Our data suggest that Ureaplasma species or serovars are not intrinsically “virulent” or “avirulent,” but instead that variation of the ureaplasma MBA protein may play an important role in modulating the immune response: when MBA/mba size variation occurred in vivo there was a decrease in the incidence of chorioamnionitis and lower levels of the cord blood cytokines IL-8 and G-CSF. Here, CSF3 is linked to chorioamnionitis.