Development of a New Indirect ELISA Method for Detection of Anti-Tuberculosis Antibodies in Human Serum

Tuberculosis is a crucial health problem. Establishing a rapid, reliable and still inexpensive diagnostic method for tuberculosis seems to be substantial in developing countries where TB has very high incidence rate. An Indirect Enzyme-linked immunosorbent Assay (ELISA) was established to detect serum antibodies against Mycobacterium tuberculosis. Three kinds of antigens were used to prepare the solid phase for antibody as­say including: purified protein derivative (PPD), M. tuberculosis Bacilli, and Mycobacterium bovis Bacillus Calmette Guerin (BCG). Sera of two main following groups were investigated in this study: sera samples from smear-positive, culture-positive and Tuberculin Skin Test-positive TB pa­tients and sera samples from smear-negative, culture negative and TST-nega­tive healthy individuals. Among the antigens used, BCG produced higher sensitivity and spe­cificity in the assay. With PPD as the solid phase, higher sensitivity, but lower specificity was observed in comparison with BCG. Both, low response and noise (non-specific binding) were observed with TB bacilli as the solid phase in the assay. Using BCG solid phase system in this method resulted in higher sensitivity in comparison to single antigen solid phase systems. In addition, we were able to circumvent the problem of non-specific bindings in more popular multi-antigenic solid systems such as PPD. By using this new indi­rect ELISA, a rapid, reliable and still inexpensive diagnosis of tuberculosis might be possible. Although, further investigations are required to confirm our result.