Emergency granulopoiesis promotes neutrophil-dendritic cell encounters that prevent mouse lung allograft acceptance

The mechanisms by which innate immune signals regulate alloimmune responses remain poorly understood. In the present study, we show by intravital 2-photon microscopy direct interactions between graft-infiltrating neutrophils and donor CD11c⁺ dendritic cells (DCs) within orthotopic lung allografts immediately after reperfusion. Neutrophils isolated from the airways of lung transplantation recipients stimulate donor DCs in a contact-dependent fashion to augment their production of IL-12 and expand alloantigen-specific IFN-γ⁺ T cells. DC IL-12 expression is largely regulated by degranulation and induced by TNF-α associated with the neutrophil plasma membrane. Extended cold ischemic graft storage enhances G-CSF-mediated granulopoiesis and neutrophil graft infiltration, resulting in exacerbation of ischemia-reperfusion injury after lung transplantation. Ischemia reperfusion injury prevents immunosuppression- mediated acceptance of mouse lung allografts unless G-CSF-mediated granulopoiesis is inhibited. Our findings identify granulopoiesis-mediated augmentation of alloimmunity as a novel link between innate and adaptive immune responses after organ transplantation.