Evaluation of complex and defined antigens of Mycobacterium tuberculosis in an IgG-specific ELISA for the diagnosis of tuberculosis

In recent years, several defined antigens of Mycobacterium tuberculosis have become available either by purifying the natural antigens using biochemical procedures, or by producing large quantities of recombinant antigens, using recombinant DNA technology. In this study, we evaluated these defined antigens of M. tuberculosis, along with the complex antigens, for humoral immune responses in an IgG-specific enzyme-linked immunosorbent assay (ELISA). We hoped to develop a tuberculosis-specific ELISA of diagnostic potential. Our results show that IgG antibodies to the complex antigens (i.e. culture filtrate, cell wall and sonicate) and to some of the defined antigens (i.e. 38-kD antigen and lipoarabinomannan) of M. tuberculosis were significantly elevated in the sera of tuberculous patients, as compared to healthy contacts of tuberculous patients and patients suffering from nonmycobacterial infections. Among the IgG subclasses, IgG2 antibody reactive with culture filtrate, cell wall, and lipoarabinomannan antigens was elevated in the sera of most tuberculous patients. Since the complex antigens are difficult to standardize, and batch-to-batch variations may occur with respect to the amount of active components in different batches, the use of defined antigens of M. tuberculosis in ELISA may be a better alternative in the early and specific diagnosis of tuberculosis.