Lucchi, Naomi Wangui
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Pregnant women, especially those in their first pregnancy, appear to be more susceptible to malaria infections even in endemic areas where by adulthood substantial acquired immunity to malaria is apparent. This often results in what is referred to as placental malaria (PM). PM is a major public health problem associated with poor fetal outcomes such low birth weight and maternal anemia. It is characterized by the sequestration of malarial-infected red blood cells (iRBCs) in the placental intervillous spaces and infiltration of maternal immune cells. While the accumulation of iRBCs is known to be mediated by the binding of iRBCs to syncytiotrophoblast (ST), fetal cells in direct contact with maternal blood, little is known about how this binding influences ST immune function. This has been due in part to the lack of an appropriate system to perform the necessary experiments. In this study, such a system was developed using both primary trophoblasts cells and a placental choriocarcinoma cell line, BeWo. This system was used to assess the biochemical and immunological changes induced in ST upon specific binding of ST-adherent iRBCs and malarial components such as hemozoin (the malaria pigment) and crude malaria antigen. For comparison, ST responses to ST lipopolysaccharide (LPS) were assessed. The binding of iRBC led to an increase in the tyrosine phosphorylation of at least two ST proteins. The mitogen activated protein kinase (MAPK), JNK pathway, involved in many cellular activation processes and gene expression of most immune factors, was also activated. Stimulation with LPS, malarial antigens and hemozoin all led to an increased phosphorylation of ERK1/2 MAPKs. Stimulation of the ST cells with LPS led to increases in the gene expression and protein secretion of TNF-±, MIP-1± and MIP-1² and IL-8. Only modest increases in expression of TNF-±, TGF-² and IL-8 mRNA were observed with iRBC binding and this did not result in the secretion of these cytokines. However, binding of iRBC led to the secretion of macrophage migration inhibitory factor (MIF) and to the chemotaxis of peripheral blood mononuclear cells. Treatment with hemozoin stimulated the secretion of IL-8. Taken together, these results suggest that during PM, the binding of iRBCs and interaction with malarial components stimulates intracellular signaling and gene expression changes in the ST. This leads to the secretion of proinflammatory chemokines that influence the local immunological milieu, making the ST an active immunologic player in the placental environment during PM.