Human Microglia Respond to Malaria-Induced Extracellular Vesicles

Abstract

Microglia are the chief immune cells of the brain and have been reported to be activated in severe malaria. Their activation may drive towards neuroinflammation in cerebral malaria. Malaria-infected red blood cell derived-extracellular vesicles (MiREVs) are produced during the blood stage of malaria infection. They mediate intercellular communication and immune regulation, among other functions. During cerebral malaria, the breakdown of the blood–brain barrier can promote the migration of substances such as MiREVs from the periphery into the brain, targeting cells such as microglia. Microglia and extracellular vesicle interactions in different pathological conditions have been reported to induce neuroinflammation. Unlike in astrocytes, microglia–extracellular vesicle interaction has not yet been described in malaria infection. Therefore, in this study, we aimed to investigate the uptake of MiREVs by human microglia cells and their cytokine response. Human blood monocyte-derived microglia (MoMi) were generated from buffy coats of anonymous healthy donors using Ficoll-Paque density gradient centrifugation. The MiREVs were isolated from the Plasmodium falciparum cultures. They were purified by ultracentrifugation and labeled with PKH67 green fluorescent dye. The internalization of MiREVs by MoMi was observed after 4 h of co-incubation on coverslips placed in a 24-well plate at 37 °C using confocal microscopy. Cytokine-gene expression was investigated using rt-qPCR, following the stimulation of the MoMi cells with supernatants from the parasite cultures at 2, 4, and 24 h, respectively. MiREVs were internalized by the microglia and accumulated in the perinuclear region. MiREVs-treated cells increased gene expression of the inflammatory cytokine TNFα and reduced gene expression of the immune suppressive IL-10. Overall, the results indicate that MiREVs may act on microglia, which would contribute to enhanced inflammation in cerebral malaria.

A Profound Membrane Reorganization Defines Susceptibility of Plasmodium falciparum Infected Red Blood Cells to Lysis by Granulysin and Perforin

“…All symptoms of clinical malaria and in particular its most severe complication, cerebral malaria, are caused by the exponential growth of the parasite during the blood stage, subsequent cytoadherence and sequestration of iRBCs at critical sites in the microvasculature as well as overreactivity of the proinflammatory immune response (51)(52)(53). Therefore, to prevent malaria-associated morbidity and mortality tight control of parasitemia is essential.…”

Factors influencing phagocytosis of malaria parasites: the story so far

“…In a recent study, CD14 + monocytes were identified as the main producers of CXCL-10 when challenged with P. falciparum , but the sub-sets that were involved and the association between CXCL-10 levels and parasite burden in humans remain unknown [ 69 ]. In addition, using an in vitro model of human blood monocyte-derived microglia cells, the uptake of IE-derived extracellular vesicles was shown to cause down-regulation of IL-6 and IL-10 gene expression [ 70 ]. When mouse macrophages were challenged with these vesicles, they produced TNF and up-regulated their CD40 expression [ 71 ].…”

Neurovascular Interactions in Malaria

“…After the rupture of the BBB, pRBC, EV-pRBC, and molecules such as heme [102] and hemozoin can invade the brain parenchyma and be recognized by microglia [84,103,104]. In ECM, a rapid response of microglial cells occurs with morphological alteration characteristic of microglial activation [90,105,106].…”