Microfluidic Modeling of Cell−Cell Interactions in Malaria Pathogenesis

Abstract

The clinical outcomes of human infections by Plasmodium falciparum remain highly unpredictable. A complete understanding of the complex interactions between host cells and the parasite will require in vitro experimental models that simultaneously capture diverse host–parasite interactions relevant to pathogenesis. Here we show that advanced microfluidic devices concurrently model (a) adhesion of infected red blood cells to host cell ligands, (b) rheological responses to changing dimensions of capillaries with shapes and sizes similar to small blood vessels, and (c) phagocytosis of infected erythrocytes by macrophages. All of this is accomplished under physiologically relevant flow conditions for up to 20 h. Using select examples, we demonstrate how this enabling technology can be applied in novel, integrated ways to dissect interactions between host cell ligands and parasitized erythrocytes in synthetic capillaries. The devices are cheap and portable and require small sample volumes; thus, they have the potential to be widely used in research laboratories and at field sites with access to fresh patient samples. With over 500 million clinical cases and 1 million deaths per year, malaria presents a devastating global health problem. Samples from patients with severe disease suggest that binding of malaria-infected red blood cells (iRBCs) to host mammalian cells plays an important role in precipitating blood vessel blockages that can cause organ failure. Yet, some individuals in endemic countries harbor parasites without significant clinical symptoms. To help explore variations in disease outcomes, we developed microfluidic channels that mimic many potential features of severe disease. Synthetic microfluidic channels, with sizes and shapes resembling small capillary networks, were coated with pure host proteins or cultured mammalian cells expressing host ligands. We could therefore simulate binding of iRBCs under high-pressure fluid flow in a realistic capillary environment. By tracking the fate of individual iRBCs, we observed parasite-to-parasite variation in adhesion and an unexpected drop in adhesion when iRBCs passed through the thinnest capillaries. We also showed engulfment of iRBCs by phagocytic cells under fluid flow. The microfluidic devices should serve as powerful field tools for understanding severe malaria because the system is easy to use, requires very small sample volumes, and is portable for on-site analysis of patient samples in the field.