Prednisolone Inhibition of DNA Synthesis by Human Lymphocytes Induced in vitro by Phytohaemagglutinin

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Abstract
The effect of a wide range of concentration of prednisolone 21 phosphate on the transformation of normal human peripheral lymphocytes produced by 72 hr cultures with phytohemagglutinin (PHA) was studied by an objective radioactive technique utilizing the ability of the transformed lymphocytes to synthesize DNA and incorporate tritiated thymidine prior to undergoing mitosis. Prednisolone at a concentration of 1 [mu]g/ml did not inhibit this transformation. Inhibition occurred in the presence of prednisolone at concentrations of 5 to 1000 [mu]g/ml, there being a linear relationship between the degree of inhibition and the log concentration of steroid. The effect of delay in exposure to the steroid was studied. Inhibition of PHA induced synthesis of DNA occurred when 10 [mu]g of prednisolone per ml was added 24 and 48 hr after the PHA and when 800 [mu]g of prednisolone per ml was added 24, 48, 68 and 70 hr after the PHA. Morphological lymphocyte transformation was apparently normal in cultures exposed to 800 [mu]g of prednisolone per ml for their final 2 hr whereas there was a diminution in the degree of nuclear labelling and in the quantitative uptake of tritiated thymidine. This suggests that the steroid was specifically inhibiting DNA synthesis.

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