The presence of microbes in the intrauterine compartment during pregnancy has traditionally been investigated in the context of infectious disease and considered a threat to the developing fetus. However, recently the paradigm of a sterile fetal life has been challenged and it seems that there is a naturally occurring microbiome colonizing the healthy placenta. Our understanding of the role of the indigenous microbiota in human reproduction is in its infancy. Nonetheless, there is a growing body of literature supporting the relevance of placental microbes in the establishment of immune tolerance. According to a study by Aagaard et al. (2014), the placenta microbiome is composed of nonpathogenic commensal bacteria and particularly members of the Firmicutes, Tenericutes, Proteobacteria, Bacteroidetes, and Fusobacteria phyla. Based on comparison to data from non-pregnant individuals, the placental bacterial microbial profile is reportedly most similar to the oral microbiome.
By the end of year 2015, 13 studies have to our knowledge been published regarding human papillomavirus (HPV) infection in the placenta. Eleven of the studies (n=35-339) report the prevalence of HPV DNA in the placenta to be 3-75%. HPV DNA has also been detected in placenta samples obtained transabdominally or by cesarean sections, which reduces the likelihood of contamination from the birth canal. HPV DNA has been localized in syncytiotrophoblasts and trophoblasts have been suggested to be the preferential target for HPV. In a cell culture model, HPV16 has been shown to carry out its complete life cycle in trophoblasts and its early proteins reportedly modify trophoblast growth. HPV infection has been suggested to elicit adverse effects on pregnancy. In line with this notion, HPV16 induced abnormal placental growth resulting pregnancy wastage in mouse embryos.
The composition and interactions of the viral, bacterial and fungal microbiome in the placenta as well as its role in health and disease will be discussed in this lecture.
Aagaard K, Ma J, Antony KM, Ganu R, Petrosino J, Versalovic J. The placenta harbors a unique microbiome. Sci Transl Med 2014;6(237):237ras65