Blockade or deficiency of PD-L1 expression in intestinal allograft accelerates graft tissue injury in mice

The importance of PD-1/PD-L1 interaction to alloimmune response is unknown in intestinal transplantation. We tested whether PD-L1 regulates allograft tissue injury in murine intestinal transplantation. PD-L1 expression was observed on the endothelium and immune cells in the intestinal allograft. Monoclonal antibody treatment against PD-L1 led to accelerated allograft tissue damage, characterized by severe cellular infiltrations, massive destruction of villi, and increased crypt apoptosis in the graft. Interestingly, PD-L1^-/- allografts were more severely rejected than wild-type allografts, but the presence or absence of PD-L1 in recipients did not affect the degree of allograft injury. PD-L1^-/- allografts showed increased infiltrating Ly6G⁺ and CD11b⁺ cells in lamina propria on day 4, whereas the degree of CD4⁺ or CD8⁺ T cell infiltration was comparable to wild-type allografts. Gene expression analysis revealed that PD-L1^-/- allografts had increased mRNA expressions of Cxcr2, S100a8/9, Nox1, IL1rL1, IL1r2, and Nos2 in the lamina propria cells on day 4. Taken together, study results suggest that PD-L1 expression in the intestinal allograft, but not in the recipient, plays a critical role in mitigating allograft tissue damage in the early phase after transplantation. The PD-1/PD-L1 interaction may contribute to immune regulation of the intestinal allograft via the innate immune system.