The chemokine receptors CCR2 and CX3CR1 mediate monocyte/macrophage trafficking in kidney ischemia–reperfusion injury

Chemokines and their receptors such as CCR2 and CX3CR1 mediate leukocyte adhesion and migration into injured tissue. To further define mechanisms of monocyte trafficking during kidney injury we identified two groups of F4/80-positive cells (F4/80low and F4/80high) in the normal mouse kidney that phenotypically correspond to macrophages and dendritic cells, respectively. Following ischemia and 3 h of reperfusion, there was a large influx of F4/80low inflamed monocytes, but not dendritic cells, into the kidney. These monocytes produced TNF-α, IL-6, IL-1α and IL-12. Ischemic injury induced in CCR2−/− mice or in CCR2+/+ mice, made chimeric with CCR2−/− bone marrow, resulted in lower plasma creatinine levels and their kidneys had fewer infiltrated F4/80low macrophages compared to control mice. CX3CR1 expression contributed to monocyte recruitment into inflamed kidneys, as ischemic injury in CX3CR1−/− mice was reduced, with fewer F4/80low macrophages than controls. Monocytes transferred from CCR2+/+ or CX3CR1+/− mice migrated into reperfused kidneys better than monocytes from either CCR2−/− or CX3CR1−/− mice. Adoptive transfer of monocytes from CCR2+/+ mice, but not CCR2−/− mice, reversed the protective effect in CCR2−/− mice following ischemia-reperfusion. Egress of CD11b+Ly6Chigh monocytes from blood into inflamed kidneys was CCR2- and CX3CR1-dependent. Our study shows that inflamed monocyte migration, through CCR2- and CX3CR1-dependent mechanisms, plays a critical role in kidney injury following ischemia reperfusion.