*Purpose: Inflammatory macrophages contribute to the development of ischemia-reperfusion injury (IRI) and allograft rejection. However, the underlying mechanisms by which macrophage mediate allograft injury and repair remain unclear. IRE1a, a key component of the endoplasmic reticulum (ER) stress response, emerges as a critical regulator of innate immunity. This study aims to determine the role of macrophage-specific IRE1a in kidney transplant IRI and rejection.

*Methods: CD45.1 BALB/c kidneys were subjected to 4hr cold ischemia time (CIT) prior to transplanting into bi-nephrectomized macrophage-specific IRE1α knockout CD45.2 B6 mice (KO) or their wildtype littermates (WT). Graft survival and renal function were monitored until death or post-operative day (POD) 120. A multicolor flow cytometry was performed to phenotype graft-infiltrating cells. RNAseq were used to analyze gene profiles of sorted graft-infiltrating macrophages from WT or KO recipients.

*Results: Compared to WT allografts, KO allografts had significantly improved function as indicated by reduced levels of creatinine and BUN, along with less intensive acute tubular necrosis and decreased early mortality rate. The enhanced recovery of transplant IRI seen in KO allografts corresponded to the prolonged renal allograft survival and reduced Interstitial fibrosis at POD120. Further, the phenotypical analysis of graft-infiltrating cells showed that lack of IRE1a did not impair the early migration capacity of monocyte/macrophages to renal allografts during IRI, as the comparable numbers of monocyte/macrophages were detected in both WT and KO allografts at day 2. However, the RNA seq analysis revealed that IRE1a regulated the oxidative stress, immune responses, and macrophage/DC phenotypical shift pathways in graft-infiltrating macrophages. The data showed that deficiency of IREa downregulated the expression of pro-inflammatory M1-type genes (IFN-γ, HMGB1, and Myd88) and upregulated the anti-inflammatory M2-type genes (CD163, CD209, and Egf), linking to the enhanced resolution of sterile inflammation during renal allograft injury.

*Conclusions: These findings suggest that IRE1a deficiency ameliorated kidney transplant IRI and protected kidney allograft from rejection, likely through a mechanism that involves reprogramming graft-infiltrating macrophages toward an anti-inflammatory M2-type phenotype.

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