Chimeric and Ex-parabiotic Frogs (Rana Pipiens): Specificity of Tolerance

Rejection of orthotopic neural-fold transplants may be prevented by either embryonic parabiosis or reciprocal exchange of presumptive blood. These observations form the basis of the no blood-no tolerance hypothesis, which states that persistent tolerance by the host requires that the somatic transplant be accompanied by presumptive blood from the donor. Regarding parabionts and chimeras as special cases of transplantation of whole or partial animals, I found that ex-parabionts accept subsequent skin exchanges only from the homologous ex-parabiont; reciprocal chimeras are compatible provided each animal portion contains a primary blood source, and will accept transplants as frogs only from the homologous recombinant. Chimeric recombinations made anterior to the heart field prove incompatible and fail to survive to maturity. Successful chimeras as well as ex-parabionts survive to maturity and are apparently normal in every antigen, radiation, and drugs.