Abstract
Purpose: :
LYVE-1 positive corneal lymphatics play a central role in ocular immunity. Lymphatic valves in the skin exhibit discontinuous LYVE-1 expression that might be due to smooth muscle cells recruitment. However, existence of valves in corneal lymphatics or discontinuous LYVE-1 expression have not been reported.
Methods: :
To characterize lymphatic phenotype, whole mount immunostaining with Abs for LYVE-1, CD31, αSMA, podoplanin, or FOXC2 was performed in corneas of C57BL/6 or BALB/c mice. To induce lymphangiogenesis, VEGF-A or FGF-2 pellets were implanted in the cornea (micropocket assay).
Results: :
Corneal lymphatics showed discontinuous LYVE-1 expression in areas that were CD31 positive. The number of the LYVE-1(-) CD31(+) lymphatic areas were significantly lower in BALB/c compared to C57BL/6 mice (0.5±0.2 vs. 7.8±1.2/cornea, n=10-11, P=0.00001). The LYVE-1(-) regions expressed podoplanin but not αSMA or FOXC2. The number of the LYVE-1(-) lymphatic regions in VEGF-A-implanted corneas did not significantly differ from untreated C57BL/6 mice. Interestingly, the number of LYVE-1(-) regions in FGF-2-implanted corneas was significantly fewer than in normal C57BL/6 (n=6-7, untreated, 7.5±0.8, FGF-2, 4.3±1.1, VEGF-A, 7.6±1.6/cornea, P=0.04 & 0.96, respectively).
Conclusions: :
Discontinuous LYVE-1 expression in lymphatic vessels in the cornea indicates phenotypic heterogeneity of lymphatic endothelial cells. The LYVE-1 negative endothelium does not represent classical signs of lymphatic valves. FGF-2-induced lymphanagiogenesis modulates LYVE-1 expression in the cornea.
Keywords: cornea: basic science • neovascularization