Ag-dependent Engagement of CD8+ T Cells with H-2Kb on Brain Endothelium Required for CD8+ T Cell entry and Cerebral Manifestation of Malaria

Abstract

Abstract Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection with high mortality. The immune system is a key participant as the cerebral manifestation is heavily reliant on CD8+ T cell infiltration and neuroinflammation. In this disease etiology, elevated blood cytokine levels lead to increased adhesion and antigen (Ag)-presenting molecules on brain endothelium prior to CD8+ T cell entry and onset of neurological symptoms. Using the animal model of experimental cerebral malaria (ECM) we sought to further define these interactions in vivo at the blood-brain barrier. While direct interaction with MHC class I on cerebrovascular endothelial cells (CECs) has been put forward as a putative mechanism for ECM, it has not been directly confirmed in vivo. We therefore hypothesized that Ag presentation by discrete MHC class I molecules on CECs would be required for CD8+ T cells to enter the brain and establish ECM. To test this, we crossed CDH5-Cre mice with novel H-2Kb LoxP and H-2Db LoxP mice to create endothelium-specific, individual class I cKO mice. In CDH5-Cre H-2Kb mice, we show that with T cell development fully intact, CD8+ T cell infiltration into brain is decreased in frequency and number at baseline and during the infection. T cells that do enter are increasingly naive with effector responses attenuated. Importantly, mice with loss of H-2Kb on CECs show extended survival and protection from cerebral complications; as assessed by 2-photon imaging, small-animal MRI and immunofluorescence. Together, these data demonstrate that parasite-specific CD8+ T cells must undergo Ag-dependent engagement with H-2Kb class I molecule on CECs in order to fully activate CD8+ T cells to enter brain parenchyma and mediate ECM development.