Immunoglobulin G response to mammalian cell entry 1A (Mce1A) protein as biomarker of active tuberculosis.

Cell wall components are major determinants of virulence of Mycobacterium tuberculosis and they contribute to the induction of both humoral and cell-mediated immune response. The mammalian cell entry protein 1A (Mce1A), in the cell wall of M. tuberculosis, mediates entry of the pathogen into mammalian cells. Here, we examined serum immunoglobulin levels (IgA, IgM and total IgG) against Mce1A as a potential biomarker for diagnosis and monitoring tuberculosis (TB) treatment response. Serum samples of 39 pulmonary TB patients and 65 controls (15 healthy household contacts, 19 latently infected household contacts, 13 non-TB and 18 leprosy patients) were screened by ELISA. The median levels of all immunoglobulin classes were significantly higher in TB patients when compared with control groups. The positive test results for IgA, IgM and total IgG were 62, 54 and 82%, respectively. For comparison, routine sputum smear examination diagnosed only 26 (67%) of 39 TB cases. Sensitivities of IgA, IgM and IgG test were 59, 51.3 and 79.5%, respectively, while the specificities observed were 77.3, 83.3 and 84.4%, respectively. A significant decrease compared with baseline was also shown after TB treatment. These results suggest that circulating total IgG antibody to Mce1A could be a complementary tool to diagnosis pulmonary TB.