Abstract
Summary
The effect of cytosine arabinoside, an inhibitor of DNA synthesis, upon the primary induction of plaque-forming, anti-body-producing cells to sheep erythrocytes was investigated using mouse spleen fragments in vitro. It was found: (i) During the first 12 hr, following antigenic stimulation, the immune response proceeded undisturbed by the presence of the drug, (ii) If the inhibitor was permitted to act for the first 18 hr, the number of plaque-forming cells was reduced to 63% of control values. (iii) Extension of the period of action of the drug to the first 24 hr further reduced the number of plaque-forming cells to 33%, and if the inhibitor was allowed to act for the first 48 hr, total suppression of the immune response was observed. These findings indicate that DNA synthesis, essential for the undisturbed progression of the primary immune response as observed in the system employed, is initiated about the eighteenth hour after antigenic stimulation.
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