Loss of tolerance to thymus-donor strain antigens in nude mice bearing long-term allogeneic thymus grafts.

In contrast to lymph node cells from nonthymus gland-implanted nude mice, which failed to respond to foreign alloantigens in mixed lymphocyte reaction tests, lymph node cells from nude mice implanted with either syngeneic or allogeneic thymuses responded well following stimulation with third-party allogeneic cells from strains unrelated to the nude host or thymus-donor strain. Responses to thymus-donor strain alloantigens by lymph node cells from nude mice implanted with allogeneic thymuses were in part dependent upon the duration of the thymic implants; no responses were observed using cells from mice implanted 3 mth previously whereas the majority of experiments yield positive responses using cells from mice implanted 12 mth previously, suggesting a functional breakdown of the tolerant state with time post allogeneic thymus implantation. In no case were positive responses specific for the nude host strain observed.