Abstract
Purpose: :
Microglial cells, monocytes and macrophages are cells from the monocytic cell lineage. Microglial cells and macrophages are implicated in a variety of neurodegenerative and neovascular retinal diseases. Inflammatory chemokines, activating the chemokine receptors CX3CR1, CCR1, CCR2 and CCR5, are implicated in trafficking, proliferation and activation of cells from the monocytic cell linage. The expression of the different inflammatory chemokine receptors in the retina and on retinal microglial cells (rMC) is unknown. We here analyzed the relative expression of CX3CR1, CCR1, CCR2 and CCR5 mRNA in whole retinal extracts, retinal microglial cells (rMC), and circulating blood monocytes (CBM).
Methods: :
Retina were dissected from PBS perfused 11week old C57Bl6 animals, trypsinized and MCs were purified by anti-CD11b magnetic sorting followed by flow cytometry (CD11bhigh/CD45low). CBMs were obtained from blood by gradient centrifugation and positive selection by adhesion properties in culture dishes. Chemokine receptors CCR1, CCR2, CCR5 and CX3CR1 mRNA expression were analyzed by qRT-PCR in these populations.
Results: :
CCR1, CCR5 and CX3CR1 mRNA were detectable in whole retinal extracts, 200fold enriched in rMCs and not detectable in rMCs depleted retinal extracts. CCR1 mRNA expression in rMCs was comparable to CBMs. In contrast, CX3CR1 mRNA and CCR5 mRNA expression were 1600-2000fold and 60fold increased in rMCs as compared to CBMs. CCR2 mRNA was undetectable in whole retinal extracts and rMCs but significantly expressed in CBMs.
Conclusions: :
rMCs are the main CX3CR1, CCR1 and CCR5 expressing cell type of the retina. While CCR1 expression in rMCs was comparable to CBMs, CX3CR1 and CCR5 mRNA were expressed at much higher levels in rMCs. CCR2 mRNA expression in health adults is extremely low. These results suggest that CBMs and rMCs react very differently to chemokine stimulation, at least at the beginning of an inflammatory response.
Keywords: inflammation • cytokines/chemokines • age-related macular degeneration