In this study, the acute (1-3 days after onset) serum and CSF specimens of patients with a clinical diagnosis of JE but negative for JEV-specific IgM antibody testing were obtained for diagnosis purposes from JE surveillance laboratories in Yunnan (250 cases), Guizhou (120 cases) and Gansu (50 cases) provinces of China in 2006 and 2008. Here, CD40LG is linked to Japanese encephalitis.