Single nucleotide polymorphism in Ag85 genes of Mycobacterium tuberculosis complex: analysis of 178 clinical isolates from China and 13 BCG strains

Exploring the immunogenicity of Rv2201-519: A T-cell epitope-based antigen derived from Mycobacterium tuberculosis AsnB with implications for tuberculosis infection detection and vaccine development

Research dedicated to diagnostic reagents and vaccine development for tuberculosis (TB) is challenging due to the paucity of immunodominant antigens that can predict disease risk and exhibit protective potential. Therefore, it is crucial to identify T-cell epitope-based Mycobacterium tuberculosis (MTB) antigens characterized by specific and prominent recognition by the immune system. In this study, we constructed a T-cell epitope-rich tripeptide-splicing fragment (nucleotide positions 131-194, 334-377, and 579-643) of Rv2201 (also known as the 72 kDa AsnB)from the MTB genome, ultimately yielding the recombinant protein Rv2201-519 in Escherichia coli BL21 (DE3). Subsequently, we gauged the recombinant protein's ability to detect tuberculosis infection through ELISpot and assessed its immunostimulatory effect on mouse models using flow cytometry and ELISA. Our results indicated that Rv2201-519 possessed promising sensitivity; however, the sensitivity was lower than that of a commercial diagnostic kit containing ESAT-6, CFP-10, and Rv3615c (80.56 % vs. 94.44 %). The Rv2201-519 group exhibited a propensity for a CD4+ Th1 cell immune response in inoculated BALB/c mice that manifested as higher levels of antigen-specific IgG production (IgG2a/IgG1 > 1). In comparison to Ag85B, Rv2201-519 induced a more robust Th1-type cellular immune response as evidenced by a notable rise in the ratio of IFN-γ/IL-4 and IL-12 cytokine production and increased CD4+ T cell activation with a higher percentage of CD4+IFN-γ+ T cells. Rv2201-519 also induced a higher level of IL-6 compared with Ag85B, a higher percentage of CD8+ T cells specific for Rv2201-519, and a lower percentage of CD8+IL-4+ T cells. Collectively, the current evidence suggests that Rv2201-519 could potentially serve as an immunodominant protein for tuberculosis infection screening, laying the groundwork for further evaluation in recombinant Bacillus Calmette-Guérin (BCG) and subunit vaccines against MTB challenges in future studies.

Diagnosis of osteoarticular tuberculosis by immuno-PCR assay based on mycobacterial antigen 85 complex detection

Diagnosis of osteoarticular tuberculosis (OATB) exhibits serious challenges owing to paucibacillary nature of specimens and localization of disease at sites that are difficult to access. We recently developed indirect immuno-PCR (I-PCR) and real-time I-PCR (RT-I-PCR) assays for the detection of mycobacterial antigen 85 complex (Ag85) in OATB patients. Detection limits for the purified Ag85 protein were found to be 1 and 41 fg ml^-1 by I-PCR and RT-I-PCR, respectively, which were at least 10⁵ -fold lower than respective ELISA. While spiking synovial fluids of non-TB control subjects with the purified Ag85 protein, LODs of 100 and 120 fg ml^-1 were obtained by I-PCR and RT-I-PCR, respectively, thus demonstrating the sample matrix effect. Sensitivities of 87·5 and 70·5% were observed in bodily fluids of confirmed (n = 8) and clinically suspected (n = 51) OATB cases, respectively, by I-PCR, with a specificity of 93·9% (n = 33). Markedly, the sensitivities obtained by I-PCR/RT-I-PCR were significantly higher (P < 0·05-0·01) than ELISA and GeneXpert assay (n = 30). However, no substantial difference in sensitivity was observed between the I-PCR and RT-I-PCR assays. After further improving the accuracy of I-PCR, this test may lead to development of an attractive diagnostic kit.

Weak spots inhibition in the Mycobacterium tuberculosis antigen 85C target for antitubercular drug design through selective irreversible covalent inhibitor-SER124

Mycobacterium tuberculosis (Mtb) encoded secreted antigen 85 enzymes (Ag85A/Ag85B/Ag85C) play that critical roles in the virulence, survival and drug-resistant TB of the pathogen. Ag85 proteins are potential antitubercular drug targets because they are essential in the catalytic synthesis of trehalose moieties and mycolic acid attachment to the Mtb cell wall. Recently, experimental protocols led to the discovery of a selective covalent Ag85 inhibitor, β-isomer monocyclic enolphosphorus Cycliphostin (CyC_8β) compound, which targets the Ag85 serine 124 to exhibit a promising therapeutic activity. For the first time, our study unravelled the structural features among Mtb Ag85C homologs and motions and dynamics of Ag85C when the CyC_8β bound covalently and in open model conformations to the protein using bioinformatics tools and integrated Molecular dynamics simulations. Comparative Ag85C sequence analysis revealed conserved regions; 70% active site, 90% Adeniyi loop L1 and 50% loop L2, which acts as a switch between open and closed conformations. The average C-α atoms RMSD (2.05 Å) and RMSF (0.9 Å) revealed instability and high induced flexibility in the CyC_8β covalent-bound compared to the apo and open model systems, which displayed more stability and lower fluctuations. DSSP showed structural transitions of α-helices to bend and loops to 3₁₀-helices in the bound systems. SASA of CyC_8β covalent bound showed active site hydrophobic residues exposure to huge solvent. Therefore, these findings present the potential opportunity hotspots in Ag85C protein that would aid the structure-based design of novel chemical entities capable of resulting in potent antitubercular drugs.Communicated by Ramaswamy H. Sarma.

EXPRESSION OF IMMUNOGLOBULIN, GRANZYME-B AND PERFORIN AGAINST Ag85A AND Ag85B PROTEINS OF MYCOBACTERIUM TUBERCULOSIS IN BALB/C MICE

Background:

Ag85 is a protein that may maintain survival of M. tuberculosis in intracellular parts of host cells and is considered as a virulence factor. The expression of Ag85 protein can stimulate proliferation and differentiation of B- cells and T-cells in patients with tuberculosis. This research aimed to determine the ability of Ag85A and Ag85B proteins in activating the response of antibodies, granzyme-B and perforin in Balb/c mice.

Materials and Methods:

Twenty-five male Balb/c mice were assigned into five groups. Group I was treated with adjuvant, group II with Bacillus Calmette-Guerin (BCG) vaccine, group III with a combination of BCG and Ag85A, group IV with a combination of BCG and Ag85B and group V with a combination of BCG, Ag85A and Ag85B. Concentrations of immunoglobulin G, granzyme-B and perforin were examined using ELISA and the number of CD8+ T-cells and NK T-cells were checked by flow cytometry.

Results:

The highest concentration of immunoglobulin G was found in group V with 62.49±5.4327 ng/ml. The highest mean number of CD8+ T-cells, NK T-cells, granzyme-B and perforin was found in group IV with 4.32%, 1.03%, 35.11±1.7789 pg/ml and 6.19±0.2235 pg/ml, respectively. The results of One-Way ANOVA test showed that there were significant differences in immunoglobulin responses, with p<0.05. The expressions of granzyme-B and perforin were higher in mice treated with combination of BCG and recombinant proteins.

Conclusions:

Ag85 protein can be combined with the BCG vaccine to improve protection against M. tuberculosis infection.