The tuberculin skin test in relation to immunological in vitro reactions in BCG-vaccinated healthcare workers.

The aim was to study the tuberculin skin test in relation to immunological in vitro reactions in bacille Calmette-Guerin (BCG)-vaccinated healthcare workers. The present study was performed in Sweden, a country with a low incidence of tuberculosis, a high BCG vaccination efficacy and high tuberculin conversion rates. BCG-vaccinated healthcare workers (n=381) were tuberculin skin tested. From these, 11 subjects with negative tuberculin reactions (<6 mm) were matched for age and sex with 11 subjects with large positive reactions (> or = 15 mm). Lymphocyte transformation and the production of interferon-gamma (IFN-gamma) were analysed after stimulation in vitro of peripheral blood mononuclear cells with tuberculin purified protein derivative, heat-killed tubercle bacilli and a culture filtrate from tubercle bacilli. In the tuberculin-positive group the lymphocyte transformation response was 2-3 times larger, and IFN-gamma production was 7-10 times larger, than in the tuberculin-negative group (p<0.001). The present results suggest that a positive tuberculin skin test in bacille Calmette-Guerin-vaccinated subjects indicates a stronger immune response of the protective T-helper 1-type than does a negative test. In similar settings, the study supports the traditional practice of regarding the tuberculin skin test in bacille Calmette-Guerin-vaccinated subjects as an indicator of a protective immune response against tuberculosis.