CD40LG and viral infectious disease: Seroprevalence for IgM and IgG in 355 individuals with suspected syndromes was significantly higher than those of 1295 asymptomatic participants (IgM and IgG seropositivities were 3.38% vs. 1.70% and 7.89% vs. 5.17%, respectively), indicating that viral infection in some cases has mild or even no clinical manifestations.