CD40LG and tick-borne encephalitis: Although the assessment of anti-TBEV immunoglobulin G (IgG) in either blood or CSF during the second phase of the disease is the basis of routine diagnosis of TBE, there are some limitations that may cause diagnostic problems, like persistent immunoglobulin M (IgM) antibodies in serum, and cross-reactivity of the antibodies [5,7,8,10,11,12,13,14].