To better understand the nature of MAS/HPS induced by A. phagocytophilum infection, we studied in vivo and in vitro responses of NK, NKT, and CD8 T lymphocytes from infected animals to determine if their interactions with A. phagocytophilum-loaded APCs results in delivery of cytotoxic cargo dissociated from intracellular production of IFNγ. Here, IFNG is linked to Hermansky-Pudlak syndrome.