Dissociation between humoral and cellular responses to PPD after BCG vaccination

Following repeated BCG vaccination, some people exhibited negative skin tests to tuberculin (PPD) but showed antibody titers similar to those observed in skin test positive people. The purpose of the experiments reported here was to analyze this dissociation observed between cellular and humoral response to tuberculin. Leukocytes from skin test negative people were normally stimulated by various mitogens but not by PPD. After separation of leukocytes into adherent and nonadherent cell populations and in vitro transfer experiments, it was shown that the nonadherent cell population was responsible for the nonresponsiveness to PPD. On the other hand, serum immunoglobulin levels and anti-PPD antibody titers were similar to those observed in skin test positive people. The results show that in skin test negative people, T cells involved in cellular immune response to PPD are ineffective while macrophages, helper T cells and B lymphocytes seem to function normally.