Effect of levamisole on the mitosis of murine thymocytes in culture

The effect of levamisole on murine thymocytes stimulated by concanavalin A in culture was measured as the change in number of cells in the DNA synthetic phase (S-phase) and in number of cells undergoing mitosis (M-phase). Addition of levamisole to Con A-stimulated lymphocytes led to an approximately tenfold increase in the frequency of mitosis and a fivefold increase in the frequency of cells heavily labeled with thymidine. Thus, levamisole leads to an increased number of cells undergoing proliferation. Determination of cell viability excluded the possibility that the effect of levamisole was simply due to enhanced numbers of viable cells in culture. Examining the effect of levamisole on the proliferating cells alone, it was found that they had a shorter cell cycle time. It was therefore concluded that levamisole affects thymocyte proliferation in vitro in two ways: enhancement of the number of proliferating cells and shortening the cell cycle time of proliferating cells. A similar effect in vivo might be important in the mechanism of action of levamisole as an immunotherapeutic agent.