Investigation of antibody-mediated immune mechanisms during submicroscopic infections of pregnancy-associated malaria in pregnant women from Colombia

• Author / Creator

  Wiebe, Madeleine

• Malaria has been a threat to humans for centuries and continues to be a global health problem. Repeated exposure to malaria in childhood can result in protective immunity that reduces parasite invasion of red blood cells and the sequestration of infected red blood cells (iRBC) in the tissues. However, pregnancy offers a new site of attack for the parasite, the placenta. In the placenta, iRBCs bind to chondroitin sulfate A (CSA) and sequester here via variable surface antigens (VSAs) that are only expressed during pregnancy. One known VSA is VAR2CSA, a large 350 kD protein. In high transmission areas of sub-Saharan Africa, multiple instances of pregnancy-associated malaria (PAM) can result in acquired antibodies that block iRBC binding to CSA. Thus, these antibodies may be protective against adverse birth outcomes, which include low birthweight, preterm birth, and maternal anemia.
  Previously, we conducted a longitudinal study in Colombia, where both Plasmodium falciparum and P. vivax co-circulate, which followed pregnant women from early pregnancy to delivery. This included a cohort of women who had at least one submicroscopic infection of PAM during pregnancy, which cannot be detected with microscopy diagnostic methods but were instead detected retrospectively with qPCR. In this subset of infected women, we observed a protective association between antibody inhibition against iRBC binding to CSA in vitro and maternal hemoglobin at delivery, but the mechanisms behind this association are unknown. To develop effective treatments against PAM, the human host’s own defense mechanisms must be well understood. In this thesis, we aimed to elucidate potential protective mechanisms of the humoral immune system against adverse pregnancy outcomes, with a focus on protection from maternal anemia. We first assessed IgG and IgM-VAR2CSA levels against recombinant VAR2CSA and found variable levels within the cohort, but these levels were not associated with improved pregnancy outcomes. We also assessed total VSAPAM IgG by testing for antibody staining in flow cytometry against whole iRBCs selected to express VSA(s) that adhere to CSA, but we observed minimal activity in this assay. But, as we previously observed functional activity in this cohort, we then turned to other measurements of antibody-mediated functional activity.
  Cytophilic antibodies acquired during PAM may mediate classical complement activation through fixation of the first component, C1q, and recruit phagocytes through opsonic phagocytosis. We observed functional activity in sera collected from the SMI cohort in both assays, and both were negatively associated with infant birthweight. This may indicate a dysregulated immune response which could contribute to placental pathology, but further investigation is required. Additionally, IgM-VAR2CSA and C1q fixation levels were highly associated to each other in early pregnancy and at delivery, which suggests IgM may fix C1q to a greater extent than IgG antibodies. No further associations between the humoral response and maternal anemia were observed, which may be due to several factors including study setting, cohort size, and the assays used for measurements of humoral immunity. Further investigation should focus on understanding the connections between humoral immunity and adverse pregnancy outcomes and elucidating mechanisms such that protective responses can be elicited in future therapies and vaccines against PAM.

• Subjects / Keywords

  • Pregnancy-associated malaria
  • Maternal anemia
  • Complement
  • Opsonic phagocytosis
  • Submicroscopic infection
  • Malaria
  • Pregnancy

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-m6w9-9852

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.