Characteristic profile of antibody responses to PPD, ESAT-6, and CFP-10 of Mycobacterium tuberculosis in pulmonary tuberculosis suspected cases in Surabaya, Indonesia

Establishment of an indirect ELISA for Mycobacterium tuberculosis MTB39A protein antibody

The MTB39A protein is a member of the unique Mycobacterium tuberculosis (MTB) PE/PPE protein family and is the main candidate for tuberculosis (TB) diagnosis. The aim of this study was to establish a novel indirect ELISA (iELISA) method that uses antibodies against MTB. The MTB39A gene sequence was synthesized according to the MTB39A nucleotide sequence of the MTB H37Rv strain (GenBank accession number: NC_000962.3) and cloned into the pET28a( +) vector. After correct sequencing, it was transferred to Escherichia coli BL21 (DE3) receptor cells for expression and purification, and the purified recombinant protein was identified by SDS-PAGE and western blotting. The purified MTB39A protein was used as the capture antibody, and a rabbit polyclonal antibody against the MTB MTB39A protein was used as the detection antibody to establish an indirect ELISA method. The ELISA conditions were optimized, and the optimal coating concentration of the MTB39A antigen was determined to be 0.5 μg/mL. The optimal dilution of MTB39A rabbit polyclonal antibody was 1:4096, and the optimal dilution of HRP-goat anti-rabbit IgG was 1:4000. The results showed that this indirect ELISA method has high sensitivity, specificity and efficacy for MTB39A protein detection. Moreover, this indirect ELISA method has optimal stability and can be used for the initial detection of MTB antibodies in clinical human and bovine serum samples. The establishment of this assay provides a new method for the rapid diagnosis of MTB and technical support for the prevention and control of tuberculosis. KEY POINTS: • MTB MTB39A protein was expressed in a prokaryotic expression system. • Rabbit polyclonal antibody against MTB39A was prepared. • To establish an iELISA based on the MTB39A protein for the detection of MTB antibodies.

Antibodies against native proteins of Mycobacterium tuberculosis can detect pulmonary tuberculosis patients

Accurate point-of-care testing (POCT) is critical for managing tuberculosis (TB). However, current antibody-based diagnosis shows low specificity and sensitivity. To find proper antigen candidates for TB diagnosis by antibodies, we assessed IgGs responsiveness to Mycobacterium tuberculosis proteins in pulmonary TB (PTB) patients. We employed major secreted proteins, such as Rv1860, Ag85C, PstS1, Rv2878c, Ag85B, and Rv1926c that were directly purified from M. tuberculosis. In the first screening, we found that IgG levels were significantly elevated in PTB patients only against Rv1860, PstS1, and Ag85B among tested antigens. However, recombinant PstS1 and Ag85B from Escherichia coli (E. coli) couldn't distinguish PTB patients and healthy controls (HC). Recombinant Rv1860 was not checked due to its little expression. Then, the 59 confirmed PTB patients from Soetomo General Academic Hospital, Surabaya, Indonesia, and 102 HC were tested to Rv1860 and Ag85B only due to the low yield of the PstS1 from M. tuberculosis. The ROC analysis using native Ag85B and Rv1860 showed an acceptable area under curve for diagnosis, which is 0.812 (95% CI 0.734-0.890, p < 0.0001) and 0.821 (95% CI 0.752-0.890, p < 0.0001). This study indicates that taking consideration of native protein structure is key in developing TB's POCT by antibody-based diagnosis.

The role of antibodies in tuberculosis diagnosis, prophylaxis and therapy: a review from the ESGMYC study group

Tuberculosis (TB) is still responsible for the deaths of >1 million people yearly worldwide, and therefore its correct diagnosis is one of the key components of any TB eradication programme. However, current TB diagnostic tests have many limitations, and improved diagnostic accuracy is urgently needed. To improve the diagnostic performance of traditional serology, a combination of different Mycobacterium tuberculosis (MTB) antigens and different antibody isotypes has been suggested, with some showing promising performance for the diagnosis of active TB. Given the incomplete protection conferred by bacille Calmette-Guérin (BCG) vaccination against adult pulmonary TB, efforts to discover novel TB vaccines are ongoing. Efficacy studies from advanced TB vaccines designed to stimulate cell-mediated immunity failed to show protection, suggesting that they may not be sufficient and warranting the need for other types of immunity. The role of antibodies as tools for TB therapy, TB diagnosis and TB vaccine design is discussed. Finally, we propose that the inclusion of antibody-based TB vaccines in current clinical trials may be advisable to improve protection.

Immunological Characterization of Proteins Expressed by Genes Located in Mycobacterium tuberculosis-Specific Genomic Regions Encoding the ESAT6-like Proteins

The 6 kDa early secreted antigen target (ESAT6) is a low molecular weight and highly immunogenic protein of Mycobacterium tuberculosis with relevance in the diagnosis of tuberculosis and subunit vaccine development. The gene encoding the ESAT6 protein is located in the M. tuberculosis-specific genomic region known as the region of difference (RD)1. There are 11 M. tuberculosis-specific RDs absent in all of the vaccine strains of BCG, and three of them (RD1, RD7, and RD9) encode immunodominant proteins. Each of these RDs has genes for a pair of ESAT6-like proteins. The immunological characterizations of all the possible proteins encoded by genes in RD1, RD7 and RD9 have shown that, besides ESAT-6 like proteins, several other proteins are major antigens useful for the development of subunit vaccines to substitute or supplement BCG. Furthermore, some of these proteins may replace the purified protein derivative of M. tuberculosis in the specific diagnosis of tuberculosis by using interferon-gamma release assays and/or tuberculin-type skin tests. At least three subunit vaccine candidates containing ESAT6-like proteins as antigen components of multimeric proteins have shown efficacy in phase 1 and phase II clinical trials in humans.