Tolerance induced by grafting semi-allogeneic adult skin to larval Xenopus laevis: Possible involvement of specific suppressor cell activity

Major histocompatibility complex (MHC)-homozygous Xenopus laevis were rendered tolerant to semi-allogeneic antigens by grafting skins of adult frogs during larval stages (larvally induced tolerance), and this tolerant state was compared with the tolerance induced in early thymectomized frogs by the grafting of semi-allogeneic nonlymphoid thymuses (thymus-reconstituted tolerance). In contrast to a total inability of thymus-reconstituted frogs both to reject skins and to exhibit a mixed leukocyte reaction (MLR) against the semi-allogeneic donor, larvally induced tolerant frogs showed a strong MLR against leukocytes of the tolerizing skin donor (split tolerance). Breakdown of the tolerant state in thymus-reconstituted frogs were easily accomplished by inoculation with syngeneic splenocytes, but this breakdown was extremely difficult to achieve in frogs with larvally induced tolerance. The injection of splenocytes from larvally induced tolerant frogs into normal frogs significantly suppressed semi-allogeneic graft rejection in the latter group; no suppression was obtained when splenocytes from thymus-reconstituted frogs were used. In addition, in the thymectomized frogs, recovery of allograft rejection capacity against the pertinent semi-allogeneic antigens were suppressed by the injection of splenocytes from larvally induced tolerant frogs, with the degree of suppression depending on the splenocyte dose. These results indicate that the larvally induced tolerant state is maintained by specifically induced suppressor cells affecting the in vivo allograft response but not the MLR.     

Characterization of a human ''midisatellite'' sequence.

We have examined the structure and DNA sequence of a human genomic locus that consists of a large hypervariable region made up of repeats of a simple sequence. With several restriction enzymes, the locus shows many restriction fragments that vary quantitatively as well as qualitatively. Other restriction enzymes produce only a single, high-molecular-weight fragment at this locus. Almost all of the fragments are revealed with a simple sequence probe. Southern transfers of the high-molecular-weight restriction fragments produced by the restriction enzymes NotI and SfiI, resolved by pulsed-field gel electrophoresis, gave at most two fragments, demonstrated to be allelic, showing that the majority of the restriction fragments seen in the complex patterns are at a single locus. The estimated size of the region homologous to the probe varied from 250 to 500 kilobases. DNA sequencing indicated that the region consists of tandem repeats of a 40-base-pair sequence. Some homology was detected to the tandem repeating units of the insulin gene and the zetaglobin pseudogene hypervariable regions, and to the "minisatellite" DNA at the myoglobin locus.