The Severity of Chorioamnionitis in Pregnant Sheep Is Associated with In Vivo Variation of the Surface-Exposed Multiple-Banded Antigen/Gene of Ureaplasma parvum1

Abstract

Ureaplasma species are the bacteria most frequently isolated from human amniotic fluid in asymptomatic pregnancies and placental infections. Ureaplasma parvum serovars 3 and 6 are the most prevalent serovars isolated from men and women. We hypothesized that the effects on the fetus and chorioamnion of chronic ureaplasma infection in amniotic fluid are dependent on the serovar, dose, and variation of the ureaplasma multiple-banded antigen (MBA) and mba gene. We injected high- or low-dose U. parvum serovar 3, serovar 6, or vehicle intra-amniotically into pregnant ewes at 55 days of gestation (term = 150 days) and examined the chorioamnion, amniotic fluid, and fetal lung tissue of animals delivered by cesarean section at 125 days of gestation. Variation of the multiple banded antigen/mba generated by serovar 3 and serovar 6 ureaplasmas in vivo were compared by PCR assay and Western blot. Ureaplasma inoculums demonstrated only one (serovar 3) or two (serovar 6) MBA variants in vitro, but numerous antigenic variants were generated in vivo: serovar 6 passage 1 amniotic fluid cultures contained more MBA size variants than serovar 3 (P = 0.005), and ureaplasma titers were inversely related to the number of variants (P = 0.025). The severity of chorioamnionitis varied between animals. Low numbers of mba size variants (five or fewer) within amniotic fluid were associated with severe inflammation, whereas the chorioamnion from animals with nine or more mba variants showed little or no inflammation. These differences in chorioamnion inflammation may explain why not all women with in utero Ureaplasma spp. experience adverse pregnancy outcomes.

The Human Ureaplasma Species as Causative Agents of Chorioamnionitis

“…These data demonstrate that Ureaplasma can chronically colonize the amniotic fluid for at least 85 days and suggest that amniotic fluid, a rich source of urea, can support the long-term growth of these microorganisms. We further demonstrated that U. parvum was consistently isolated from the chorioamnion and fetal lung following chronic intra-amniotic infection (205,215,(218)(219)(220) and was also isolated from the umbilical cord and other fetal tissues, including cerebrospinal fluid, gut, kidney, liver, and spleen (205). These findings are consistent with human studies that have reported that Ureaplasma spp.…”

“…However, these findings are not always consistent, with a recent study by our group demonstrating no correlation between the numbers of Ureaplasma present within placentae, the species/serovar present, or the ethnicity of women infected with Ureaplasma and the incidence or severity of histological chorioamnionitis (62). Furthermore, animal model studies in which Ureaplasma infections have been established with the same strain and dose of U. parvum resulted in divergent inflammatory responses within the chorioamnion (59,205,206) and within other genital tract tissues (207), suggesting that the development or magnitude of host immune responses may contribute to the severity of chorioamnionitis. Indeed, we have demonstrated that the human Ureaplasma spp.…”

“…Intra-amniotic U. parvum infection was also associated with increased expression of IL-1␤, IL-6, and IL-8 mRNA within the chorioamnion (59,219) and an influx of neutrophils, monocytes/ macrophages, and lymphocytes (59,205,218), compared to medium (vehicle) controls. Generally, the severity of chorioamnionitis correlated with increased duration of intraamniotic Ureaplasma exposure (206); however, variability in the severity of inflammation was a notable feature of these sheep studies (205,206), consistent with findings from human pathological investigations. Despite 100% of chorioamnion samples being infected with U. parvum, the severity of chorioamnionitis ranged from moderate (characterized by inflammatory cell infiltrate, fibrosis, scarring, sloughing of the amnion epithelium, and disruption of the normal tissue architecture) to no histological evidence of chorioamnionitis (205).…”

“…We have demonstrated that human U. parvum clinical isolates injected into the amniotic cavity of pregnant sheep at 55 days (term is 150 days) can chronically colonize the amniotic fluid and fetus (59,205,215,218). Following an intra-amniotic injection of 2 ϫ 10 4 CFU of U. parvum serovar 6 at 55 days of gestation, temporal analysis demonstrated that the peak of amniotic fluid infection occurred between 87 days and 101 days of gestation and that the number of CFU per milliliter remained high (approximately 10 7 CFU/ml) until the time of surgical delivery at 140 days (59).…”

“…Both chronic and acute intrauterine Ureaplasma infections were capable of causing histological chorioamnionitis in pregnant sheep (59,205,206,218,219). Intra-amniotic U. parvum infection was also associated with increased expression of IL-1␤, IL-6, and IL-8 mRNA within the chorioamnion (59,219) and an influx of neutrophils, monocytes/ macrophages, and lymphocytes (59,205,218), compared to medium (vehicle) controls.…”