Production of high levels of Th1 and Th2 cytokines in mice with acquired transplantation tolerance.

Specific transplantation tolerance was induced in newborn mice by the intravenous injection of hematopoietic cells from semiallogeneic donors. Success of tolerance induction was tested by skin allografts. Spleen cells from mice bearing tolerated allografts for more than 60 days after transplantation spontaneously produced high levels of various cytokines. Production of both Th1 (IL-2, IFN-gamma) and Th2 (IL-4, IL-10) cytokines, as well as of IL-3, was significantly increased in tolerant animals. The elevated production of Th1 cytokines was associated with the high secretory activity of CD4+ cells, while the production of Th2 cytokines was high in both CD4+ and CD8+ cell populations. The hyperproduction of cytokines was an intrinsic property of the T cells from tolerant animals and was not caused by a larger size of major T-cell subsets. The production of high levels of cytokines was a consequence of neonatal induction of tolerance and persisted for a long time after skin grafting of neonatally tolerized animals. These results show that neonatal induction of transplantation tolerance results in the production of enhanced levels of Th1 and Th2 cytokines which could be involved in the establishment and maintenance of immunological tolerance.