CD8 and CD4 T Cells Infiltrate into the Brain during ANKA Infection and Form Long-Term Resident Memory.

In the ANKA mouse model of malaria, accumulation of CD8 T cells and infected RBCs in the brain promotes the development of experimental cerebral malaria (ECM). In this study, we used malaria-specific transgenic CD4 and CD8 T cells to track evolution of T cell immunity during the acute and memory phases of ANKA infection. Using a combination of techniques, including intravital multiphoton and confocal microscopy and flow cytometric analysis, we showed that, shortly before onset of ECM, both CD4 and CD8 T cell populations exit the spleen and begin infiltrating the brain blood vessels. Although dominated by CD8 T cells, a proportion of both T cell subsets enter the brain parenchyma, where they are largely associated with blood vessels. Intravital imaging shows these cells moving freely within the brain parenchyma. Near the onset of ECM, leakage of RBCs into areas of the brain can be seen, implicating severe damage. If mice are cured before ECM onset, brain infiltration by T cells still occurs, but ECM is prevented, allowing development of long-term resident memory T cell populations within the brain. This study shows that infiltration of malaria-specific T cells into the brain parenchyma is associated with cerebral immunopathology and the formation of brain-resident memory T cells. The consequences of these resident memory populations is unclear but raises concerns about pathology upon secondary infection.