From the viewpoint of the immune response to M. pneumoniae, despite high seropositivity (57.8%) (Table 1) and seroconversion rates of M. pneumoniae IgM (50.6%) (Table 2) in acute Q fever, a high IgG seropositivity rate during the acute phase (50.5%), a low IgG seroconversion rate (23.6%), and various concordant rates between the 2 ELISA kits (Table 4) are not typical serological patterns of acute M. pneumoniae infection. The gene discussed is CD40LG; the disease is Q fever.