Detection of tuberculous IgG antibodies using Mycobacterium tuberculosis H37Ra, excretory secretory antigen and tuberculin-purified protein derivative.

Different antigen preparations, viz. excretory-secretory antigen (ES Ag), phosphate buffer saline soluble antigen (PBS-S Ag) and sodium dodecyl sulphate soluble antigen (SDS-S Ag) of M. tuberculosis (M.tb) H37Ra strain along with tuberculin purified protein derivative (PPD) were employed in stick indirect ELISA to detect IgG antibodies in sera of sputum positive pulmonary tuberculosis cases. Sera from healthy individuals and individuals with diseases other than tuberculosis (cross-reacting diseases) were used as controls. ES antigen and PPD showed higher antibody titres in tuberculosis cases (GMT-1378 each) compared to PBS-S Ag (GMT-454) and SDS-S Ag (GMT-974). Thereafter, an extensive study was done analysing higher number of sera in each group for the detection of tuberculous IgG antibodies using ES Ag and PPD. The ES Ag showed better sensitivity (87%) and specificity (85%) compared to the sensitivity (73%) and specificity (78%) achieved with PPD. The ES Ag also showed higher IgG antibody titre (GMT-1068) than PPD (GMT-721). From the present study it can be envisaged that ES Ag has high diagnostic potential in tuberculosis.