Background: Microbial infection of the amniotic cavity is a major cause of early preterm birth. Ureaplasma spp. are the most commonly isolated microorganism isolated from amniotic fluid and placental tissues of preterm deliveries, and bacteria most commonly associated with vigorous intraamniotic inflammation . Ureaplasma spp. are genitourinary tract commensals, colonising around 50% of pregnant women; however, an estimate of <1% of pregnancies are complicated by Ureaplasma-associated infection/inflammation. Our aim was to determine the rate and extent of penetration of Ureaplasma parvum serovar 3 (UpSV3) infection through human placental membranes and assess the corresponding inflammatory cytokine response, using a two-compartment perfusion model employing human extraplacental membranes.
Method: Full thickness membranes (amnion and choriodecidua) were collection from term elective Caesarean section deliveries (n=4). Membranes were secured over Transwell inserts and placed in a 6 well tissue culture dish containing either culture media (maternal face) or artificial amniotic fluid (fetal face). Transwells were inoculated with 106 CFU/mL UpSV3 and incubated for 1, 6, 12, 24 and 48 h (5%CO2/2%O2). Media from the inner and outer chambers were collected for determination of IL-1b, IL-6 and IL-8 concentrations by MagPix assay. Membranes were either embedded for immunohistochemical staining, or separated into amnion and choriodecidua for quantitation of UpSV3 DNA by qPCR.
Results: IL-1b concentrations increased with time in both amnion and choriodecidual compartments, reaching significance at 24 h (p<0.05, ANOVA). IL-8 levels showed non-significant trend towards increases with UpSV3 infection, while IL-6 levels showed inconsistent responses. UpSV3 DNA was abundant in the amnion, less so in choriodecidua, with amounts increasing with incubation time. UpSV3 was detected in the tissues by immunofluorescence, with staining patterns confirming the qPCR data.
Conclusion: Intra-amniotic UpSV3 infection progressively penetrates the fetal and maternal membranes over 48 h, eliciting a delayed inflammatory response characterised by increased IL-1b production. The findings from this model add and further clarify our understanding of the pathophysiology of infection-driven preterm birth.