IgG subclass antibody response to mycobacterial serine protease at different stages of pulmonary tuberculosis

Tuberculosis (TB) is a chronic bacterial infection caused by M. Tuberculosis. Studies of antibody response in TB have focussed mainly on their usefulness as a diagnostic serological tool, with little attention given to analysis of antibodies at the isotype and subclass level in relation to disease pathogenesis. Hence the present study was done to analyse IgG subclass response at different stages of tuberculosis, in order to understand the immunological events associated with disease development.

Sera samples were collected from 104 subjects: 79 tuberculosis patients (fresh, relapse and chronic cases) and 25 healthy normals. IgG subclass antibody response was analysed by indirect plate peroxidase ELISA against previously reported mycobacterial serine protease (ES-31) antigen.

Fresh cases of tuberculosis showed increased IgG1 and IgG3 antibodies, while a few cases showed moderately increased IgG2. IgG1 and IgG3 were found to be elevated with increased bacillary load. Relapse and chronic cases showed increased IgG1 and IgG3, while positivity to IgG2 was decreased. Chronic cases showed a moderate increase in IgG4 antibody. Thus IgG1 and IgG3 were predominant in all forms of tuberculosis.

The elevated levels of IgG1 and IgG3 antibodies to mycobacterial serine protease in active tuberculosis observed in this study provide an additional marker for diagnosis of tuberculosis. Furthermore, the higher level of these antibodies with high bacillary load patients and in chronic cases of tuberculosis may provide valuable insight into their possible role in disease progression.