Objective:To investigate the role of immunoglobulin-like domain-containing receptor 2 (Ildr2) in renal fibrosis induced by ischemia-reperfusion.Methods:Ildr2 knockout mice (KO group) were constructed using CRISPR/Cas9 technology, and wild-type mice were as the control group (WT group). The unilateral renal ischemia-reperfusion (UIR) model (UIR group) was constructed by clamping the left renal pedicle, and was divided into KO-UIR group and WT-UIR group after modeling. Sham operation mice (sham group) were not treated with ischemia. Serum creatinine was measured by creatinine oxidase method. Blood urea nitrogen was detected by the diacetyloxime colorimetric method. The urinary albumin level was measured by enzyme-linked immunosorbent assay, and urinary albumin/creatinine ratio was calculated. HE, PAS and MASSON staining were used to detect the infiltration of inflammatory cells and the degree of fibrosis in renal tissues. The mRNA expression levels of Ildr2, kidney injury-associated molecules neutrophil gelatinase-associated lipocalin ( NGAL) and kidney injury molecule-1 ( KIM-1), fibrosis markers typeⅠcollagen α 1 ( Col1α1), fibronectin 1 ( Fn1), α-smooth muscle actin ( α-SMA) and connective tissue growth factor ( CTGF), as well as inflammation-related molecules macrophage marker F4/80 and monocyte chemoattractant protein-1 ( MCP-1) were detected by real time quantitative PCR (qRT-PCR). The protein levels of Ildr2, α-SMA and Col1α1 were detected by immunofluorescence and Western blotting. Results:(1) qRT-PCR and Western blotting showed that the expression levels of Ildr2 mRNA and protein in UIR group were significantly lower than those in sham group (both P<0.05). (2) There were no significant differences in body weight, serum creatinine, blood urea nitrogen, total cholesterol, low density lipoprotein, high density lipoprotein and triglyceride between KO group and WT group (all P>0.05). qRT-PCR results showed that there were no significant differences in the mRNA expression levels of NGAL, KIM-1, α-SMA, Col1α1, CTGF, Fn1, MCP-1 and F4/80 between KO group and WT group (all P>0.05). Histological staining showed no abnormal inflammatory cell infiltration and interstitial fibrosis between KO group and WT group. (3) Compared with the WT-UIR group, serum creatinine and blood urea nitrogen in the KO-UIR group were significantly higher (both P<0.05). qRT-PCR results showed that the mRNA expression levels of NGAL, F4/80, MCP-1, Col1α1, α-SMA, and CTGF in the KO-UIR group were significantly higher than those in the WT-UIR group (all P<0.05). Immunofluorescence and Western blotting results also showed that the protein expression levels of Col1α1 and α-SMA in the KO-UIR group were significantly higher than those in the WT-UIR group (all P<0.05). Histological staining showed that, compare with WT-UIR group, KO-UIR group had more severe inflammatory infiltration and more collagen fiber deposition. Conclusion:Ildr2 knockout does not cause phenotypic changes in mice under normal physiological conditions. Ildr2 plays a regulatory role in UIR injury, and Ildr2 deletion aggravates the degree of renal fibrosis induced by UIR.