Purpose: To compare ocular surface cytokine expression in healthy controls and subjects with moderate dry eye and to study the ability of interleukin (IL)-1beta to modulate cytokine expression in cultured human conjunctival epithelial cells (CECs).
Methods: Subjective (symptom questionnaire) and objective (tear osmolality, fluorescein tear break-up time [TBUT]) measures of dry eye were determined in five healthy controls and five subjects with moderate dry eye. Tear clearance rates were measured with a fluorophotometer. Enzyme immunoassay and a cytokine bead assay were used to quantify IL-1beta in tear fluid. RT-PCR was performed to detect expression of IL-1beta, IL-6, IL-8, growth-related oncogene (GRO)-beta, intercellular adhesion molecule (ICAM)-1, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), and ephrin A5 in conjunctival impression cytology (CIC) samples and in CECs (IOBA-NHC cell line, n=3; primary cultured CEC, n=3) exposed to 10 ng/mL IL-1beta for 6 hours.
Results: Subjects with moderate dry eye had significantly higher symptom scores, higher tear osmolality, and shorter TBUT than healthy controls. Subjects with dry eye demonstrated slightly slower tear clearance (13.1% per minute) than healthy controls (15.4% per minute). Very low levels of IL-1beta protein were detected in the tear fluid of both groups. TRAIL was constitutively expressed in CIC samples, whereas IL-1beta, IL-6, and GRO-beta were absent. Weak expression of IL-8 (two healthy, four dry eye), ICAM-1 (four healthy, four dry eye), and ephrin A5 (one healthy, two dry eye) was observed. IL-1beta upregulated its own expression and that of IL-6, IL-8, GRO-beta, and ICAM-1 in cultured CECs but not that of ephrin A5 or TRAIL.
Conclusions: The lack of major differences in ocular surface cytokine expression between the two groups of subjects implies other inflammatory pathways or etiologies are involved in moderate dry eye. Although IL-1beta modulated the expression of various cytokines in cultured CECs, its absence in tear fluid and CIC samples suggests that IL-1beta does not play a modulatory role in moderate dry eye.