Low affinity CD8+ T cells are a critical component in the development of experimental cerebral malaria

Abstract

Abstract Malaria is responsible for at least 500 million deaths annually. Of those who become infected with malaria, around 1% develop cerebral malaria, which is fatal in 15% – 20% of patients. Therefore, understanding the immune mechanisms contributing to the lethality of cerebral malaria are critical for developing appropriate therapies. Infection with Plasmodium berghei ANKA in C57BL/6 mice induces experimental cerebral malaria (ECM), which requires activated CD8 T cells. In these experiments, we used the highly sensitive two-dimensional (2D) micropipette adhesion frequency assay to define the affinity and frequency of the immunodominant glideosome associated protein 50 (GAP50)40–48 epitope. We found both high and low affinity GAP50 specific CD8 T cells are found in the spleen (d5) and brain (d6) of ANKA infected mice. However, the 2D micropipette assay was more sensitive than tetramer staining with respective measurements of 20% vs. 1.2% of CD8 T cells in the spleen and 30% vs. 13.2% of CD8 T cells in the brain of ANKA infected mice measured as specific for GAP50. Furthermore, 67% of the antigen specific CD8 T cells in the spleen and 50% in the brain had low affinity for GAP50. These data reveal that tetramer vastly underestimates the number of antigen specific cells responding during ANKA infection. Infection with the NK65 strain of P. bergei results in similar levels of parasitemia and frequency of CD8 T cells in the brain, but ECM does not develop. Unlike ANKA infection, micropipette analysis of CD8 T cells from the brains of NK65 revealed only high affinity CD8 T cells for GAP50. These data indicate that under appreciated low affinity CD8 T cells are a vital component of the pathogenic and lethal response observed in experimental cerebral malaria.