Adhesion molecule expression in a rat model of Staphylococcus aureus endophthalmitis

To determine whether Staphylococcus aureus and its components induce expression of E-selectin and intercellular adhesion molecule (ICAM)-1 in rat ocular tissues and on human endothelial cells in culture.

Experimental and control rat eyes were injected with 80 colony-forming units of viable S. aureus and lipopolysaccharide-free sterile saline (NS), respectively. Eyes were enucleated and immediately frozen. E-selectin and ICAM-1 expression were evaluated on frozen sections by using standard immunohistochemical techniques. Using an enzyme-linked immunoassay, in vitro expression of E-selectin and ICAM-1 was evaluated on macrovascular endothelial cells after stimulation with S. aureus and selected purified components.

In S. aureus-injected eyes, E-selectin and ICAM-1 expression peaked at six to 24 hours, decreased slightly at 24 and 48 hours, and further declined by 72 hours. However, in NS-injected eyes, peak levels of E-selectin and ICAM-1 were seen at 6 hours, after which expression declined in the areas in which an increase was previously observed. In in vitro assays, peptidoglycan (0.01 microg/ml) induced a fourfold increase in E-selectin (P < 0.0001) and a twofold increase in ICAM-1 (P < 0.002) expression. Ribitol teichoic acid (RTA) (1 microg/ml) induced a twofold increase in E-selectin (P < 0.0001) and a threefold increase in ICAM-1 (P < 0.0001) expression.

Eyes injected with S. aureus demonstrated a more intense and prolonged expression of both E-selectin and ICAM-1 than did eyes injected with NS. In addition, S. aureus components induced the in vitro expression of these adhesion molecules on macrovascular endothelial cells. The relevance of these findings to microvascular endothelial cells is yet to be determined.