Renal transplant recipients receiving loop diuretic therapy have increased urinary tract infection rate and altered medullary macrophage polarization marker expression.

Loop diuretics deplete the renal cortico-medullary salt gradient that has recently been established as a major modulator of immune responses. Renal transplant recipients suffer from a markedly increased rate of urinary tract infections (UTIs). Whether diuretic therapy affects renal macrophage polarization in the human kidney graft and the incidence of UTI have not been reported. In a cohort of 112 adult renal allograft recipients, loop diuretic therapy significantly correlated with the rate of UTI during five years after transplantation in uni- and multivariable regression analysis. The M1 macrophage marker human leukocyte antigen-DR (HLA-DR) and the M2 macrophage marker CD206 co-localized with the pan-macrophage marker CD68 in the kidney graft. Both were more common in renal medulla than cortex. With increasing loop diuretic dose, the renal medullary M1/M2 macrophage marker ratio decreased in early surveillance biopsies of this cohort. In vitro, the sodium chloride concentration dose-dependently increased monocyte chemotactic cytokine CCL2 production in human myeloid and renal tubular epithelial cells. More CCL2 was detected in the renal medulla than cortex of the kidney grafts. However, in patients receiving loop diuretic therapy, the renal cortico-medullary CCL2 gradient was diminished and CCL2 serum levels decreased significantly. Thus, diuretic therapy associated with increased bacteriuria and leukocyturia after kidney transplantation and a decreased M1/M2 macrophage marker ratio in the renal medulla. Hence, adjustment of diuretic therapy should be investigated further as a possible approach in patients with frequent UTIs.