CD18 and ICAM-1-dependent corneal neovascularization and inflammation after limbal injury

Abstract

Extensive limbal injury is a leading cause of irreversible blindness. The destruction of corneal limbal stem cells often results in corneal neovascularization and an optically inferior epithelium. Previous work has shown that the neovascularization after limbal injury is vascular endothelial growth factor (VEGF)-dependent, with much of the VEGF emanating from the inflammatory cells that invade the cornea. Using a relevant mouse model of limbal injury, we examined the role of CD18 and intercellular adhesion molecule-1 (ICAM-1) in limbal injury-induced neovascularization. The results show that CD18- and ICAM-1-deficient mice developed 35% (n = 5, P = 0.003) and 36% (n = 5, P = 0.002) less neovascularization than strain-specific normal controls, respectively. The corneal neutrophil counts were similarly reduced by 51% (n = 5, P < 0.003) and 46% (n = 5, P < 0.006), respectively. When VEGF mRNA levels were analyzed, they were reduced by 66% (n = 3, P = 0.004) and 48% (n = 3, P = 0.024), respectively. Taken together, these data identify CD-18 and ICAM-1 as mediators of the inflammatory and VEGF-dependent corneal neovascularization that follows limbal injury. The targeting of CD18 and ICAM-1 may prove useful in the treatment of inflammation-associated neovascularization in the cornea and elsewhere.

Figure 1.

Examples of corneal neovascularization 7 days after epithelial debridement. The corneas come from a normal C57BL6J mouse (left), an ICAM-1-deficient mouse (middle), and a CD18-deficient mouse (right). Vessels were highlighted via intravenous injections of fluorescein-linked Lycopersicon esculentum lectin. KO, knockout. Original magnification, ×5.12; scale bar, 100 μm. Image size of 200 × 300 pixels is shown from the acquired image of 624 × 480 pixels.

Figure 2.

Percent area of corneal neovascularization 2, 4, and 7 days after epithelial debridement. The area of neovascularization is shown as the percent of total corneal area. KO, knockout. *, Denotes P < 0.05 versus other conditions at same time point.

Figure 3.

The total number of PMN in five standardized high-power fields from corneas 2, 4, and 7 days after epithelial debridement. KO, knockout. *, Denotes P < 0.05 versus other conditions at same time point.

Figure 4.

VEGF mRNA levels normalized to 18S mRNA, expressed in arbitrary densitometry units, from corneas harvested 2, 4, and 7 days after epithelial debridement. KO, knockout. *, Denotes P < 0.05 versus other conditions at same time point.