Joining adult DBA/2J (H-2d) mice with adult (DBA/2J × C3H/HeJ)F1 (H-2d/H-2k) mice in parabiosis results in long-term survival of 44% of such pairs, the complete takeover of the F1 lymphoid and erythropoietic systems by parent type cells, and specific unresponsiveness toward C3H/HeJ skin grafts on the parental partner. In an adoptive transfer system measuring the killing of an 131I-iododeoxyuridine-labeled tumor that is H-2 compatible with C3H/HeJ, parabiont spleen cells show full reactivity upon sensitization to C3H/HeJ alloantigens and do not inhibit the sensitization of normal DBA/2J cells to C3H/HeJ. The adoptively transferred parabiont cells do not appear to be active unless reexposed to C3H/HeJ antigen. However, intact parabionts show accelerated tumor destruction in situ even when not deliberately restimulated with C3H/HeJ spleen cells. Parabiont serum gives accelerated tumor clearance on passive transfer. Parabiont serum also shows complement-dependent antibody titers in vitro of 1:10 to 1:20 against lymphoid target cell antigens coded for by genes in the interval from K to I-E of the H-2 complex. Most of this activity is sensitive to 2-mercaptoethanol. Although circulating antibody is present in the parabionts, F1 parabiont skin shows no delay in rejection by normal DBA/2J recipients.

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This work was supported by the Medical Research Council of Canada.

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