We studied the alloreactive properties of donor T cells obtained from F1 mice that had recovered from the allosuppression of acute graft-vs.-host disease (GVHD) and showed mild symptoms of chronic GVHD, i.e., so-called secondary chronic GVHD. To this end, we used (B10 x DBA/2)F1 mice that had been injected with 10(8) B10 spleen cells 100-150 d previously. Such GVHD F1 mice were repopulated by lympho-hematopoietic cells of donor (B10) origin, which exhibited split tolerance towards the host: Whereas F1-specific donor T helper (Th) cells as well as T cells proliferating in the mixed lymphocyte reaction were readily demonstrable, F1-specific T suppressor (Ts) and T killer (Tk) cells were not, or were hardly, detectable; responses against third-party alloantigens were normal. Upon adoptive transfer to nonirradiated secondary recipients, the B10 cells obtained from the repopulated GVH F1 mice induced F1-specific enlargement of the draining popliteal lymph node and enhancement of the IgG formation therein. B10 cells of the same kind were unable, however, to induce lethal GVHD upon transfer to 950 rad-irradiated secondary (B10 x DBA/2)F1 recipients. We conclude that alloactivated donor Ts/Tk cells disappear from the host at a relatively early stage of GVHD, i.e., at the end of acute GVHD , presumably because they are short-lived. By contrast, the longevity of alloactivated donor Th cells causes the symptoms of secondary chronic GVHD.

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