Rv1985c, a promising novel antigen for diagnosis of tuberculosis infection from BCG-vaccinated controls

Abstract

BackgroundAntigens encoded in the region of difference (RD) of Mycobacterium tuberculosis constitute a potential source of specific antigens for immunodiagnosis. In the present study, recombinant protein Rv1985c from RD2 was cloned, expressed, purified, immunologically characterized and investigated for its potentially diagnostic value for tuberculosis (TB) infection among BCG-vaccinated individuals.MethodsT-cell response to Rv1985c was evaluated by IFN-γ ELISPOT in 56 TB patients, 20 latent TB infection (LTBI) and 30 BCG-vaccinated controls in comparison with the commercial T-SPOT. TB kit. Humoral response was evaluated by ELISA in 117 TB patients, 45 LTBI and 67 BCG-vaccinated controls, including all those who had T-cell assay, in comparison with a commercial IgG kit.ResultsRv1985c was specifically recognized by cellular and humoral responses from both TB and LTBI groups compared with healthy controls. Rv1985c IgG-ELISA achieved 52% and 62% sensitivity respectively, which outperformed the sensitivity of PATHOZYME-MYCO kit (34%) in detecting active TB (P = 0.011), whereas IFN-γ Rv1985c-ELISPOT achieved 71% and 55% sensitivity in detecting active and LTBI, respectively. Addition of Rv1985c increased sensitivities of ESAT-6, CFP-10 and ESAT-6/CFP-10 combination in detecting TB from 82.1% to 89.2% (P = 0.125), 67.9% to 87.5% (P < 0.001) and 85.7% to 92.9% (P = 0.125), respectively.ConclusionsIn conclusion, Rv1985c is a novel antigen which can be used to immunologically diagnose TB infection along with other immunodominant antigens among BCG-vaccinated population.

Mycobacterium tuberculosis Region of Difference (RD) 2 Antigen Rv1985c and RD11 Antigen Rv3425 Have the Promising Potential To Distinguish Patients with Active Tuberculosis from M. bovis BCG-Vaccinated Individuals

“…Our result suggested that the sensitivity of the QFT-IT assay could be raised when it was used in combination with Rv1985c pool2 and Rv1985c pool4 , just as previous studies did (10,16,17). Though the additive effect on sensitivity was not statistically significant, the trend may be more obvious and relevant if tested on a broader scale.…”

“…PHA (2.5 g/ml) and saline were added as a positive control and a negative control, respectively. Peptide cocktails from ESAT-6, including ESAT-6 from residues 1 to 20 (ESAT-6 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] ), ESAT-6 42-65 , ESAT-6 52-75 , and ESAT-6 72-95 , were selected according to some other research (23,24) and tested as controls to evaluate the diagnostic performance of the selected peptide pools. On the basis of a dose-response curve ranging from 0 to 20 g/ml, the working concentration of the peptide mixtures was determined at the concentration with the strongest response, which was 1 g/ml per peptide.…”

“…The proteins encoded in the regions of differences (RDs) of M. tuberculosis have become the most promising candidates as diagnostic antigens. Our previous study demonstrated that recombinant antigens of Rv1985c and Rv3425 had great potential for specific immune-based diagnosis of TB infection in the BCG-vaccinated population (16,17). In this study, 25-amino-acid-long peptides covering the whole length of the two antigens were first tested for their ability to stimulate IFN-␥ release.…”

“…Rv1985c is a putative chromosome replication initiation inhibitor protein which was specifically recognized by both cellular and humoral responses from patients with TB (17). Rv3425 is a member of the proline-proline-glutamate (PPE) family and was found to be a promising antigen in the serodiagnosis of TB (18,19).…”

“…To search for novel antigens with diagnostic potential, we screened several recombinant RD2 and RD11 antigens for their ability to induce an antigen-specific T-cell response and found that RD2 antigen Rv1985c and RD11 antigen Rv3425 have good diagnostic potential (16,17). Rv1985c is a putative chromosome replication initiation inhibitor protein which was specifically recognized by both cellular and humoral responses from patients with TB (17).…”