The route of infection might play a crucial role, since genital experimental C. suis S45 infections in sows led to an evident seroconversion, detected by an ELISA using purified S45 elementary bodies (EBs) as the antigen [36]: C. suis S45-specific serum IgM and IgG were observed from seven days post-primary infection onwards, and the mean titres peaked at 14 or 21 days post-infection. Here, CD40LG is linked to infection.