study that included 42 pregnant women not in labor in the following groups: PPROM (n=28) and controls with intact membranes submitted to selective cesarean section at term (n=14). Expression of IL-18 mRNA in chorioamniotic membranes was determined by real-time polymerase chain reaction, and IL-18 protein expression was measured by western blot. Histopathological analyses and immunolocalization of IL-18 by immunohistochemistry were also performed. Analyses were performed using the Mann-Whitney or Fisher's exact tests and the group effect was considered significant if the adjusted p-values were <0.05 and the magnitude of change was greater than 2-fold for mRNA expression. RESULTS IL-18 mRNA was present in 100% of samples and no difference in expression was observed between term vs. PPROM membranes (fold-change 0.12; p=0.88). In the PPROM group, no difference was observed in IL-18 mRNA regarding gestational age (fold-change 0.11; p=0.42) or the presence of histological chorioamnionitis (fold-change 0.26; p=0.15). ProIL-18 was present in all samples. IL-18 was immunolocalized to amnion, chorion and decidua cells, with intense immunohistochemical staining at the choriodecidual junction. CONCLUSION Chorioamniotic membranes are sources of IL-18 mRNA and proIL-18, and their expression is unrelated to PPROM or histological chorioamnionitis.