The Action Of IL-12 Inducing T Lymphocyte Apoptosis And Effect On Graft-Versus-Host Disease.

Aim: IL-12 is an imunoregulatory cytokine that plays an essential role in cell-mediated immunity. This study was conducted to investigate: 1)Whether IL-12,in the absence or presence of an antigen,is able to induce T cell apoptosis and if so, 2)Which signal regulatory pathway /pathways utilizced by IL-12 is/are involved in this process, 3 )which apoptosis related molecules are involved in this process. 4)How does IL-12 modulate T cell apoptosis during antigen induces immune responses? 5)The relationship of IL-12 inducing T cell apoptosis and the changing in T cell subsets?Method: T cells,come from the healthy volunteer or the patients with CML underging bone marrow transplant at the day+14, +21, +60 were treated with various concentration of IL-12, apoptosis Was studied by Annexin V or TUNNEL assay, and surface molecules (CD25, CD95, FasL, TNFRl)Was studied by flow cytometry analysis; Following IL-12 and inhibitor stimulating, The cells stained by FITC-labeled FasL, PE labeled anti CD95, APC-labeled anti FasL. and FITC-labeled anti TNFR1 McAb. T cells,come from mixed lymphocyte culture or donor ,treated with IL-12(50ng/ml). Apoptosis was studied by TUNNEL assay. Expression of surface molecules and Changing of T cells Subsets was determined by flow cytometry . The titre of IFN-r and IL-4 were tested by EIISA assayResults: IL-12, in the absence or presence of allogeneic antigen(Raji B cell), induces T cells to undergo apoptosis. Expresoionof FasL and CD25 were up-regulated in T cells under IL-12 treatment, while Fas and TNR1 show little change .Semiquantitative RT-PCR demonstrated that IL-12 was able to up-regulate FasL mRNA expression. Caspase-3 inhibitor assay shows that apoptosis process needs the activation of Caspase-3. PTK inhibitor was able to suppress IL-12 induced T Cells apoptosis , in MLC system ,allogeneic B cells are able to induce T cells apoptosis, IL-12 up-regulate this process.IL-12 can stimulates FasL expression. The donor T cells also were induced to apoptosis by IL-12.the ratio of T cell subset CD4/CD8 were increased in this process, The titre of INF-r was increased but that of IL-4 was decreased.Conclusion: 1) IL-12 is able to induce apoptosis in T cells by a dose and time depent manner .2) IL-12 can increases CD25 expression on T cell surface, Which is an indicator for T cell activation and proliferation.3) IL-12 increases FasL expression on T cell but not CD95 or TNFR expression on T cell4) Caspase-3 inhibitor assay demonstrated the T cell apoptosied induced by LI-12 is mediated by Fas-FasL interaction and depend on activation of Caspase-35) PTK PKC and PKA were involved in the process of IL-12 inducing T cell apoptosis, The signaling pathways for activation or apoptosis of IL-12 might be the different.6) IL-12 enhances Th1 response and increases T cell subset CD4/CD8 proportion.