Abstract
Background and Aims
Acute kidney injury (AKI), even if followed by renal recovery, is a risk factor for the future development of chronic kidney disease (CKD) and end- stage renal disease. It has been postulated that interleukin-10 (IL-10)-producing Regulatory B cells (Breg) play an important role for the tissue repairment in several tissues and organs. Basically, protective role of Breg has been reported in inflammatory bowel disease. In the kidney, it has been shown that IL-10 suppresses renal function decline and improves renal prognosis in IRI model, a typical model of AKI. However, the identity of Breg in the kidney and their origin have not been clarified. Further, how the Breg works during the transition from AKI to CKD is not known. Therefore, first we investigated whether Breg existed in renal tissue on the progression from AKI to CKD in IRI model mice. Further, we performed splenectomy, and examined the renal injury, Breg, and plasma IL-10 levels in this model.
Method
To examine the existence of Breg in the kidney of IRI model, we used 8-10 weeks-old GFP / IL-10 mice based on C57BL / 6J mice. They are reporter mice for IL-10 producing cells, and can visualize IL-10 producing cells under a fluorescence microscope without fluorescent immunostaining. We prepared following three groups, sham, IRI (unilateral), and IRI + SN (splenectomy) groups. Mice were anesthetized with chloral hydrate (4 g/kg,, intraperitoneal). After making a midline incision, exposed a blood vessel of the left renal pedicles and clamped it for 30 min by clips. one day, 7 days, and 14 days after the surgery, mice were sacrificed, and renal function and plasma IL-10 levels as well as tissue damages by PAS and Masson’s Trichrome staining were assessed. Tissue IL-10-producing cells were detected by flow cytometry.
Results
There was no difference of plasma IL-10 levels and renal tubulointerstitial injury in IRI group and IRI+SN group on day 1 after IRI. However, on day 7 and day 14, plasma IL-10 levels became gradually higher in IRI group, and SN decreased the increase in IL-10 levels. Tubulointerstitial injury was induced by IRI and SN further worsened tubular damages. Serum Cr and BUN levels were not different in three groups due to normal right kidney. On day 1, number of IL-10-producing B cells increased in the spleen and renal medulla in IRI group confirmed by flow cytometry, which was completely diminished by SN, suggesting that origin of the infiltrated Breg might be spleen, thereby being involved in the protective role in IRI injury in the kidney.
Conclusion
We report for the first time that Breg might be recruited from spleen by AKI, which may be one of the mechanisms to prevent the progression to CKD.
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