A peptide tetramer Tk‐tPN induces tolerance of cardiac allografting by conversion of type 1 to type 2 immune responses via the Toll‐like receptor 2 signal‐promoted activation of the MCP1 gene

Abstract

SummaryThe plant protein trichosanthin (Tk) and its derived peptide tetramer TktPN have been shown to stimulate the type 2 immune responses for treating autoimmune disease. This work explores the possibility of using Tk-tPN as a non-toxic immunosuppressant to induce transplantation tolerance using the mechanisms by which T-cell-mediated immune responses are transferred from type 1 to type 2 through innate immunity-related pathways. Immunocytes and cytokine secretions involved in the mouse cardiac allografting model with Tk-tPN treatment were characterized. Identification of critical genes and analysis of their functions through Toll-like receptor (TLR) -initiated signalling and the possible epigenetic changes were performed. Mean survival times of the cardiac allografts were delayed from 7Á7 AE 0Á3 days (control) to 22Á7 AE 3Á9 days (P < 0Á01) or 79Á1 AE 19Á2 days (P < 0Á0001) when Tk-tPN was introduced into the recipients alone or together with rapamycin, respectively. The grafting tolerance was donor-specific. The secretion pattern of the type 1 cytokine/ transcription factor (IL-2 + IFN-c + T-bet + ), which is responsible for the acute graft rejection, was shifted to the type 2 factor (IL-4 + IL-10 + Gata3 + ), together with a selective expansion of the IL-4/IL-10-producing CD8 + CD28 À regulatory T-cell subset. A TLR2-initiated high expression of chemokine gene MCP1 was detectable simultaneously. Epigenetically Tk/Tk-tPN could also acetylate the histone H3K9 of MCP1 promoter to skew the immunity towards T helper type 2 responses. Tk/ Tk-tPN is therefore capable of down-regulating the type 1 response-dominant rejection of cardiac allografts by evoking type 2 immunity through the activation of a TLR2-initiated signalling pathway and MCP1 gene to expand the IL-4/IL-10-secreting CD8 + CD28 À regulatory T cells. Tk-tPN could be a promising novel immunosuppressant to induce tolerance in allotransplantation.

Human CD8+CD28− T Suppressor Cells Expanded by IL-15 In Vitro Suppress in an Allospecific and Programmed Cell Death Protein 1-Dependent Manner

“…Although suppressive characteristic of CD8 + CD28 − Ts cells have been reported ( 19 , 20 , 24 ), there are other studies, which implies their cytotoxicity ( 31 ). In this study, we set up a CFSE-based assay as our previous report ( 24 ) and ruled out the cytotoxicity of CD8 + CD28 − Ts cells toward the priming APCs, which might contribute to the donor-specific suppression of proliferation.…”

“…One of the best characterized CD8 + Tregs populations is the CD8 + CD28 − T suppressor cells, which play a significant role in various diseases ( 16 – 18 ) including allogeneic transplantation ( 19 ). Human allospecific CD8 + CD28 − T cells have been generated in vitro when repeatedly stimulated with allogeneic antigen-presenting cells (APCs) for several rounds and has supplemental recombinant human IL-2 ( 20 ).…”

Trichosanthin induces anti-cancer effects by increasing the penetration of Granzyme B into tumor cells

“…Later studies demonstrated that DQ alleles play a critical role in TCS-induced immunosuppression by down-regulating function of CD8 cells [12] , and depletion of CD8 cells from total T cells or blocking expression of HLA-DQ molecules could effectively diminish TK's inhibitory activity against immune response [13] . Recently, Yang N et al reported that a TCS-derived peptide can suppress type 1 immune response by TLR2-dependent activation of CD8(+)CD28(-) tregs [14] , and suggest new eras in using TCS-tPN, a homo-tetramer, as a therapeutic reagent for Th1-dominant immunological diseases [14] and inducing tolerance of cardiac allografting [15] . And studies in major histocompatibility complex-mismatched mouse skin allograft also revealed the inspiring results of TCS effectively preventing allograft rejection, perhaps by reducing IL-2 and IFN-γ expression and inducing IL-4 and IL-10 expression [16] .…”