Aims:
Malaria in pregnancy (MiP) is a serious health and economic burden. Antibodies can clear placental infection, and key interactions between VAR2CSA on infected erythrocytes, IgG subclasses and phagocytic cells occur via a process termed as opsonic phagocytosis. The aims of my project are to characterize functional activities of different monocyte cell models using opsonic phagocytosis assays and measure IgG subclass responses to three different DBL domains.
Methods:
Monocyte cell models, namely, THP-1, Monomac6 and donor monocytes were assessed for their surface receptor (FcγR) activity by conducting phenotyping and receptor blocking followed by opsonic phagocytosis using CS2 parasite line. Additionally, ELISA was conducted to measure IgG1-4 subclass responses against DBL1, DBL3 and DBL5 domains on 573 plasma samples from Malawian pregnant women receiving intermittent preventive treatment in pregnancy (IPTp). Statistical analyses were then carried out on correlating antibody responses with clinical outcomes.
Results:
Different combinations of FcγR(s) carry out opsonic phagocytosis in different cell models. Monomac6 cells showed poor opsonic uptake as compared to THP-1 cells. Phenotypically, both these cell lines lack FcγRIII expression on their surface. ELISA assays suggest that maternal factors like gravidity, age and microscopic infection at study enrolment are positively correlated with high antibody levels at enrolment. Out of all IgG subclasses, IgG1 and IgG2 showed strongest associations while IgG3 the weakest. Clinical outcomes at delivery, especially placental malaria, are strongly associated with IgG1 levels at enrolment, and weakly with IgG3 and IgG4. Since IgG2 and IgG4 are not crucial for opsonic phagocytosis as per the literature, the antibody levels measured in this study are representative as markers of exposure, rather than being protective.
Conclusions:
Different receptors on phagocytic cells propel opsonic phagocytosis during MiP. High antibody levels during pregnancy are greatly correlated with maternal factors like gravidity, age and microscopic infection.