Role of thymic- and graft-dependent mechanisms in tolerance induction to rat kidney transplant by donor PBMC infusion

In vitro Treg suppression assays

Determining the activity of a regulatory T-cell population in vitro is often the first step in analyzing its function. To obtain reliable and reproducible results, it is critical to follow the protocol that is most applicable to your experimental question. We have outlined below a basic in vitro suppression assay as well as a variety of alternative/additional protocols that can be utilized alone or in combination as desired.

The Toll-IL-1R member Tir8/SIGIRR negatively regulates adaptive immunity against kidney grafts

Members of the TLR/IL-1R superfamily mediate ischemia/reperfusion injury and initiate immune response in transplanted organs. In this study, we tested the hypothesis that Toll-IL-1R8 (TIR8), a negative regulator of TLR/IL-1R highly expressed in the kidney, modulates immune cell activation underlying kidney rejection. In a mouse model of fully mismatched kidney allotransplantation in which the graft is spontaneously accepted, intragraft Tir8 expression was enhanced compared with naive kidneys. Targeted deletion of Tir8 in the graft exerted a powerful antitolerogenic action leading to acute rejection. Similarly, in a mouse model of kidney graft acceptance induced by costimulation blockade, most Tir8(-/-) grafts were acutely rejected. Despite similar levels of TLR4, IL-1R, and their ligands, the posttransplant ischemia/reperfusion-induced inflammatory response was more severe in Tir8(-/-) than in Tir8(+/+) grafts and was followed by expansion and maturation of resident dendritic cell precursors. In vitro, Tir8(-/-) dendritic cell precursors acquired higher allostimulatory activity and released more IL-6 upon stimulation with a TLR4 ligand and TNF-alpha than Tir8(+/+) cells, which may explain the increased frequency of antidonor-reactive T cells and the block of regulatory T cell formation in recipients of a Tir8(-/-) kidney. Thus, TIR8 acts locally as a key regulator of allogeneic immune response in the kidney. Tir8 expression and/or signaling in donor tissue are envisaged as a novel target for control of innate immunity and amelioration of graft survival.

Regulatory T cell suppression is potentiated by target T cells in a cell contact, IL-35- and IL-10-dependent manner

Regulatory T cells (T(reg)) are believed to suppress conventional T cell (T(conv)) proliferation in vitro in a contact-dependent, cytokine-independent manner, based in part on experiments in which T(reg) and T(conv) are separated by a permeable membrane. We show that the production of IL-35, a novel inhibitory cytokine expressed by natural T(reg), increases substantially following contact with T(conv). Surprisingly, T(reg) were able to mediate potent suppression of T(conv) across a permeable membrane when placed in direct contact with T(conv) in the upper chamber of a Transwell plate. Suppression was IL-35 and IL-10 dependent, and T(conv) activation was required for maximal potentiation of T(reg) suppression. These data suggest that it is the induction of suppression, rather than the function of T(reg) that is obligatorily contact dependent.