Acute phase liver graft injury significantly mobilized circulating endothelial progenitor cells, myeloid-derived suppressor cells and regulatory T cells

Abstract

OBJECTIVE: We aim to investigate the role of acute phase liver graft injury in mobilization of circulating endothelial progenitor cells (EPCs), myeloidderived suppressor cells (MDSCs) and regulatory T cells (Tregs) in a rat liver transplantation model and to explore the underlying mechanism. MATERIALS AND METHODS: A rat orthotopic liver transplantation model using the recipient with liver cirrhosis was established with the application of whole graft or small-for-size (50%) graft. Circulating EPCs, MDSCs and Tregs were detected by flow cytometry at day 1, 3 and 5 after transplantation. Intragraft mRNA levels of CXCR4 (acute phase inflammation and stem cell homing) and Tie2 (angiogenesis) were compared by qRT-PCR. Tregs (FOXP3+) accumulation in the grafts was detected by immunostaining. Intragraft infiltration of circulating cells (EPCs) from recipient source was further confirmed using the recipient rat with green fluorescence protein (GFP) labeling. RESULTS: There were more circulating EPCs (day 3: 1220 vs 550/105PBMC, p=0.032; day 5: 1064 vs 633/105PBMC, p=0.046) and MDSCs (day 3: 875 vs 220/105WBC, p=0.038; day 5: 358 vs 106/105WBC, p=0.043) at day 3 and 5, and more Tregs at day 5 (2604 vs 1414/105WBC, p=0.037) after transplantation using the small-for-size graft compared to whole graft. The intragraft CXCR4 and Tie2 mRNA levels were signifi cantly higher (CXCR4: 1.99 folds of whole graft, p=0.0064; Tie2: 2.01 folds of whole graft, p=0.019) in the small-for-size graft at day 3 after transplantation. There were more Tregs and inflammatory cells infiltration, and severer eosinophilic degeneration in the small-for-size graft. Intragraft infiltration of the circulating cells from the recipient source was confi rmed by detection of GFP positive signals in the graft. Involvement of angiogensis by recipient source EPCs was indicated by the detection of GFP+CD31+ and GFP+vW factor+ cells in the grafts. CONCLUSION: Acute phase small-for-size liver graft injury may play an important role in mobilization of circulating EPCs, MDSCs and Tregs through up-regulation of CXCR4 signaling. Higher population of circulating EPCs may contribute to intragraft new vessel formation, leading to angiogenesis and tumor recurrence. More MDSCs and Tregs mobilized to the circulating blood may cause tumor escape from the immune system.