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Conjunctival Cytokine Expression in Symptomatic Moderate Dry Eye Subjects

From the College of Optometry, University of Houston, Houston, Texas.

PURPOSE. To compare ocular surface cytokine expression in healthy controls and subjects with moderate dry eye and to study the ability of interleukin (IL)-1ß 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-1ß in tear fluid. RT-PCR was performed to detect expression of IL-1ß, IL-6, IL-8, growth-related oncogene (GRO)-ß, 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-1ß 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-1ß protein were detected in the tear fluid of both groups. TRAIL was constitutively expressed in CIC samples, whereas IL-1ß, IL-6, and GRO-ß 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-1ß upregulated its own expression and that of IL-6, IL-8, GRO-ß, 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-1ß modulated the expression of various cytokines in cultured CECs, its absence in tear fluid and CIC samples suggests that IL-1ß does not play a modulatory role in moderate dry eye.