The immunomodulatory and antitumor activities of trichosanthin-an abortifacient protein isolated from tian-hua-fen (Trichosanthes kirilowii).

Trichosanthin, a basic protein purified from the root tuber of Trichosanthes kirilowii, has been used effectively in China to induce midterm abortion in humans. In this paper, we show that trichosanthin at non-cytotoxic concentrations markedly inhibited the mitogen-induced lymphoproliferative response and the generation of a primary alloreactive CTL response in vitro. Similarly, the production of IL-2 by Con A activated splenocytes and the in vitro effector functions of macrophages were also significantly suppressed. In contrast, the cytolytic activity of CTL and NK cells was unimpaired. Moreover, the in vivo activation of NK cells was not significantly altered by a single injection of a non-toxic microgram amount of trichosanthin into mice. However, other immune reactivities such as the induction of a DTH response and the humoral antibody formation to SRBC were markedly depressed. Our data suggest that trichosanthin is a potent immunosuppressive protein that could affect humoral immunity and a variety of cell-mediated processes. In addition, our preliminary results show that this abortifacient protein could also inhibit the growth of a murine malignant tumour (MBL-2), both in vivo and in vitro.