Abstract
Purpose: :
Inflammatory chemokines, activating the chemokine receptors CX3CR1, CCR1, CCR2 and CCR5, are implicated in trafficking, proliferation and activation of retinal microglial cells (MCs), which are potentially implicated in a variety of neurodegenerative and neovascular retinal diseases. We here studied, chemokine and chemokine receptor expression in the normal healthy retina.
Methods: :
Chemokine and their receptors expression was studied on healthy human retina by immunofluorescence and immunohistochemistry respectively. A total of seven eyes were used in this study. Eye donors were of an average age of 60 and had no known ophthalmic disorder. Retina was separated from choroid and post-fixed in cold acetone. CCR1, CCR2, CCR5 and CX3CR1 immunofluorescence was performed on retinal flatmounts. CCL2, CCL3, CCL5, and CX3CL1 immunohistochemistry was performed on paraffin sections.
Results: :
In human healthy retina CCR1, CCR2, CCR5 and CX3CR1 are expressed predominantly on CD18+ microglia. CX3CR1 is strongly expressed by all microglia. CCR1 and CCR5 expression is intermediate, while CCR2 is relatively weak. CX3CL1 (the ligand of CX3CR1) and CCL5 (a ligand of CCR1 and CCR5) are expressed throughout all layers of the retina and in the retinal pigmented epithelium (RPE). Intermediate to weak expression of CCL3 (a ligand of CCR1 and CCR5) in the inner layer of the retina and in the RPE was observed whereas CCL2 expression is restricted to blood vessels.
Conclusions: :
We show that chemokine receptors are expressed at different levels by microglia in the healthy retina and that CCL5 and CX3CL1 are constitutively expressed in normal human retina.
Keywords: microglia • cytokines/chemokines • retina