Incorporation of iododeoxyuridine into cellular deoxyribonucleic acid synthesized after infection with simian virus 40

Primary monkey kidney cells (Cerocpithecus aethiops) in the stationary phase of growth were labeled with (14)C-thymidine for 24 hr prior to infection with simian virus 40 (strain 777). (3)H-deoxyadenosine and 5-iodo-2'-deoxyuridine (IUdR) were added to some of the cultures 24, 48, or 72 hr after infection; 24 hr later the deoxyribonucleic acid (DNA) was extracted from these cultures and centrifuged in a CsCl density gradient. The portion of DNA which had become heavier because of incorporation of IUdR could be seen as a second peak in the sedimentation profile. This peak contained (14)C as well as (3)H activity. The possibility that the (14)C-labeled cellular DNA might be degraded and used for the synthesis of viral DNA could be excluded. On the basis of these results, it must be assumed that the infection of monkey kidney cells with simian virus 40 induces the synthesis of cellular DNA.

Homotransplantation Immunity and Tolerance in the Bullfrog

The bullfrog, Rana catesbeiana, is capable of giving a vigorous isoimmune response to skin homografts, both as a larva and as an adult. First-set skin homografts showed the same median survival times (11.8 ± 0.6 to 13.6 ± 1.0 days) at 25°C on animals ranging in age from 2 months to 2 years. There was likewise no significant difference in MST's of grafts to larvae at progressive stages of development from stage 25 to maturity. Thus the isoimmune response capacity once developed remains essentially unchanged whatever the age or stage of development, despite the fact that profound physiologic changes occur during metamorphosis. Second-set homografts among these larvae evoked an anamnestic reaction evidenced by an MST of only 5.1 ± 0.3 days at 25°C. Homografts survived about three times as long at 15°C, revealing the temperature dependence of the homograft reaction in this poikilothermic species.

Many newly-hatched larvae at stage 24 and up to 36 days of age were sufficiently immature to become partially or completely tolerant toward homografts. A 68 days-old group of larvae at stage 25 showed a diminished homograft reaction, possibly associated with a transition from the tolerance to immune type of response. Beyond this age and stage complete immunologic maturity was manifest.

Immunologic specificity in rejection and tolerance was determined by the responses to homografts from different second donors. The finding that nine skin homografts showed prolonged survival as a result of a previous tailbud homograft from a different donor is evidence that the current concept of strict individual specificity in tolerance may be erroneous.