Human corneal epithelial cell (HCEC) cultures were initiated from cadaver corneas kindly provided by the Illinois (Chicago, IL, USA) and Midwest Eye Banks (Ann Arbor, MI, USA). The 1.5-mm limbal rings were treated with Dispase (2 mg/mL; Gibco, Grand Island, NY, USA) at 37°C for 2 hours to separate the epithelial sheets, then digested in 0.25% trypsin-EDTA for 5 to 10 minutes. Cells were washed and resuspended in keratinocyte serum-free medium (KSFM; Invitrogen, Grand Island, NY, USA) and plated in collagen-coated tissue culture plates. Cells from passage 2 to 3 were used for experiments. In addition to primary corneal epithelial cells, human corneal-limbal epithelial (HCLE) cell line (telomerase-immortalized human corneal epithelial cell line kindly provided by Ilene Gipson, PhD) was used for some of the experiments. The HCLE cells were grown in KSFM.