Normal and isoimmune C3H and C57BL spleen cells were transferred intravenously into normal and irradiated allogeneic recipients and the fate of the donor cells determined by differential cytotoxicity and radioautographic techniques. It was found that spleen cells sensitized against their prospective recipients could be identified in the host's spleen for 1 day, whereas normal donor cells survived 2 to 3 days. Spleen cells presensitized with an indifferent antigen had survival times similar to normal donor cells. Irradiation of the recipients prior to cell transfer eliminated any difference in survival times between normal and presensitized donor cells in allogeneic hosts. It is concluded that the host plays an important role in the rapid destruction of spleen cells presensitized against host antigens.

Experiments in which sensitized and normal C57BL spleen cells were mixed and transferred into normal C3H mice indicated that as little as 5 to 10 per cent of the donor cell population need be sensitized for the entire mixture to behave as if it were obtained from a sensitized animal, as shown by its elimination in the 1-day interval.

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