Detection by ELISA of specific IgG to mycobacterial antigen 60 in a tuberculous exudate

A case of active multicavitary tuberculosis is reported. In the 3rd month of treatment, an X-ray film of the thorax showed right pleural effusion. The properties of the pleural fluid were those of an exudate with high adenosine deaminase activity. An ELISA was performed to detect specific IgG antibody to mycobacterial antigen 60 in serum before the treatment and on a two-monthly basis following the initiation of therapy until completion of the course. Values were all above 1,750 U. Moreover, an ELISA test using the same antigen was done on pleural fluid, and a high IgG titer was obtained (950 U). A cutoff for a positive ELISA test was established at 240 U in serum and 150 U in other biologic fluids.