Persistence of in vitro lymphocyte response to tuberculin skin test negative children immunized with BCG in infancy.

PPD stimulated lymphocyte reactivity was tested in 119 children aged 11 to 12 years. The lymphocyte responses was evaluated by measuring the extent of tritiated thymidine incorporation by cultured cells. In a group of sixty-four tuberculin negative children who had been BCG vaccinated in the neonatal period, lymphocyte response was significantly greater than in a group of non-vaccinated tuberculin negative children matched for sex. The highest reactivity appeared in another group of children vaccinated in infancy and tuberculin positive. Lymphocytes from BCG vaccinated children retain some sensitivity to tuberculin even years after the BCG vaccination and even at the time when the skin reactivity disappeared.