Activation of Liver-Resident DX5 Negative NK Cells after Intraportal Islet Transplantation Prevent the Engraftment of Secondary Transplanted Islets

Abstract

It has been recently reported that liver-resident DX5− natural killer (NK) cells have potent memory functions, which include differentiation into a long-lived memory subset and robust antigen-specific expansion to a secondary challenge. We have previously demonstrated that liver NK cells play a pivotal role in islet graft loss during the early phase after intraportal syngeneic islet transplantation (IT). In this study, we investigated the mechanism of liver-resident DX5− NK cells activation after IT and the influence of primary IT on the engraftment of secondarily transplanted islets. To evaluate the mechanism of NK cells activation early after IT, liver NK cells from C57BL/6 mice were cultured for 24 h in the presence of TNFα, IFNγ, and IL-1β, mimicking instant blood-mediated inflammatory reaction. Furthermore, we established a multiple IT model for evaluating the memory functions of NK cells in vivo; 400 islets were secondarily transplanted following primary IT with 200 islets. Surface molecules on liver NK cells were analyzed to evaluate the phenotypical and functional alteration of liver NK cells from the early to the late phase after IT. The population of DX5− NK cells significantly expanded 2.4 times compared to naive condition (p < 0.01) after the cytokine stimulation dominantly associated with TNFα, and the significant increase of both CD69 and CXCR3 expression on liver NK cells was observed (24 h/fresh ratio; 2.0, p < 0.01; 1.5, p < 0.01, respectively). In in vivo assay, the population of DX5− NK cells also promptly expanded and the expression of CD69, TRAIL, and CXCR3 on liver NK cells were significantly increased at 24 h after IT, meanwhile this phenomenon was restored by the administration of anti-TNFα antibody. At the late phase after IT, a significant and persistent increase of DX5− NK cells, expression of CD69, TRAIL, and CXCR3 on liver NK cells was observed compared to naive condition (35 d/0 d ratio; 2.2, p < 0.01, 2.3, p < 0.01, 3.7, p < 0.01, 2.0, p < 0.05, respectively). The syngeneic 400 islets of primary IT mostly achieved normoglycemia in diabetic mice, whereas the same mass of secondary IT failed to induce normoglycemia in the recipients received syngeneic 200 islets of primary IT. Our findings indicate that the liver-resident DX5− NK cells significantly and persistently expanded even after syngeneic IT, and those memory-like NK cells may target both of originally engrafted islets and even secondary transplanted islets.