It is well known that single serologic test has limited values for early diagnosis of MP pneumonia because of no IgM antibodies in the early stage of MP infection and long-term persistence of IgM antibodies after MP infection.1–3 In the present study, approximately one-third of patients were negative for MP-specific antibodies (33.4%, 148/418) and CAs (37.6%, 157/418) at presentation. The gene discussed is CD40LG; the disease is hyperplastic polyp.