Comparison of the early chromatin reaction of the mouse thymocytes incubated with phytohemagglutinin and concanavalin A.

The preliminary activation of mouse thymocytes in vitro following exposure to the mitogens phytohemagglutinin and Concanavalin A, was compared. For this purpose the ratio of the fluorescence intensity for acridine orange-DNA complex at light wave length gamma = 590 nm to the fluorescence intensity of this complex at light wave length gamma = 530 nm was determined. It was shown that 100% of thymocytes showed an increase in chromatin activity under the influence of Con A within 15 minutes of incubation, but that following incubation with PHA an increase in activity occurred only in 25% of cells and was detectable only after 60 minutes of incubation. The results show that differences in the reactivity of thymocytes to PHA and Con A concern not only the late steps of activation such as RNA, protein and DNA synthesis, but also involve the earliest responses to the mitogen. The observed differences are discussed and correlated with the different degrees of maturity of the thymocytes.