Abstract
Purpose: :
Previous work has shown that human corneal epithelial cells (HCECs) produce surfactant protein D (SP–D), that this protein is up–regulated by cells in response to Pseudomonas aeruginosa challenge, and that SP–D inhibits P. aeruginosa invasion of epithelial cells. This study tested the hypothesis that hypoxia and contact lens exposure suppress the up–regulation of SP–D by HCECs in response to P. aeruginosa infection.
Methods: :
HCECs were grown in one of four conditions: hypoxia (5% O2, 5% CO2, 90% N2), with low oxygen transmissible contact lenses (low Dk), with high oxygen transmissible contact lenses (high Dk), or control conditions (20% O2, 5% CO2) for five days. HCECs were starved in serum–free media for 24 hours and then exposed to a heat–killed, invasive strain of P. aeruginosa, PAK,for 14 hours. Intracellular levels of SP–D were analyzed by Western blot or immunohistochemistry.
Results: :
Western blot analysis showed that hypoxia alone does not affect intracellular SP–D levels compared to levels in cells grown in standard conditions. However, when cells grown in hypoxia were challenged with P. aeruginosa, intracellular up–regulation of SP–D as detected by Western blot was increased compared to the up–regulation seen in controls. Immunohistochemistry qualitatively showed that exposure to low or high DK lenses in the absence of bacterial challenge does not affect SP–D levels compared to cells not grown with contact lenses. When infected with P. aeruginosa, immunohistochemistry showed that low and high DK lenses suppressed SP–D up–regulation compared to controls.
Conclusions: :
Neither hypoxia nor contact lens exposure affect SP–D levels by corneal epithelial cells in the absence of P. aeruginosa challenge. However, when cells are exposed to the bacteria, hypoxia increases SP–D up–regulation while both low and high DK lenses decrease SP–D up–regulation. This suggests that hypoxia and contact lenses affect the cornea's ability to respond to bacterial infection, with hypoxia making the cells more responsive. The hypoxic effects previously shown to be associated with contact lenses are perhaps offset by the mechanical or stagnation effects contact lenses have on corneal cells.
Keywords: cornea: epithelium • microbial pathogenesis: experimental studies • contact lens