Hypoxia promotes cytolytic activity of CD8 T cells and pathogenesis in cutaneous leishmaniasis

Abstract

Abstract Leishmaniasis is a disease caused by protozoan parasites of the genus Leishmania and the most common form of the disease is cutaneous leishmaniasis (CL). A fundamental question in CL is what regulates the development of severe disease, which is critical to develop therapies to ameliorate pathology. In a series of studies, we demonstrated CD8 T cell-dependent cytotoxicity as the main inducer of immunopathology in CL. This result was unexpected since IFN-γ production by CD8 T cells plays a protective role by promoting pathogen elimination. To resolve this paradox, we studied the CD8 T cells in different anatomic sites and found that the effector function of CD8 T cells in CL depends on their location: while CD8 T cells are cytotoxic (GzmB+) and produce little IFN-γ in the skin lesions, CD8 T cells in the draining lymph nodes (dLN) have the opposite profile. Importantly, GzmB-CD8 T cells from dLN quickly upregulate GzmB after injection into CL lesions. By transcriptional profiling, we found that CD8 T cells in lesions but not dLN have a hypoxic signature. In vivo, we observed that CL lesions are hypoxic using the Oxyphor G4 oxygen probe and pimonidazole staining. In vitro, we found that induction of hypoxia was sufficient to convert GzmB- into GzmB+ CD8 T cells, and significantly decreased CD8 T cell production of IFN-γ. In vivo, blocking hypoxia-inducible factor (HIF), a master regulator of hypoxia, with acriflavine decreased lesion development in mice. Mice with CD8 T cell deficient in HIF-1α produced significantly less GzmB in the skin lesions compared to wildtype mice. Together, our results suggest that the hypoxic signaling through the transcription factor HIF in CL lesions is necessary to convert CD8 T cells into pathogenic CD8 T cells in the skin lesion. Supported by grants from NIH (1R01AI162711)