CD40LG and infection: For serology, we also used a twofold increase in ELISA IgM/IgG titers as the criteria for acute influenza infection instead of the fourfold increase in traditional titer21 assays that would increase the sensitivity at the expense of some false positives. However, it has been reported that increase in antibodies’ titers after infection ranges from 1.2‐ to 10.2‐fold and 39%–55% of infected persons would not have a fourfold or greater rise in antibody titer after infection.42