In terms of Th1/Th2 balance in response to signals given during donor antigen presentation, induction of tolerance is more often correlated with Th2-type than with Th1-type reactions. However, in our study, heart allograft survival was prolonged by treatment of rats with a Th2 inhibitor. Suplatast tosilate (IPD; Taiho; Tokyo, Japan) is a novel immunoregulator that suppresses IgE production and eosinophil infiltration through selective inhibition of interleukin (IL)-4 and IL-5 synthesis by Th2-like cells but not IFN-γ production in Th1 cells. Five LEW rats of DA heart grafts were treated with IPD (100 μg/day, p.o.) for 10 days. Heart allograft survival of all IPD-treated cases was prolonged more than 14 days while the beating of heart grafts in control groups was stopped within 9 days. In an in vitro study, the cell proliferation both in Con A blast and in mixed lymphocyte reaction assay was suppressed by IPD in dose-dependent manner. We could at least in part conclude that Th2 inhibition might temporarily suppress heart allograft rejection.
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