Clinical value of specific detection of immune complex-bound antibodies in pulmonary tuberculosis

Two actively secreted (38 and 30 kDa) and 1 cytosolic (16 kDa) antigens were purified from Mycobacterium tuberculosis culture filtrate and cytosol, respectively, using a combination of chromatographic and electrophoretic methods. One recombinant antigen (27 kDa) overexpressed in Escherichia coli was also isolated. The diagnostic test characteristics of circulating immune complex (CIC)-bound antibodies to purified protein antigens, singly and in combination, were evaluated in patients with pulmonary tuberculosis. The individual antigens ranged in their sensitivity from 73% to 88%, while considering the IgG response. Addition of IgA results improved the sensitivity. The combination of IgG results for 38, 30, and 16 kDa offered >95% sensitivity and specificity for the smear- and culture-positive tuberculosis, as well as for the smear-negative, culture-positive group. CIC-bound antibodies promise to be a better diagnostic tool than serum antibodies.