Recipient interleukin-1β production is critical for lung allograft acceptance

Proinflammatory cytokines, including IL-1β, TNF-α, and IL-6 have been linked to graft rejection and protocols have been developed to target these in solid organ transplant recipients. Pathways regulating rejection and tolerance differ across organs and remain poorly understood in lungs. Here, we used a mouse lung transplantation model to examine the role of inflammatory cytokines in graft acceptance. We found that recipient IL-1β drove systemic granulocyte colony-stimulating factor (G-CSF) release early after transplantation and promoted allograft infiltration with neutrophils that express immunosuppressive gene signatures. IL-1β promoted inducible nitric oxide synthase (iNOS) expression in neutrophils and accumulation of nitric oxide (NO) in allografts, a pathway that is critical for the acceptance of transplanted lungs. We observed that human and mouse neutrophils from lung transplant recipients suppress T cell responses in an NO-dependent fashion. Finally, recipients deficient in Il1b, but not Tnfa or Il6, acutely rejected lung allografts despite receiving immunosuppression that results in tolerance when administered to wildtype hosts. Thus, contrary to the widely held notion that proinflammatory cytokines promote deleterious outcomes after transplantation, our findings uncovered a previously unknown role for recipient IL-1β as a critical mediator of pulmonary allograft acceptance. Our findings inform future studies developing lung-specific immunosuppressive strategies.