title: Interferon-gamma responses after isoniazid chemotherapy for latent tuberculosis.
abstract: OBJECTIVE
  Chemotherapy for Mycobacterium tuberculosis infection may decrease interferon (IFN)-gamma responses to early secretory antigenic target 6 and culture filtrate protein (CFP)-10; a reaction that could be useful to monitor the success of treatment. We investigated IFN-gamma responses in subjects with latent TB infection before and after isoniazid (INH) chemotherapy.
  
  
  METHODS
  A total of 48 patients who had contact with a TB patient in a psychiatric hospital were suspected to have latent TB infection on the basis of a positive QuantiFERON-TB Gold (QFT-G) test and were offered INH treatment for 6 months. After INH chemotherapy, IFN-gamma responses were again quantified and compared with initial measurements.
  
  
  RESULTS
  Thirty-four patients completed 6 months of therapy and 28 were retested. Seven (25%) had a negative test and the other patients showed an overall decline. Geometric mean for early secretory antigenic target 6 decreased from 1.398 to 0.362 (P < 0.001), and that for CFP-10 from 0.312 to 0.120 (P < 0.001). A subsequent QFT-G test carried out 18 months after chemotherapy showed no further decline of IFN-gamma responses.
  
  
  CONCLUSIONS
  If the success of chemotherapy is defined as negative conversion in the QFT-G test, these results suggest that although the waning of QFT-G responses as a result of chemotherapy is an important characteristic of IFN-gamma responses, the extent of waning would not be sufficient to allow effective monitoring of the success of chemotherapy because a majority of contacts still showed positive responses in the QFT-G test even after chemotherapy.
authors.affiliation: Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, Tokyo, Japan. higuchi@jata.or.jp
authors.forename: Kazue
authors.initials: K
authors.lastname: Higuchi
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Harada
authors.forename: Toru
authors.initials: T
authors.lastname: Mori
mesh_terms: D000328:Adult; D000368:Aged; D000995:Antitubercular Agents / Q000627:therapeutic use*; D015415:Biomarkers / Q000097:blood; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000097:blood*; D007538:Isoniazid / Q000627:therapeutic use*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000502:physiology*; D012680:Sensitivity and Specificity; D014374:Tuberculin Test; D014376:Tuberculosis / Q000097:blood / Q000175:diagnosis / Q000188:drug therapy*; D017735:Virus Latency
chemical_list: D000995:Antitubercular Agents; D015415:Biomarkers; D007371:Interferon-gamma; D007538:Isoniazid