Objective：To explore the role of sublytic C5b -9 upregulating the transcription factor Krüppel -like factor 5（KLF5）in promoting the production of the inflammatory cytokine interleukin-23（IL-23）in glomerular mesangial cells（GMCs）of rats with Thy-1 nephritis（Thy-1N）. Methods：①A rat model of Thy-1N was established and rat GMCs were cultured in vitro. The expression levels of KLF5 and IL-23 in the renal tissues of Thy-1N rats and in GMCs stimulated by sublytic C5b-9 were detected by using Western blot （WB）. ②The levels of mRNA and protein of KLF5 and IL -23 in the GMCs transfected with either a KLF5 overexpressing plasmid （pIRES2 - KLF5）or a KLF5 small interfering plasmid（shKLF5）were examined by RT - qPCR and WB. ③The full - length IL - 23 promoter luciferase reporter gene plasmid（pGL3-IL-23-FL）was transfected into GMCs，followed by stimulation with sublytic C5b-9.Alternatively，pGL3- IL -23-FL was co -transfected with either pIRES2-KLF5 or shKLF5 into GMCs，and changes in IL -23 promoter activity were measured using a luciferase reporter gene assay. ④The LV-shKLF5 and LV-shCTR lentivirus vectors were respectively perfused into rat renal tissues via the artery perfusion. After confirming that LV - shCTR could enrich in rat kidney through animal imaging system and frozen section，the Thy-1N was reproduced，and the KLF5 and IL-23 expression in the renal tissues were measured by WB. Results：①The expressions of KLF5 and IL -23 were significantly increased in the renal tissues of Thy -1N rats and in GMCs stimulated by sublytic C5b-9，with KLF5 expression peaking slightly earlier than IL-23. ②Overexpression or knockdown of KLF5 in GMCs led to an increase or decrease in IL - 23 expression，respectively. ③ Sublytic C5b - 9 stimulation or KLF5 overexpression upregulated the activity of IL-23 promoter，while KLF5 knockdown markedly reduced the IL-23 promoter activity induced by sublytic C5b-9. ④IL-23 expression in the renal tissues of the rats treated by knocking down of renal KLF5 gene was significantly downregulated. Conclusion：In the early stage of Thy-1N in rats，sublytic C5b-9 stimulates GMCs to promote the transcription and expression of the IL-23 gene by upregulating KLF5.