CD40LG and infection: Since the measurement of anti-VCA IgG response generally has an equivalent value of detecting a past infection as anti-EBNA-1 IgG response and some individuals might either be anti-VCA IgM nonresponders or have lost anti-EBNA response years after acute primary infection, we choose to detect anti-VCA IgG response in sera in the study and this has also been applied in other EBV seroepidemiological studies [7, 16, 18, 20, 43].