The MIF and most EIAs detect antibody response against proteins on the surface of Chlamydiae, and established guidelines on the diagnostic criteria for acute C. pneumoniae infections are available: IgM appears in the first infection in 3 weeks, IgG in 6–8 weeks, and if adequately timed paired sera are available, a ≥4-fold IgG titer rise can be seen upon infection and reinfection (Wang and Grayston, 1986). This evidence concerns the gene CD40LG and infection.