CD40LG and infection: Effects of infection and its interaction with housing on changes in antibody titers after infection After infection with PRRSV on day 44, changes of KLH-IgM (delta 46–44, 48–44, and 52–44) were not only affected by delta-day (F(2.99) = 75.6, P < 0.001), but also by the interaction between infection and delta-day (F(2.99) = 3.4, P < 0.05).