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Scholarly Works (8 results)

  • Thesis
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UC San Francisco Electronic Theses and Dissertations (2011)

Placental infections can lead to severe pregnancy complications as well as infection of the fetus with significant morbidity and mortality. Among pathogens that can cross the maternal-fetal barrier is the facultative intracellular bacterium, Listeria monocytogenes, which is highly amenable to experimental analysis. We used this model pathogen to study infection dynamics at the maternal-fetal interface.

Using human placental organ cultures, we found that the syncytiotrophoblast -- which constitutes most of the placental surface and is bathed in maternal blood in vivo -- is highly resistant to L. monocytogenes infection. We hypothesize this resistance to be a result of the unique biophysical characteristics of the syncytium. We present our preliminary data in support of this hypothesis and the development of the mouse trophoblast model system that will be used to study this further.

We next show that extravillous cytotrophoblasts (EVT) -- which anchor the placenta in the decidua (uterine lining) -- serve as the primary portal of entry for pathogens into the placenta. However, they restrict bacterial growth and represent another barrier to infection. Using primary human trophoblast cell culture, we characterized the intracellular fate of L. monocytogenes in EVT. We found that these cells entrap bacteria in vacuolar compartments where they are degraded. Specifically, bacteria remain confined to acidified vacuoles and co-localize with LAMP1, consistent with bacterial degradation in lysozomes. Further studies show that autophagy is not responsible for this bacteriocidal phenotype of EVT, though reactive nitrogen species and cationic microbial peptides may play a role. Efforts to further discern the bacterial killing mechanism are underway. Specifically, we are in the process of defining the global EVT transcriptional response to infection. We hope to also use these data to study the role of EVT in the development of pregnancy complications.

Our studies show that the placenta has evolved multiple mechanisms to resist pathogen infection. The syncytium is a robust barrier to invasion by blood-borne pathogens, while EVT have innate cellular defense mechanisms to restrict pathogens. Our understanding of these novel placental barriers to infection may help develop new paradigms in the diagnosis and treatment of pregnancy complications.

