IL18 and tick-borne encephalitis: While not much is known about the role of NK cells in TBE prior to the development of CNS disease, NK cell-associated cytokines, including IL-12, IL-15, IL-18, IFN-γ, and TNF-α are upregulated in the serum of patients during severe disease (56) and NK cells can further be detected in the CSF; indicating their migration to the CNS (57).