Isotype-specific Anti-38 and 27 kDa (mpt 51) Response in Pulmonary Tuberculosis with Human Immunodeficiency Virus Coinfection

Abstract

There is a need for rapid diagnostic methods to identify tuberculosis among human immunodeficiency virus-positive cases (HIV-TB). This study evaluated the serodiagnostic potential of the native 38 kDa and recombinant 27 kDa (mpt 51) antigens of Mycobacterium tuberculosis purified in the laboratory, when applied to HIV-TB patients. The antibody response was studied using enzyme-linked immunosorbent assays (ELISA). In the HIV-TB group, anti-38 kDa antibody of the immunoglobulin G (IgG), IgA and IgM isotypes was found in 38%, 43% and 7% of patients, respectively. Antibodies to the 27 kDa antigen occurred in 50%, 31% and 1% for IgG, IgA and IgM, respectively. The sensitivity increased upon combination of the results of IgG and IgA isotypes for each of the antigens, without compromising specificity. When the results were analysed based on the smear positivity, 71-78% and 54-69% were positive among smear-positive and smear-negative HIV-TB cases, respectively. A higher sensitivity (71% and 69%) was obtained using the 27 kDa antigen. The use of both antigens offered a sensitivity of 82% in smear-positive and 69% in smear-negative cases. There was no difference in antibody response among the HIV-TB cases, related to CD4 counts. Thus, the combination of the 38 and 27 kDa (mpt 51) antigens proved to be of diagnostic utility in HIV-TB, irrespective of the severity of immunosuppression, in smear-positive and smear-negative TB.