Real-Time Imaging Reveals the Dynamics of Leukocyte Behaviour during Experimental Cerebral Malaria Pathogenesis

Abstract

During experimental cerebral malaria (ECM) mice develop a lethal neuropathological syndrome associated with microcirculatory dysfunction and intravascular leukocyte sequestration. The precise spatio-temporal context in which the intravascular immune response unfolds is incompletely understood. We developed a 2-photon intravital microscopy (2P-IVM)-based brain-imaging model to monitor the real-time behaviour of leukocytes directly within the brain vasculature during ECM. Ly6Chi monocytes, but not neutrophils, started to accumulate in the blood vessels of Plasmodium berghei ANKA (PbA)-infected MacGreen mice, in which myeloid cells express GFP, one to two days prior to the onset of the neurological signs (NS). A decrease in the rolling speed of monocytes, a measure of endothelial cell activation, was associated with progressive worsening of clinical symptoms. Adoptive transfer experiments with defined immune cell subsets in recombinase activating gene (RAG)-1-deficient mice showed that these changes were mediated by Plasmodium-specific CD8+ T lymphocytes. A critical number of CD8+ T effectors was required to induce disease and monocyte adherence to the vasculature. Depletion of monocytes at the onset of disease symptoms resulted in decreased lymphocyte accumulation, suggesting reciprocal effects of monocytes and T cells on their recruitment within the brain. Together, our studies define the real-time kinetics of leukocyte behaviour in the central nervous system during ECM, and reveal a significant role for Plasmodium-specific CD8+ T lymphocytes in regulating vascular pathology in this disease.

Monocyte- and Neutrophil-Derived CXCL10 Impairs Efficient Control of Blood-Stage Malaria Infection and Promotes Severe Disease

“…(35)(36)(37)(38)(39). Moreover, recent studies revealed a role for inflammatory monocytes, in the recruitment of CD8 + T cells to the brain of P. berghei ANKA-infected mice (40).…”

IRGM3 Contributes to Immunopathology and Is Required for Differentiation of Antigen-Specific Effector CD8+T Cells in Experimental Cerebral Malaria

“…However, the effect was modest (ϳ2-to 3-fold) for all parameters. Decreases in T cell recruitment of similar magnitude, resulting from depletion of inflammatory monocytes, do not result in protection from ECM (58). Therefore, it seems unlikely that the observed diminution in the absolute number of recruited CD8 ϩ T cells could account for the dramatically divergent clinical outcomes.…”

“…PbA-infected Irgm3 Ϫ/Ϫ mice had reduced CCL2 protein as well as decreased monocyte sequestration in the brain. The presence of monocytes is obvious in ECM brain lesions, and they have been shown to enhance recruitment of CD8 ϩ T cells to the brain during ECM, probably via production of T cell-attracting chemokines (58). However, inflammatory monocytes are nonessential for the development of ECM pathogenesis (58,59).…”

“…The presence of monocytes is obvious in ECM brain lesions, and they have been shown to enhance recruitment of CD8 ϩ T cells to the brain during ECM, probably via production of T cell-attracting chemokines (58). However, inflammatory monocytes are nonessential for the development of ECM pathogenesis (58,59). Therefore, although Irgm3 deficiency may contribute to the decreased numbers of CD8 ϩ T cells found in the brains of infected mice through decreased recruitment of inflammatory chemokine-producing monocytes, it is unlikely that this pathway ultimately is responsible for protection from ECM.…”

Platelet-mediated adhesion facilitates leukocyte sequestration in hypoxia-reoxygenated microvessels

“…In some conditions or diseases, for example, multiple sclerosis, most leukocytes transmigrate through the endothelial barrier and infiltrate into the adjacent tissues, causing lesions in the affected area (Compston and Coles, 2008). On the contrary, as in cerebral malaria, a few leukocytes transmigrate through the endothelium, but most are sequestrated within the microvessels, thus inducing local ischemia (Coltel et al, 2004;Pai et al, 2014). Yet, the reasons leading to leukocyte transmigration or sequestration in different conditions are poorly understood.…”