CD8+ T Cells Induce Fatal Brainstem Pathology during Cerebral Malaria via Luminal Antigen-Specific Engagement of Brain Vasculature

Abstract

Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection that results in thousands of deaths each year, mostly in African children. The in vivo mechanisms underlying this fatal condition are not entirely understood. Using the animal model of experimental cerebral malaria (ECM), we sought mechanistic insights into the pathogenesis of CM. Fatal disease was associated with alterations in tight junction proteins, vascular breakdown in the meninges / parenchyma, edema, and ultimately neuronal cell death in the brainstem, which is consistent with cerebral herniation as a cause of death. At the peak of ECM, we revealed using intravital two-photon microscopy that myelomonocytic cells and parasite-specific CD8+ T cells associated primarily with the luminal surface of CNS blood vessels. Myelomonocytic cells participated in the removal of parasitized red blood cells (pRBCs) from cerebral blood vessels, but were not required for the disease. Interestingly, the majority of disease-inducing parasite-specific CD8+ T cells interacted with the lumen of brain vascular endothelial cells (ECs), where they were observed surveying, dividing, and arresting in a cognate peptide-MHC I dependent manner. These activities were critically dependent on IFN-γ, which was responsible for activating cerebrovascular ECs to upregulate adhesion and antigen-presenting molecules. Importantly, parasite-specific CD8+ T cell interactions with cerebral vessels were impaired in chimeric mice rendered unable to present EC antigens on MHC I, and these mice were in turn resistant to fatal brainstem pathology. Moreover, anti-adhesion molecule (LFA-1 / VLA-4) therapy prevented fatal disease by rapidly displacing luminal CD8+ T cells from cerebrovascular ECs without affecting extravascular T cells. These in vivo data demonstrate that parasite-specific CD8+ T cell-induced fatal vascular breakdown and subsequent neuronal death during ECM is associated with luminal, antigen-dependent interactions with cerebrovasculature.

Perforin Expression by CD8 T Cells Is Sufficient To Cause Fatal Brain Edema during Experimental Cerebral Malaria

“…This indicates that disruption of the BBB within the brainstem could induce the observed symptoms. These results complement recent work by Swanson et al showing that ECM induces neuronal death (30). These results indicate that the extensive vascular leakage within the brainstem results in the death of critical neurons.…”

“…This study demonstrates that disruption in the organization of tight junctions has significant global consequences that can lead to organ-wide pathology. Recent work has identified a reduction in claudin-5 during ECM (30). Here, we confirm a significant reduction in claudin-5 and also show that this phenomenon is shared by the tight-junction protein occludin.…”

Interferon regulatory factor 1 is essential for pathogenic CD8+ T cell migration and retention in the brain during experimental cerebral malaria

“…Adhesion molecules LFA‐1 and very late antigen‐4 are expressed by pathogenic CD8+ T cells during ECM, and these molecules interact with ICAM‐1 and VCAM‐1 on the surface of activated brain endothelial cells, respectively. These interactions facilitate the retention of effector CD8+ T cells in the brain intravascularly, leading to brain vascular leakage and ECM death (Swanson II et al, ). Because IFNγ stimulates activation of brain endothelial cells (Howland, Poh, et al, ; Weiser, Miu, Ball, & Hunt, ) and IRF1KO mice produced less IFNγ, we hypothesised that endothelial cells may be partially activated and expressed less ICAM‐1 and VCAM‐1.…”

“…Endothelial activation is a feature of ECM pathogenesis with expression of adhesion molecules being responsible for sequestration of leucocytes (Swanson et al, ). Here, IRF1KO mice exhibited less leucocyte sequestration in the brain due to downregulated ICAM‐1 and VCAM‐1 expressions on the brain endothelial cells (Figure a and b).…”

“…Direct effect of IRF1 on VCAM‐1 expression has been previously reported (Lechleitner, Gille, Johnson, & Petzelbauer, ; Neish et al, ; Sun et al, ), whereas ICAM‐1 expression is shown to be independent of IRF1 activity (Sun et al, ). Expression of ICAM‐1 and VCAM‐1 during ECM is induced primarily by IFNγ (Amani et al, ; Bauer et al, ; Swanson et al, ). We observed that the level of circulating IFNγ was reduced, and thus, it was logical that ICAM‐1 and VCAM‐1 expressions were affected by the lower level of IFNγ in IRF1KO mice.…”