CD40LG and tick-borne encephalitis: In contrast to unvaccinated TBE patients who initially develop high serum levels of IgM antibodies that are followed by low specific IgG at the beginning of neurologic involvement, neurological symptoms in VBT patients are accompanied by markedly elevated levels of specific and neutralizing IgG antibodies with high avidity to TBEV and by the absence or low levels of IgM antibodies indicating an anamnestic immune response (Stiasny et al., 2009; Lotric-Furlan et al., 2017).