Abstract
Purpose::
Dendritic cells reside in virtually all organs and perform crucial regulatory functions in immunity. In the eye, they have been detected by histology and immunohistochemistry in cornea, iris, ciliary body, and choroid of different species. The aim of the present study was to visualize these cells in a living organism by observing them ophthalmoscopically in the fundus of experimental mice.
Methods::
We have used heterozygous CX3CR1-GFP knock-in mice, in which tissue dendritic cells (DC) and blood monocytes (the DC precursors) are constitutively fluorescent due to expression of green fluorescent protein (GFP) under the control of fractalkine receptor promoter. The mice were examined by a confocal scanning laser ophthalmoscope (HRA II, Heidelberg Engineering, Dossenheim, Germany) in the autofluorescence (AF) mode. For excitation an argon laser (488 nm) was used (barrier filter 500 nm). This mode is usually employed to visualize lipofuscin accumulation on the level of the retinal pigment epithelium of humans. It closely matches the fluorescence requirements of GFP. To enhance the AF signal, a mean of up to 20 single images was calculated. Wildtype C57/BL6 mice served as controls.
Results::
Heterocygous CX3CR1-GFP knock-in mice displayed a dense network of fluorescent cells with the morphology of DC. These cells were evenly distributed without any relationship to retinal or choroidal vessels. No fluorescent cells were found in the fundus of wildtyp control mice.
Conclusions::
The system presented here is the first to allow in vivo visualization of dendritic cells in the fundus. It is expected to be a helpful adjunct in further studies on the physiological and pathological role of dendritic cells in the posterior eye segment.
Keywords: imaging/image analysis: non-clinical • immunomodulation/immunoregulation