Macrophages, dendritic cells, and kidney ischemia-reperfusion injury

Abstract

Dendritic cells and macrophages are critical early initiators of innate immunity in the kidney and orchestrate inflammation subsequent to ischemia-reperfusion injury. They are the most abundant leukocytes present in the kidney, and they represent a heterogeneous population of cells that are capable of inducing sterile inflammation after reperfusion directly through the production of proinflammatory cytokines and other soluble inflammatory mediators or indirectly through activation of effector T lymphocytes and natural killer T cells. In addition, recent studies have indicated that kidney and immune cell micro-RNAs control gene expression and have the ability to regulate the initial inflammatory response to injury. Although dendritic cells and macrophages contribute to both innate and adaptive immunity and to injury and repair, this review focuses on the initial innate response to kidney ischemia-reperfusion injury.

Figure 1. Heterogeneity of antigen presenting cells in the kidney

Kidney section of the outer medulla from C57BL/6 background CX3CR1⁺/GFP mouse. GFP is expressed mainly on monocyte/macrophages and dendritic cells (green). Sections were also stained for MCH class II (PE-tagged IA-positive cells). High magnification of images of the kidney medulla viewed under a Zeiss LSM-510 confocal microscope showed CX3CR1-GFP⁺ cells in green and PE-tagged IA⁺ cells in red identifying dendritic cells.

Figure 2. Flow cytometric analysis of intrarenal leukocytes populations in kidney kidney ischemia/reperfusion injury

Suspended kidney cells were stained and, by gating on the CD45⁺7AAD⁻ live leukocyte population, F4/80⁺ macrophages were detected by flow cytometry. The profile of macrophage influx into kidneys in comparison to other leukocytes (as determined by flow cytometric analysis) following ischemia-reperfusion injury is shown in the early (0.5-24 hrs) and late (48-148 hrs) phases of reperfusion. GR-1, neutrophils; B220, B cells; CD4 and CD8, T cells; F4/80, macrophages.

Figure 3. Trafficking of monocytes in mice following kidney ischemia/reperfusion injury

Bone marrow CD11b⁺Ly6C^high monocyte/monocyte precursor egress to the blood circulation is CCR2-dependent. (a) Some of the Ly6C^high monocytes lose their CCR2 and Ly6C expression and are further characterized as being CD62L⁻GR-1⁻CX3CR1^high. (b) These ‘resident monocytes’ migrate to normal non-inflamed tissue rapidly after they are released in the blood and differentiate into tissue dendritic cells (DCs), which are CD11b⁺CD11c⁺IA^high CD86⁺F4/80^high (c) On the other hand, some of the monocytes continue to express CCR2⁺ and Ly6C^high on the cell surface and are also CX3CR1^lowGR-1^intCD62L⁺. (d) These ‘inflammatory monocytes’ respond to the gradient of chemokines (e) released from kidneys following ischemia-reperfusion injury. In the injured tissue, the macrophages derived from ‘inflamed monocytes’ are characterized as being CD62L⁺Gr-1^intLy6C⁺F4/80^low. Infiltrating macrophages produce large amounts of pro-inflammatory cytokines, which are involved in tissue injury.

Figure 4. Dendritic cells are important in the pathogenesis of kidney IRI

(a) CD11c⁺GFP⁺ cells (arrows) in mouse kidney sections from CD11c-DTR/GFP mice (which express the human diphtheria toxin receptor (DTR) as a GFP fusion protein) were revealed immunohistochemically with GFP antibody (FITC fluorescence, green). Biologically inactive mutant DT had no effect on the number of GFP positive CD11c cells in the CD11c-DTR/GFP sham and IRI mouse kidneys. However there were significantly less GFP labeled cells in the sham and IRI kidneys of CD11c-DTR/GFP mice after administration of bioactive DT. Scale bar = 50 μM. (b) Plasma creatinine level was measured in wild-type (WT) and CD11c-DTR/GFP mice that received mutant (control) or bioactive DT (4 μg/g) 48 h prior to surgery. Values are mean ± SE; N=2-11; ***, P< 0.001. (c) H&E staining of kidneys from WT and CD11c-DTR/GFP mice reveals marked tubular injury in WT kidneys after IRI. Pretreatment with bioactive but not mutant DT prior to kidney IRI protected CD11c-DTR mouse kidneys from injury. Arrows indicate necrotic tubules. Scale bar = 100 μm. Data in (a) and (c) are representative of more than 3 experiments. Data from L. Li et al.