Antibody response in pulmonary tuberculosis against recombinant 27kDa (MPT51, Rv3803c) protein of Mycobacterium tuberculosis

The objective of this study is to evaluate the recombinant 27kDa (MPT51, Rv3803c) antigen of M. tuberculosis H37Rv, expressed in E. coli in enzyme linked immunosorbent assays (ELISA) to estimate the IgG, IgA and IgM levels in sera from adult pulmonary tuberculosis patients and control groups. Sera from smear and culture positive tuberculosis patients (S+C+) were positive for anti-MPT51 IgG, IgA and IgM, with a sensitivity of 57%, 47% and 13%, respectively. The sensitivity of the test improved to a level of 71% for IgG+IgA without significantly compromising the specificity (IgG of 98%, IgG+IgA of 95%). Addition of IgM results did not enhance the sensitivity appreciably, over and above that of IgG+IgA (72% vs 71%). Among the smear-negative but culture-positive cases (S-C+), 34% were positive for IgG, while in smear and culture-negative but X-ray-positive cases (S-C+), 42% were positive for IgG. Polyethylene glycol precipitation (PEG) of the circulating immune complex (CIC) in sera was carried out. The CIC-bound antibodies to MPT51 were assessed using ELISA. Measuring the IgG+IgA combination positivities of the CIC-bound antibodies gave a poor sensitivity of 21%, 18% and 10%, respectively. The specificity of the assay by these combinations was maintained at 94%.