In a suspected case of acute M pneumoniae infection-induced pleural effusion, if lymphocytes are the dominant cell fraction and the ADA level is high in the pleural effusion, it is important to perform an interferon-gamma release assay and polymerase chain reaction test for M tuberculosis to investigate the possibility of tuberculous pleurisy while waiting for the acid-fast bacterial culture results. This evidence concerns the gene IFNG and pleural tuberculosis.