As for the correlation between the serum CMV IgM and EBV VCA IgM antibody titers in children with primary EBV infection manifesting as infectious mononucleosis, serum CMV IgM titers showed a significant correlation with serum EBV VCA IgM titers (r = 0.245, P = .003). This evidence concerns the gene CD40LG and infectious mononucleosis.