Neutrophil extracellular trap fragments stimulate innate immune responses that prevent lung transplant tolerance

Abstract

Neutrophil extracellular traps (NETs) have been shown to worsen acute pulmonary injury including after lung transplantation. The breakdown of NETs by DNAse‐1 can help restore lung function, but whether there is an impact on allograft tolerance remains less clear. Using intravital 2‐photon microscopy, we analyzed the effects of DNAse‐1 on NETs in mouse orthotopic lung allografts damaged by ischemia‐reperfusion injury. Although DNAse‐1 treatment rapidly degrades intragraft NETs, the consequential release of NET fragments induces prolonged interactions between infiltrating CD4+ T cells and donor‐derived antigen presenting cells. DNAse‐1 generated NET fragments also promote human alveolar macrophage inflammatory cytokine production and prime dendritic cells for alloantigen‐specific CD4+ T cell proliferation through activating toll‐like receptor (TLR) — Myeloid Differentiation Primary Response 88 (MyD88) signaling pathways. Furthermore, and in contrast to allograft recipients with a deficiency in NET generation due to a neutrophil‐specific ablation of Protein Arginine Deiminase 4 (PAD4), DNAse‐1 administration to wild‐type recipients promotes the recognition of allo‐ and self‐antigens and prevents immunosuppression‐mediated lung allograft acceptance through a MyD88‐dependent pathway. Taken together, these data show that the rapid catalytic release of NET fragments promotes innate immune responses that prevent lung transplant tolerance.

Recombinant human ADAMTS13 treatment and anti-NET strategies enhance skin allograft survival in mice

“…In contrast to our findings that disruption of NETs increases skin allograft survival, Scozzi et al reported that the release of NET fragments by DNase 1 stimulates innate immune responses that prevent tolerance of the lung transplant . Such a discrepancy could be due to the difference in the type of organ that is transplanted.…”

“…The current study showed, for the first time, that NETs are generated in skin allografts in both mice and humans and contribute to allograft rejection. This corroborates the findings on orthotopic lung transplant, where NETs are present in the graft, and disruption of NETs improves primary graft function . We also showed that rhADAMTS13, which effectively dampens inflammatory responses post skin allograft transplant, profoundly enhances allograft longevity, as well.…”

“…This corroborates the findings on orthotopic lung transplant, where NETs are present in the graft, and disruption of NETs improves primary graft function. 21,22 We also showed that rhADAMTS13, which effectively dampens inflammatory responses post skin allograft transplant, profoundly enhances allograft longevity, as well. The exact mechanism through which rhADAMTS13 has this effect is not known, but it likely implicates the disruption of NET retention.…”

“…Such a discrepancy could be due to the difference in the type of organ that is transplanted. While alloimmune response to the skin allograft is attributed to the infiltration of T cells preactivated in the draining lymph node, T cell priming occurs in the allograft tissue of the lung transplant where NET fragments prolong the interaction between antigen‐presenting cells and T cells . To the general field of organ transplant, inhibiting NET generation, rather than cleaving NETs, may represent an unequivocal beneficial approach to enhance allograft survival and tolerance.…”

“…[18][19][20] Intriguingly, NETs were present in the lungs of mice subjected to orthotopic lung transplant and were at higher levels in the bronchoalveolar lavage fluid of patients with severe primary graft dysfunction after lung transplant compared to patients free of the dysfunction. 21 Disruption of NETs by DNase 1 rescued the function of the lung allografts in mice, 21,22 indicating a pathogenic role of NETs in allograft failure.…”