Critical roles of NK and CD8⁺ T cells in central nervous system listeriosis

Listeria monocytogenes (LM) causes a life-threatening infectious disease affecting the brain of humans and domestic animals. Unfortunately, no adequate murine models for CNS listeriosis exist. Using intraparenchymal injection, we have established a new murine model for CNS listeriosis. Injection of a small volume of bacterial suspension limits the bacteria to the brain parenchyma with no leakage into the ventricular system. This new method enabled us to investigate the progression of and recovery from listerial brain infection, revealing roles for both innate and adaptive immune cells in CNS listeriosis. In the early phase of CNS listeriosis, NK cell-derived IFN-γ is a critical cytokine in the limitation of bacterial growth by the host defense. During the later phase, CD8⁺ but not CD4⁺ T cells play a critical role and LM-specific CD8⁺ T cells kill LM-infected microglia. Thus, innate and adaptive immune responses combine to successfully eliminate bacteria from the brain.