Evaluation of Gamma Interferon Immune Response Elicited by the Newly Constructed PstS-1(285-374):CFP10 Fusion Protein To Detect Mycobacterium tuberculosis Infection

Abstract

The PstS1 antigen is highly immunogenic, principally when combined with CFP10 during both latent and active TB infection. In the present study, a selected pstS1 gene fragment was cloned, fused with CFP10, and expressed in Escherichia coli. The product M ycobacterium tuberculosis, a highly successful parasite, is the cause of tuberculosis (TB). A major health care concern, the disease results in approximately 1.4 million annual deaths (990,000 among HIV-negative individuals), infecting roughly one-third of the world's population. Among the infected, 5% to 10% will develop active disease in their lifetimes and 90% will harbor the latent form. According to a recent mathematical projection of TB eradication, the treatment of latent TB infection (LTBI) and active TB is urgently required in order to lower and ultimately prevent the further spread of the disease at its present rate (1, 2).Two principal approaches based on the adaptive immune responses elicited by M. tuberculosis infection are currently used to identify TBI (3): the in vivo tuberculin skin test (TST) and the ex vivo gamma interferon (IFN-␥) release assay (IGRA).Developed in 1908, TST became the standard means of assessing the presence of TB infection. Via TST, prior TB exposure is measured by a type 4 delayed-type hypersensitivity reaction when a purified protein derivative (PPD) of M. tuberculosis is injected intradermally. Although TST has some biological limitations such as the occurrence of anergies in one-third of active TB cases, crossreactivity with M. bovis bacillus Calmette-Guérin (BCG) and non-TB mycobacteria does not, according to some authors, result in major sensibility differences in IGRAs (4).The IGRA was recently developed using antigens that are expressed in M. tuberculosis but not in BCG or M. bovis strains as stimuli. These antigens measure the production of IFN-␥ in peripheral blood mononuclear cells (3,5). According to a recent World Health Organization (WHO) report (1), the two currently commercially available IGRAs have yet to generate sufficient data or enough high-quality evidence regarding their performance in the low-and middle-income countries that typically have a high TB and/or HIV burden and where the coverage of BCG vaccination may cause some interference (5, 6).Both IGRAs are based on Mycobacterium tuberculosis-specific antigens, namely, early secretory antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP10) (5). These antigens must be validated in different scenarios, but other antigen combinations also need to be evaluated to improve IGRA coverage.The 38-kDa M. tuberculosis antigen, also known as phosphatespecific transporter-1 (PstS-1), coded by a pstS1 gene that composes one of the 3 putative pst operons, is a lipoprotein phosphate transport receptor on the cell surface. These operons probably constitute a subtle biochemical adaptation of M. tuberculosis, enabling it to grow and survive under different phosphate-limiting conditions during its infectious cycle. The PstS-1 protein is ac-

Transcriptomic Biomarkers for Tuberculosis: Evaluation of DOCK9. EPHA4, and NPC2 mRNA Expression in Peripheral Blood

“…For the pilot RNAseq investigation a group of rCt from the Brazilian cohort was stratified according to the response to both TST and in house interferon-gamma release assays (IGRAs) under ESAT6:CFP10 stimulation (Araujo et al, 2014). Control and LTBI groups comprised 12 and 16 participants with TST neg /IGRA neg or TST pos /IGRA pos , respectively.…”

Close contact interferon-gamma response to the new PstS1(285–374):CPF10: a preliminary 1-year follow-up study

“…The present investigation was carried out on samples previously collected by the TB Control Program at the Clementino Fraga Filho University Hospital in Rio de Janeiro, RJ, Brazil [13]. All rCt recruited between March 2010 and August 2012 were >17 years of age and tested negatively for the human immunodeficiency virus (HIV).…”

“…All rCt recruited between March 2010 and August 2012 were >17 years of age and tested negatively for the human immunodeficiency virus (HIV). Upon obtaining informed oral and written consent, blood samples were collected prior to administering the Mantoux TST [13]. …”

“…Among LTBI, in comparison to the traditional ESAT6:CFP10, our new chimeric protein has demonstrated similar immunoreactivity while slightly increasing the detection of TST positive (TST pos ) rCt by both WBA and LSA [13]. This new protein was also able to identify an incident case that progressed from LTBI to active pulmonary TB within a short period in the absence of a response to LSA-ESAT6:CFP10 [13].…”

“…Among LTBI, in comparison to the traditional ESAT6:CFP10, our new chimeric protein has demonstrated similar immunoreactivity while slightly increasing the detection of TST positive (TST pos ) rCt by both WBA and LSA [13]. This new protein was also able to identify an incident case that progressed from LTBI to active pulmonary TB within a short period in the absence of a response to LSA-ESAT6:CFP10 [13]. As both TST and IGRA RD1-based have their limitations, continued surveillance of host immunomodulatory changes for a specific length of time, and especially after recent Mtb exposure, may result in revealing new antigens that could potentially be used to either compose new diagnostic tests or augment the effectiveness of current ones.…”