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.

This investigation was supported by Research Grant C-4027 from the National Cancer Institute, U. S. Public Health Service, and by an American Cancer Society institutional research grant.


A report on part of this work was presented at the Federation Meetings, April 14, 1959.

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