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Background: The multiple banded antigen (MBA), a surface-exposed lipoprotein, is a proposed virulence factor of Ureaplasma spp. We previously demonstrated that the number of Ureaplasma parvum MBA size variants in amniotic fluid was inversely proportional to the severity of chorioamnionitis in experimentally infected pregnant sheep. However, the effect of ureaplasma MBA size variation on inflammation in human pregnancies has not been reported. Methods: Ureaplasmas isolated from the chorioamnion of pregnant women from a previous study (n = 42) were speciated/serotyped and MBA size variation was demonstrated by PCR and western blot. Results were correlated with the severity of chorioamnionitis and cord blood cytokines. In vitro, THP-1-derived macrophages were exposed to recombinant-MBA proteins of differing sizes and NF-κB activation and cytokine responses were determined. Results: MBA size variation was identified in 21/32 (65.6%) clinical isolates (in 10 clinical isolates MBA size variation was unable to be determined). Any size variation (increase/decrease) of the MBA (regardless of Ureaplasma species or serovar) was associated with mild or absent chorioamnionitis (P = 0.023) and lower concentrations of cord blood cytokines IL-8 (P = 0.04) and G-CSF (P = 0.008). In vitro, recombinant-MBA variants elicited different cytokine responses and altered expression of NF-κB p65. Conclusion: This study demonstrates that size variation of the ureaplasma MBA protein modulates the host immune response in vivo and in vitro.

Background: Ureaplasmas are the most prevalent bacteria isolated from preterm deliveries and the prognosis for neonates varies depending on the gestation at delivery. Ureaplasmas vary their surface-exposed antigen (MBA, a virulence mechanism) during chronic intra-amniotic infections, but it is not known when changes first occur during gestation. Method: U. parvum serovar 3 (2x10e7CFU) was injected intra-amniotically (IA) into six experimental cohorts of pregnant ewes (of n=7), 3 days (d) or 7d before delivery at either: 100d, 124d or 140d gestation (term=145d). Control ewes received IA 10B broth. Fetuses were delivered surgically and ureaplasmas cultured from amniotic fluid (AF), chorioamnion, fetal lung (FL) and umbilical cord. Ureaplasmas were tested by western blot to demonstrate MBA variation. Results: The highest number of ureaplasmas were recovered from FL at 100d gestation after 3 days of infection (p

Background: Ureaplasma species are the most prevalent isolates from women who deliver preterm. The MBA, a surface exposed lipoprotein, is a key virulence factor of ureaplasmas. We investigated MBA variation after chronic and acute intra-amniotic (IA) ureaplasma infections. Method: U. parvum serovar 3 (2x104 colony-forming-units) was injected IA into pregnant ewes at: 55 days gestation (d, term = 145d) (n=8); 117d (n=8) and 121d (n=8). Fetuses were delivered surgically (124d) and ureaplasmas cultured from amniotic fluid (AF), chorioamnion, fetal lung (FL) and umbilical cord were tested by western blot and PCR assays to demonstrate MBA and mba gene variation respectively. Tissue sections were sectioned and stained by haemotoxylin and eosin and inflammatory cell counts and pathology were reported (blinded to outcome). Results: Numerous MBA/mba variants were generated in vivo after chronic exposure to ureaplasma infection but after acute infection no variants (3d) or very few variants (7d) were generated. Identical MBA variants were detected within the AF and FL but different ureaplasma variants were detected within chorioamnion specimens. The severity of inflammation within chronically infected tissues varied between animals ranging from no inflammation to severe inflammation with/without fibrosis. Chorioamnion, FL and cord from the same animal demonstrated the same degree of inflammation. Conclusions: MBA/mba variation in vivo occurred after the initiation of the host immune response and we propose that ureaplasmas vary the MBA antigen to evade the host immune response. In some animals there was no inflammation despite colonisation with high numbers of ureaplasmas.