    Cover page: Placental Defenses Against Infection
    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2012)
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2013)
      We report a case in which placental abruption occurred at 16 weeks following first trimester diagnosis and treatment for typhoid fever. Unexpectedly Salmonella enterica serovar Typhi (S. Typhi) was found in fetal tissues at autopsy. Using information from
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2013)
        Fetal syncytiotrophoblasts form a unique fused multinuclear surface that is bathed in maternal blood, and constitutes the main interface between fetus and mother. Syncytiotrophoblasts are exposed to pathogens circulating in maternal blood, and appear to ha
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2012)
          Listeria monocytogenes causes a serious food-borne disease due to its ability to spread from the intestine to other organs, a process that is poorly understood. In this study we used 20 signature-tagged wild-type clones of L. monocytogenes in guinea pigs in combination with extensive quantitative data analysis to gain insight into extraintestinal dissemination. We show that L. monocytogenes colonized the liver in all asymptomatic animals. Spread to the liver occurred as early as 4 h after ingestion via a direct pathway from the intestine to the liver. This direct pathway contributed significantly to the bacterial load in the liver and was followed by a second wave of dissemination via the mesenteric lymph nodes (indirect pathway). Furthermore, bacteria were eliminated in the liver, whereas small intestinal villi provided a niche for bacterial replication, indicating organ-specific differences in net bacterial growth. Bacteria were shed back from intestinal villi into the small intestinal lumen and reinfected the Peyer's patches. Together, these results support a novel dissemination model where L. monocytogenes replicates in intestinal villi, is shed into the lumen, and reinfects intestinal immune cells that traffic to liver and mesenteric lymph nodes, a process that occurs even during asymptomatic colonization.
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2017)
            The bacterial pathogen Listeria monocytogenes causes foodborne systemic disease in pregnant women, which can lead to preterm labor, stillbirth, or severe neonatal disease. Colonization of the maternal decidua appears to be an initial step in the maternal component of the disease as well as bacterial transmission to the placenta and fetus. Host-pathogen interactions in the decidua during this early stage of infection remain poorly understood. Here, we assessed the dynamics of L. monocytogenes infection in primary human decidual organ cultures and in the murine decidua in vivo A high inoculum was necessary to infect both human and mouse deciduas, and the data support the existence of a barrier to initial colonization of the murine decidua. If successful, however, colonization in both species was followed by significant bacterial expansion associated with an inability of the decidua to mount appropriate innate cellular immune responses. The innate immune deficits included the failure of bacterial foci to attract macrophages and NK cells, cell types known to be important for early defenses against L. monocytogenes in the spleen, as well as a decrease in the tissue density of inflammatory Ly6Chi monocytes in vivo These results suggest that the infectivity of the decidua is not the result of an enhanced recruitment of L. monocytogenes to the gestational uterus but rather is due to compromised local innate cellular immune responses.
              Cover page: Limited Colonization Undermined by Inadequate Early Immune Responses Defines the Dynamics of Decidual Listeriosis
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2011)
              Listeria monocytogenes is a facultative intracellular bacterial pathogen that can infect the placenta, a chimeric organ made of maternal and fetal cells. Extravillous trophoblasts (EVT) are specialized fetal cells that invade the uterine implantation site, where they come into direct contact with maternal cells. We have shown previously that EVT are the preferred site of initial placental infection. In this report, we infected primary human EVT with L. monocytogenes. EVT eliminated ∼80% of intracellular bacteria over 24-hours. Bacteria were unable to escape into the cytoplasm and remained confined to vacuolar compartments that became acidified and co-localized with LAMP1, consistent with bacterial degradation in lysosomes. In human placental organ cultures bacterial vacuolar escape rates differed between specific trophoblast subpopulations. The most invasive EVT-those that would be in direct contact with maternal cells in vivo-had lower escape rates than trophoblasts that were surrounded by fetal cells and tissues. Our results suggest that EVT present a bottleneck in the spread of L. monocytogenes from mother to fetus by inhibiting vacuolar escape, and thus intracellular bacterial growth. However, if L. monocytogenes is able to spread beyond EVT it can find a more hospitable environment. Our results elucidate a novel aspect of the maternal-fetal barrier.
                Cover page: Invasive Extravillous Trophoblasts Restrict Intracellular Growth and Spread of Listeria monocytogenesCreative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2010)
                Listeria monocytogenes is an important cause of maternal-fetal infections and serves as a model organism to study these important but poorly understood events. L. monocytogenes can infect non-phagocytic cells by two means: direct invasion and cell-to-cell spread. The relative contribution of each method to placental infection is controversial, as is the anatomical site of invasion. Here, we report for the first time the use of first trimester placental organ cultures to quantitatively analyze L. monocytogenes infection of the human placenta. Contrary to previous reports, we found that the syncytiotrophoblast, which constitutes most of the placental surface and is bathed in maternal blood, was highly resistant to L. monocytogenes infection by either internalin-mediated invasion or cell-to-cell spread. Instead, extravillous cytotrophoblasts-which anchor the placenta in the decidua (uterine lining) and abundantly express E-cadherin-served as the primary portal of entry for L. monocytogenes from both extracellular and intracellular compartments. Subsequent bacterial dissemination to the villous stroma, where fetal capillaries are found, was hampered by further cellular and histological barriers. Our study suggests the placenta has evolved multiple mechanisms to resist pathogen infection, especially from maternal blood. These findings provide a novel explanation why almost all placental pathogens have intracellular life cycles: they may need maternal cells to reach the decidua and infect the placenta.
                  Cover page: Placental Syncytiotrophoblast Constitutes a Major Barrier to Vertical Transmission of Listeria monocytogenesCreative Commons 'BY' version 4.0 license
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