Multiple lymphocyte transformation tests by phytohemagglutinin in healthy individuals. Transient episodes of decreased lymphocyte blastogenesis

146 serial determinations of spontaneous and phytohemagglutinin-induced lymphocyte transformation as measured by tritiated thymidine incorporation, were performed in 24 healthy individuals. 9 persons were studied intensively during a mean period of 40 days and the other 15 underwent random investigations during a period up to 10 mth. Transient episodes of significant decreased lymphocyte transformation were revealed in 14 persons (58.4%) with regard to the spontaneous blastogenesis and in 11 subjects (45.8%) with regard to PHA-induced reactivity. The occurrence of the decreased values in PHA responsiveness was significantly higher in the intensively studied group compared to the randomly investigated one (p = 0.001). The probability of detecting 1 low PHA-related response in a normal subject was 11%. In only half of the cultures with low spontaneous blastogenic response did a simultaneous decrease in PHA-induced lymphocyte transformation occur. In addition to the currently used stimulation index, a new index termed the Blastogenic Cumulative Index is proposed. It is defined as the sum of the logarithms of the dpm values of the spontaneous and the PHA induced lymphocyte transformation. The CI is suggested to describe lymphocyte blastogenic function more accurately, and due to its simplicity warrants further study. Other indices for lymphocyte blastogenesis determination are discussed.