In strain combinations involving multiple non-H-2 disparities, neonatal skin grafts may survive significantly longer than adult grafts of similar genotype on normal adult hosts, and repeatedly outlive grafts of adult origin on immunosuppressed recipients. Moreover, newborn grafts of long-standing may render their hosts unresponsive to adult skin grafts from the same donor strain. With some H-2-compatible strain combinations in which homozygous neonatal grafts are rejected, F1 hybrid (heterozygous) grafts of similar age not only may survive indefinitely, but also may induce tolerance of subsequent adult parental strain homografts. These tolerogenic and gene dosage effects, although much weaker, can likewise be revealed with H-2-incompatible neonatal skin grafts.

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