Urinary immune cell phenotype of severe AKI in critically ill patients.

Purpose: Cellular mechanisms involved in human renal recovery after an episode of acute kidney injury (AKI) are understudied. We aim to characterize the urinary immune cell phenotype of patients with AKI and evaluate its ability to predict renal recovery.

Methods: A prospective study of critically ill patients with stage ≥ 2 AKI by KDIGO and sterile leukocyturia at admission was performed. Urine samples were collected fresh at day 0 and 2 and samples were analyzed by flow cytometry for different leukocytes. Patients were categorized in renal recovery or no-recovery groups.

Results: 28 patients were included, all with sepsis, 60.7% of which recovered renal function. The main urinary leukocytes present were neutrophils, followed by mononuclear phagocytic cells and B cells. Patients who recovered renal function had more M2 macrophages at day 2 (p = 0.043) and less B cells at admission (p = 0.006). M2 macrophages had an AUC-ROC of 0.796 (0.601-0.990) for recovery prediction and B cells an AUC-ROC of 0.743 (0.560-0.926) for no recovery. B regulatory cells were found in the urine of AKI patients.

Conclusions: The urinary immune cell phenotype of severe AKI patients was composed essentially of neutrophils, mononuclear phagocytic cells and B cells. Our data suggest that M2 macrophages may promote and B cells preclude renal recovery. More studies are needed to validate our results and further explore the role of immune cells in renal recovery.