A previous study suggested that pleural effusion caused by MP infection can be classified into two patterns: one characterized by no detection of the MP genome and lower levels of cytokines, including interleukin 18 and interleukin 8, and the other, characterized by persistent chest disease with detection of the MP genome and higher levels of interleukin 18 and interleukin 8 [22]. The gene discussed is CXCL8; the disease is Pleural effusion.