The antigenic structure of Mycobacterium tuberculosis examined by immunoblot and ELISA. Influence of the age of the culture and of the obtaining method on the composition of the antigenic extracts.

In this study we have examined by immunoblot (IB) and enzyme-linked immunosorbent assay (ELISA) the humoral immune response in pulmonary tuberculosis. As a previous step, in an attempt to obtain the optimal antigen preparation for these studies, the influence of the culture age and of the obtention method on the composition of the extracts was analyzed. The highest number of antigenic bands was found in culture filtrates of 6 and 8 weeks; at these times two thick bands of 65 and 63 kilodaltons (kDa) were identified. These bands were absent from younger and older cultures. When analyzing the source of antigens, we found that culture filtrates contained more antigenic bands than sonic extracts. In view of these findings, culture filtrates of 6 weeks of age were used as test antigens. With 19 tuberculous sera a total of 16 antigenic bands were observed by IB. The response was very heterogeneous with respect to the intensity of the detected reactions and the number of reacting bands. The most frequently recognized bands were those of 31, 32, 38, 58 and 94 kDa. By ELISA with 49 tuberculous sera and with 48 control sera, a specificity of 0.98 and a sensitivity of 0.70 were obtained.