title: New tools for detecting latent tuberculosis infection: evaluation of RD1-specific long-term response.
abstract: BACKGROUND
  Interferon-gamma (IFN-gamma) release assays (IGRAs) were designed to detect latent tuberculosis infection (LTBI). However, discrepancies were found between the tuberculin skin test (TST) and IGRAs results that cannot be attributed to prior Bacille Calmètte Guerin vaccinations. The aim of this study was to evaluate tools for improving LTBI diagnosis by analyzing the IFN-gamma response to RD1 proteins in prolonged (long-term response) whole blood tests in those subjects resulting negative to assays such as QuantiFERON-TB Gold In tube (QFT-IT).
  
  
  METHODS
  The study population included 106 healthy TST+ individuals with suspected LTBI (recent contact of smear-positive TB and homeless) consecutively enrolled. As controls, 13 healthy subjects unexposed to M. tuberculosis (TST-, QFT-IT-) and 29 subjects with cured pulmonary TB were enrolled. IFN-gamma whole blood response to RD1 proteins and QFT-IT were evaluated at day 1 post-culture. A prolonged test evaluating long-term IFN-gamma response (7-day) to RD1 proteins in diluted whole blood was performed.
  
  
  RESULTS
  Among the enrolled TST+ subjects with suspected LTBI, 70/106 (66.0%) responded to QFT-IT and 64/106 (60.3%) to RD1 proteins at day 1. To evaluate whether a prolonged test could improve the detection of LTBI, we set up the test using cured TB patients (with a microbiologically diagnosed past pulmonary disease) who resulted QFT-IT-negative and healthy controls as comparator groups. Using this assay, a statistically significant difference was found between IFN-gamma levels in cured TB patients compared to healthy controls (p < 0.006). Based on these data, we constructed a receiver operating characteristic (ROC) curve and we calculated a cut-off. Based on the cut-off value, we found that among the 36 enrolled TST+ subjects with suspected LTBI not responding to QFT-IT, a long term response to RD1 proteins was detected in 11 subjects (30.6%).
  
  
  CONCLUSIONS
  These results indicate that IFN-gamma long-term response to M. tuberculosis RD1 antigens may be used to detect past infection with M. tuberculosis and may help to identify additional individuals with LTBI who resulted negative in the short-term tests. These data may provide useful information for improving immunodiagnostic tests for tuberculosis infection, especially in individuals at high risk for active TB.
authors.affiliation: Department of Epidemiology and Preclinical Research, L. Spallanzani National Institute for Infectious Diseases, IRCCS, Rome, Italy. ornella.butera@inmi.it
authors.forename: Ornella
authors.initials: O
authors.lastname: Butera
authors.forename: Teresa
authors.initials: T
authors.lastname: Chiacchio
authors.forename: Stefania
authors.initials: S
authors.lastname: Carrara
authors.forename: Rita
authors.initials: R
authors.lastname: Casetti
authors.forename: Valentina
authors.initials: V
authors.lastname: Vanini
authors.forename: Serena
authors.initials: S
authors.lastname: Meraviglia
authors.forename: Giuliana
authors.initials: G
authors.lastname: Guggino
authors.forename: Francesco
authors.initials: F
authors.lastname: Dieli
authors.forename: Marco
authors.initials: M
authors.lastname: Vecchi
authors.forename: Francesco N
authors.initials: FN
authors.lastname: Lauria
authors.forename: Almerico
authors.initials: A
authors.lastname: Marruchella
authors.forename: Patrizia
authors.initials: P
authors.lastname: Laurenti
authors.forename: Mahavir
authors.initials: M
authors.lastname: Singh
authors.forename: Nadia
authors.initials: N
authors.lastname: Caccamo
authors.forename: Enrico
authors.initials: E
authors.lastname: Girardi
authors.forename: Delia
authors.initials: D
authors.lastname: Goletti
mesh_terms: D000328:Adult; D000942:Antigens, Bacterial / Q000097:blood* / Q000276:immunology; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000097:blood* / Q000276:immunology; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification; D011933:Reagent Kits, Diagnostic; D014374:Tuberculin Test / Q000379:methods; D055815:Young Adult
chemical_list: D000942:Antigens, Bacterial; D011933:Reagent Kits, Diagnostic; D007371:Interferon-gamma