The mechanism of restriction of T-cell specificity by the genotype of the thymus in allogeneic and semiallogeneic chimeras was investigated. Lack of induction of delayed-type hypersensitivity (DTH) directed against antigen in association with the nonthymic parental haplotype in naive cells adoptively transferred into chimeras suggests the existence of an in vivo suppressive mechanism. However, it was not possible to suppress the expression of DTH in sensitized cells transferred into chimeras, or to transfer this suppression to normal naive recipients.

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