STUDIES OF HUMAN LEUKOCYTE CULTURE AS AN IN VITRO TEST OF DELAYED HYPERSENSITIVITY

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Abstract
The delayed cutaneous tuberculin hypersensitivity of 31 humans was correlated with the proliferative effect of PPD [purified protein derivative] on their blood leukocytes in short-term tissue culture. Employing the isotope H3TDR [tritiated thymidine], the degree of cellular proliferation was determined radio-autographically. Healthy persons with either negative or positive tuberculin skin tests and patients with active tuberculosis who reacted positively to tuberculin were studied. The mean proliferative response of the 2 groups with positive cutaneous reactions was equal and approximately 9 times that of the nonreactors; this difference was significant. Nevertheless, the incidence of false-negative in vitro reactors was 35%. False-positive in vitro results were infrequent, which may be related to the fact that none of the subjects studied was known to have received BCG vaccination. Persons requiring 2nd strength PPD for elicitation of a positive tuberculin skin test had leukocytes that were less reactive in vitro than those responding to intermediate-strength PPD, but the difference was not significant. No relationship could be demonstrated when the size of the skin test response of persons reacting to intermediate PPD was compared to the in vitro results. The relatively high incidence of false-negative culture results limits the usefulness of the leukocyte culture technique as an in vitro measure of delayed cutaneous hypersensitivity to tuberculin. The reasons for the imperfect correlation are not known and deserve further study.

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