Development of an enzyme immunoassay for the serodiagnostic of tuberculosis and mycobacterioses

An enzyme-linked immunosorbent assay (ELISA) test has been developed for the serodiagnosis of mycobacterioses. The test is based on an interspecific antigen, antigen 60 (A60). This antigen belongs to the group of thermostable macromolecular antigens and is the principal constituent of tuberculin RT 23. A60 is composed of proteins, polysaccharides and lipids in a ratio that varies with the growth cycle of the mycobacterium. The test detects antibodies against mycobacteria and is most effective in cases of active infections. We found that the best way to cope with the day-to-day variations in the results obtained was to transform the absorbance values into arbitrary IgG units. The variations observed with IgM antisera were, however, too great to allow more than a qualitative test. Healthy individuals are negative in the IgG and IgM tests and tuberculous patients are usually positive in the IgG test. The presence of IgM antibodies was only rarely observed. For IgG antibodies, the best discriminative power at a 1:100 dilution of the analyzed sera seemed to lie at 125 sero-units. It was found that some sera originating from clinically documented tuberculous cases responded in a poor way in this test.