Abstract
We developed an experimental set up that enables longitudinal studies of immune cell behavior in situ in the challenged as well as unchallenged kidney of anesthetized mice over several hours. Using highly controlled vacuum to stabilize the kidney, the superficial renal cortex could continuously be visualized with minimal disruption of the local microenvironment. No visible changes in blood flow or neutrophils and macrophages numbers were observed after several hours of visualizing the unchallenged kidney, indicating a stable tissue preparation without apparent tissue damage. Applying this set up to monocyte/macrophage (CX3CR1GFP/+) reporter mice, we observed the extensive network of stellate-shaped CX3CR1 positive cells (previously identified as renal mononuclear phagocytes). The extended dendrites of the CX3CR1 positive cells were found to bridge multiple capillaries and tubules and were constantly moving. Light induced sterile tissue injury resulted in rapid neutrophil accumulation to the site of injury. Similarly, microinfusion of uropathogenic Escherichia coli into a single nephron induced a rapid and massive recruitment of neutrophils to the site of infection, in addition to active bacterial clearance by neutrophils. In contrast, the kidney resident mononuclear phagocytes were observed to not increase in numbers or migrate toward the site of injury or infection. In conclusion, this model allows for longitudinal imaging of responses to localized kidney challenges in the mouse.
Highlights
The host immune response to injury and infections is both site- and situation-dependent, and is even influenced by the circadian rhythm, with variations in the mechanisms of leukocyte recruitment to different organs as well as to different infectious agents [1,2,3]
We describe an experimental set up that enables studies of immune cell behavior in the cortex of the mouse kidney, including transgenic animals, in both healthy animals and during injury and local bacterial infection in single nephron over several hours
Administration of anti-mouse Ly-6G antibodies intravenously revealed the presence of neutrophils interacting with capillary endothelium (Figure 2 and Supplementary Video 3), demonstrating that in our setting neutrophils normally scan the vasculature of the renal cortex in the unchallenged kidney
Summary
The host immune response to injury and infections is both site- and situation-dependent, and is even influenced by the circadian rhythm, with variations in the mechanisms of leukocyte recruitment to different organs as well as to different infectious agents [1,2,3]. Tissue resident immune cells acting as sentinels, rapidly detect changes of the microenvironment, and respond This response includes macrophage phagocytosis and killing of the pathogens, and production of chemokines and cytokines to activate and recruit other immune cells to the site. The first cells to be recruited from circulation to the site of infections are neutrophils, which are competent bacteria-killers via the production of reactive oxygen species and antibacterial products. In addition to their role in host defense, leukocytes contribution to tissue restoration following injury has recently been recognized [4,5,6].
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