Constitutive and inflammatory mediator-regulated fractalkine expression in human ocular tissues and cultured cells

Fractalkine (FKN) is a dual-adhesion molecule-chemokine that plays a role in inflammation but has not been explored in the eye. In the current study, constitutive expression of FKN was identified in human iris and retina, and its regulation by various cytokines in endothelial cells (ECs) and stromal cells from human iris, retina, and choroid was investigated.

Human iris and retina explants were evaluated for FKN mRNA and protein expression using RT-PCR and immunohistochemistry, respectively. Cultured ocular ECs and stromal cells were stimulated with various inflammatory mediators (endotoxin; TNFalpha; interferon-gamma; interleukin (IL)-1alpha, -4, -10, -13, -17, and -18; and/or CD40 ligand, or combinations thereof), with FKN mRNA being subsequently evaluated by cDNA array and/or RT-PCR and FKN protein by enzyme-linked immunoculture assay (ELICA) and/or by Western blot analysis.

Iris and retina explants constitutively expressed FKN protein in microvascular ECs and also in several stromal cell types. Iris and retina both express FKN mRNA. TNFalpha upregulated FKN in iris explants. All ocular microvascular ECs and stromal cultures expressed low FKN mRNA and/or protein levels, which were variably upregulated by endotoxin, TNFalpha, interferon-gamma, IL-1alpha, and/or CD40 ligand, but not by IL-18. In ECs, the Th2 cytokines IL-4 and -13, but not IL-10, reduced TNFalpha-induced FKN protein. IL-17, usually considered proinflammatory, reduced TNFalpha-induced FKN protein in ocular ECs.

FKN is expressed in various ocular tissues and cells. Inflammatory mediator modulation of ocular FKN expression suggests that this adhesive chemokine may play important roles in regulating leukocyte efflux in inflammatory eye diseases, such as anterior uveitis and retinochoroiditis.