Qualitative and quantitative analysis of antibody response in childhood tuberculosis against antigens of Mycobacterium tuberculosis.

PURPOSE Serodiagnosis of tuberculosis in children, using available crude antigens, has been difficult. The tests lack sufficient sensitivity and/or specificity. In this study, western blot analysis of M. tuberculosis H37Rv culture filtrate antigen (CFA) was carried out, to identify diagnostically useful antigens. In addition, the CFA was also used in enzyme linked immunosorbent assay (ELISA), to measure antibodies of multiple isotypes. METHODS Specific IgG, IgA and IgM antibodies were estimated in the sera from 26 clinically/bacteriologically diagnosed cases of childhood tuberculosis (CTB) and 61 normal children (CNHS), using culture filtrate antigen. Western blot analysis with culture filtrate antigen was carried out to qualitatively compare the antibody profile among the CTB, with childhood normal controls and adult TB. RESULTS IgG positivity was only 7.6% with culture filtrate antigen in the CTB group, while 3.2% among the controls were also positive. However, the results of IgA and IgM isotypes were better. By combination of all the three isotypes an increased sensitivity of 57.7% with a specificity of 93.5%, was obtained. Immunoblot analysis revealed marked difference among antibodies in the region of 16, 19, 38 and 45 kDa between CTB and CNHS. CONCLUSIONS Our findings point to a limited sensitivity of 57.7% in ELISA with culture filtrate antigen. However, antibodies around 16, 19, 38 and 45 kDa region may be useful in differentiating the CTB patients from CNHS by immunoblot assay.