MMP9 and tick-borne encephalitis: Acute-phase TBE patients have shown elevated MMP-9 in the serum and CSF [54,55], whilst patients with WNV infection exhibited elevated serum/plasma levels of a number of inflammatory cytokines [56,57] including IL-1β, TNF-α and IFN-γ [57] and MMP-9 [43] all of which have been shown to compromise the BBB [38,43,58,59,60].