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F. Mackensen, C.A. Metea, J.T. Rosenbaum, S.R. Planck; The Immobility Of Iris Antigen Presenting Cells Is Not Explained By A Difference In Chemokine Receptor Or Ligand Profile . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5158.
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Chemokine receptors such as CCR7 and its ligands, CCL19 (ELC) and CCL21b (SLC), have been shown to be involved in maturation and homing of dendritic cells (DC) from peripheral sites to the lymph node. We previously could not detect migration of antigen–presenting cells from the iris to the regional lymph node. It is reasonable to think that differences exist between the eye and other non–lymphoid tissues as the eye is an immunoprivileged site. So we hypothesized that iris DCs might show a different CCR/ligand profile, i.e., lacking the ability to upregulate CCR7 upon stimulation, thus explaining the inability to migrate.
Eyes of 35 BALB/c mice were injected intravitreally with 2 µl of 250 ng E. coli lipopolysaccharide (LPS) or phosphate–buffered saline (PBS) and 5 mice served as naïve controls. After 3 and 6 hours, the iris–ciliary bodies were dissected. Tissues from groups of 5 eyes were pooled, total RNA was isolated and RT–PCR for chemokine receptor and ligand mRNA was performed. In addition, 1 eye from each of 3 animals was taken 6 hours after LPS injection for immunohistology (IHC). Spleen was used as positive control.
CCR5 mRNA was expressed in naïve iris, iris after PBS injection and after LPS injection in approximately equal levels. CCR6 mRNA was expressed in the spleen but was not detected in naïve iris, or after PBS or LPS injection. Equally no CCR7 mRNA expression was found in naïve iris, but it was weakly expressed in PBS–injected eyes and was approximately 3.4–fold upregulated after LPS injection. This was confirmed by IHC with no staining for CCR7 in control iris but positive staining in inflamed eyes. After LPS and PBS injection mRNA for the CCR7 ligands, CCL19 and CCL21b, was found, but not in naïve iris–ciliary bodies.
CCR7 mRNA levels are increased in inflamed iris–ciliary body. IHC confirms that CCR7 is expressed on DC–like cells in inflamed tissue, but not in naïve iris. Equally the mRNA of the ligands to CCR7 is only detectable in inflamed tissue. This finding is somewhat surprising, given the absence of lymphatic vessels inside the eye. The inability of iris DC to migrate might relate to the absence of co–factors, inhibitory substances, a lack of lymphatics, or sub–physiologic levels of chemotactic factors and ligands.
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