[Lymphocyte immunoreactivity in subjects vaccinated with Calmette-Guerin bacillus (BCG)]

PHA, Pokeweed and PPD lymphocytes transformation in vitro was studied in four groups of people. One group was negative to PPD skin testing; one was positive for a "naturally" acquired infection; the third group were people vaccinated with BCG in the last year; fourth group people vaccinated with BCG within one and five years. Last two groups had generally low or negative reaction to PPD skin test. PPD was used at different concentration, from 0.025 to 35 microgram/ml; maximum stimulation was at 1 microgram/ml. Stimulation index was lower in vaccinated people than in "natural" positive. Lymphocytes of people vaccinated from more than one year showed no difference from PPD negative people. Highly significant difference was observed between these two groups and people "naturally" positive and within one year of vaccination. We discuss our data and interpret the findings as showing that there are less PPD sensitive lymphocytes in patients vaccinated with BCG than in people with a "natural" infection and that this circulating population of lymphocytes disappears or decreases in the years following vaccination.