Support grant for Dr. Stephen Chiu: 2016 ASTS Resident Scientist Scholarship

Primary graft dysfunction (PGD) occurs in up to 50% of lung recipients and is the principal risk factor for acute graft loss and chronic lung allograft rejection. Neutrophil infiltration into the allograft has been shown to mediate PGD. However, mechanisms of neutrophil infiltration remain incompletely characterized. In a murine lung transplant model, we found that CX3CR1hi Ly6Clow non-classical monocytes remain attached to the pulmonary endothelium despite flushing with standard preservatives and are, therefore, transplanted with the donor lung. Elimination of these monocytes in the donor resulted significant protection from neutrophil infiltration of the allograft and abrogated physiologic signs of primary dysfunction. CD14lowCD16+ monocytes in humans are analogous to murine Ly6Clow monocytes, making these findings applicable to human lung transplantation. In additional preliminary experiments, we have found that knockout of CX3CR1 and Toll-like receptor (TLR) signaling in donor Ly6Clow monocytes also protected against infiltration of the allograft by neutrophils. Therefore, we hypothesize that CX3CR1 is necessary for attachment of Ly6Clow monocytes to the pulmonary endothelium and that TLR signaling is responsible for their activation during transplantation. In order to investigate this hypothesis, I propose to utilize core and innovative experiments in immunology, including adoptive transfer, flow cytometry, intravital multiphoton microscopy, cell culture, and live cell imaging techniques in a multidisciplinary collaborative training environment. Through the experiments outlined here, we hope to gain insight into the role of Ly6Clow monocytes as endothelial gatekeepers and mediators of neutrophil extravasation during PGD.