Choriodecidual Group B Streptococcal Inoculation Induces Fetal Lung Injury without Intra-Amniotic Infection and Preterm Labor in Macaca nemestrina

Abstract

BackgroundEarly events leading to intrauterine infection and fetal lung injury remain poorly defined, but may hold the key to preventing neonatal and adult chronic lung disease. Our objective was to establish a nonhuman primate model of an early stage of chorioamnionitis in order to determine the time course and mechanisms of fetal lung injury in utero.Methodology/Principal FindingsTen chronically catheterized pregnant monkeys (Macaca nemestrina) at 118–125 days gestation (term = 172 days) received one of two treatments: 1) choriodecidual and intra-amniotic saline (n = 5), or 2) choriodecidual inoculation of Group B Streptococcus (GBS) 1×106 colony forming units (n = 5). Cesarean section was performed regardless of labor 4 days after GBS or 7 days after saline infusion to collect fetal and placental tissues. Only two GBS animals developed early labor with no cervical change in the remaining animals. Despite uterine quiescence in most cases, blinded review found histopathological evidence of fetal lung injury in four GBS animals characterized by intra-alveolar neutrophils and interstitial thickening, which was absent in controls. Significant elevations of cytokines in amniotic fluid (TNF-α, IL-8, IL-1β, IL-6) and fetal plasma (IL-8) were detected in GBS animals and correlated with lung injury (p<0.05). Lung injury was not directly caused by GBS, because GBS was undetectable in amniotic fluid (∼10 samples tested/animal), maternal and fetal blood by culture and polymerase chain reaction. In only two cases was GBS cultured from the inoculation site in low numbers. Chorioamnionitis occurred in two GBS animals with lung injury, but two others with lung injury had normal placental histology.Conclusions/SignificanceA transient choriodecidual infection can induce cytokine production, which is associated with fetal lung injury without overt infection of amniotic fluid, chorioamnionitis or preterm labor. Fetal lung injury may, thus, occur silently without symptoms and before the onset of the fetal systemic inflammatory response syndrome.

Animal models of bronchopulmonary dysplasia. The preterm baboon models

“…These findings are consistent with recent evidence that 35% of umbilical cord blood specimens from human infants born at 23-to 28-wk gestation are culture positive for Ureaplasma species and/or M. hominis and are associated with a neonatal systemic inflammatory response (29). The importance of perinatal infection on lung development and injury are further supported by studies with Group B Streptococcus in pregnant, preterm Rhesus demonstrating fetal lung injury and disturbed morphogenesis/angiogenesis, even when fulminant infection is not present (1,48).…”

Choriodecidual Group B Streptococcal Infection Induces miR-155-5p in the Fetal Lung in Macaca nemestrina

“…All surgery was performed while the animals were under general anesthesia, and all efforts were made to minimize suffering. A description of the chronically catheterized pregnant nonhuman primate model of choriodecidual GBS infection, including details on animal care, analgesia, surgery, fetal euthanasia and necropsy, and fetal lung pathology and scoring, has been previously reported (12,15). Briefly, 10 chronically catheterized pregnant nonhuman primates (Macaca nemestrina) at 118 to 125 days of gestation (term ϭ 172 days) received one of two experimental treatments: (i) choriodecidual and intra-amniotic fluid saline infusions (the saline control group, n ϭ 5) or (ii) GBS choriodecidual inoculations (the GBS group; n ϭ 5).…”

“…Briefly, 10 chronically catheterized pregnant nonhuman primates (Macaca nemestrina) at 118 to 125 days of gestation (term ϭ 172 days) received one of two experimental treatments: (i) choriodecidual and intra-amniotic fluid saline infusions (the saline control group, n ϭ 5) or (ii) GBS choriodecidual inoculations (the GBS group; n ϭ 5). Both choriodecidual and intra-amniotic fluid saline infusions were used to confirm that neither inoculation was associated with increased AF cytokine levels and were described previously (12). Intraamniotic fluid pressure was continuously recorded, digitized, and analyzed as reported previously (12).…”

“…Both choriodecidual and intra-amniotic fluid saline infusions were used to confirm that neither inoculation was associated with increased AF cytokine levels and were described previously (12). Intraamniotic fluid pressure was continuously recorded, digitized, and analyzed as reported previously (12). Preterm labor was defined as an intraamniotic fluid pressure of 10,000 mm Hg · s/h in association with a change in cervical effacement or dilation.…”

“…Our previous studies using a pregnant nonhuman primate model revealed that early choriodecidual GBS infection elevated inflammatory cytokine levels in the amniotic fluid (AF) and induced fetal lung injury (11,12). Interestingly, despite observations of fetal lung injury and preterm labor (in some cases), bacteria did not translocate into AF or fetal tissues in any of the GBS-infected animals (12). However, differential gene expression was observed in the injured fetal lungs of GBS-infected animals and included the downregulation of pathways involved in angiogenesis and morphogenesis (11).…”