Decreased in vitro incorporation of 3H-thymidine into spleen cell DNA of antigenically stimulated rabbits treated in the postnatal period with nucleic acid from adult donors.

Spleen cell DNA from 6-month-old rabbits, that has received the first dose of soluble HSA antigen at 9 days of age and the second at 2 months of age and did not form antibodies incorporated 3H-thymidine in vitro as early as 1 hour after restimulation of rabbits with HSA antigen in vivo. The incorporation rate (in muCi/mg.) of isolated cellular DNA was higher than that of DNA from rabbits that had been pretreated with nuclear DNA from the spleens of adult non-immunized rabbits or from the spleens of pigs immunized with a different antigen (DNP-BGG), 4-5 days before the first dose of antigen. The inhibitory effect of pig DNA was stronger. Decreased incorporation of DNA was noted at 8 hours after restimulation of rabbits treated in the same manner as the previous group. The difference between the incorporation rate at 1 hour and at 8 hours after the restimulation was most marked in the DNA obtained from rabbits not treated with nuclear DNA in the postnatal period. The activity of lymphoid cell DNA after antigenic stimulation is discussed.