Response of human blood lymphocytes to tuberculin PPD in tissue culture.

Human lymphocyte suspensions containing more than 99.2 per cent small lymphocytes were prepared from peripheral blood using methyl cellulose and carbonyl iron. The human donors were skin tested with tuberculin PPD or tuberculin OT. Their lymphocytes were cultured in the presence of tuberculin PPD and the transformed cells which appeared in the cultures were accurately quantitated. When the corrected indices of response of lymphocyte cultures prepared from sensitized donors were plotted against the increasing amounts of tuberculin PPD used as a stimulus, a dose—response curve was obtained. The dose which gave the greatest distinction between lymphocytes from sensitized and from non-sensitized donors was 250 OT units of tuberculin PPD per ml of culture containing 2 × 106 small lymphocytes per ml. Analysis of the culture population at 20-hour intervals for 100 hours showed that the transformed cells seen in vitro were derived from small lymphocytes. Study of the behaviour of the stimulated cultures indicated that a 90-hour culture period was the most satisfactory for the accurate assessment of the immunological response. A correlation was established between the immunological status of the lymphocyte donor and the corrected index of response of his lymphocytes in vitro. Cultures from non-sensitized donors had a corrected index of response close to zero. Corrected indices of response from sensitized donors ranged from 2 to 94 depending on the sensitivity of the donor to tuberculin PPD.