ABSTRACT
Since there are no reliable methods to demonstrate the effect of BCG vaccination in children, culture filtrates of BCG were evaluated for their specificity and sensitivity. BCG culture filtrate (BCG-CF), BCG sonicate and tuberculin were used as antigens and tested against serum, for the presence of IgG class of antibodies by ELISA and Western blot. Methodology: Children in the age-group of 1 to 10 years, were categorized as: (a) normal, and vaccinated, n=35; (b) normal, without a scar and with no evident history of vaccination, n=15; and (c) children with tuberculosis (meningitis, miliary and lymphadenitis) n=15. Results: The mean values of optical density (OD) in group (a), 4.0+0.08, were significantly high (P<0.001) to BCG-CF, compared to that of groups (b) (1.0+0.02) and (c) (1.4+0.03). The Western blot results revealed that a greater number of children (71%) in the vaccinated group reacted to low molecular weight proteins (10-30kDa) compared to other groups (unvaccinated: 17% and TB: 20%). The overall specificity, sensitivity, positive predictive value and negative predictive value of BCG-CF were higher in the vaccinated group. Conclusions: The results of the study suggest that the secreted antigens of BCG induce antibody formation, which are specific and are directed mostly towards the low molecular weight proteins. The presence of these antibodies could probably be exploited in an assay to distinguish children immunized by BCG from the unvaccinated and those having tuberculosis.