To compare epidermal growth factor (EGF) concentration in tear fluid and levels of inflammatory cytokines in the conjunctival epithelium of patients with Sjögren's syndrome keratoconjunctivitis sicca with those of normal controls.
Schirmer 1 tear testing, corneal fluorescein staining and conjunctival impression cytology for quantitation of goblet cell density were performed in ten patients with Sjögren's syndrome-associated keratoconjunctivitis sicca and ten asymptomatic normal controls. ELISA was used to detect the concentration of EGF in tear fluid and interleukin 6 in lysates of conjunctival cytology specimens obtained from all subjects. The levels of RNA transcripts encoding inflammatory cytokines [interleukin 1alpha_(IL-1alpha), interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor alpha_(TNF-alpha), and transforming growth factor beta1 (TGF-beta1)] as well as a housekeeping gene (G3PDH) were evaluated in conjunctival cytology specimens taken from all subjects by semiquantitative competitive reverse transcriptase polymerase chain reaction (RT-PCR).
Decreased tear fluid EGF concentration was noted in Sjögren's syndrome patients (mean 0.68 +/- 0.59 ng/ml) compared to controls (mean 1.66 +/- 0.45 ng/ml, P = 0.004). Significantly increased levels of IL-1alpha, IL-6, IL-8, TNF-alpha and TGF-beta1 RNA transcripts were found in the conjunctival epithelium of Sjögren's syndrome patients compared to controls (P < 0.05), while the level of G3PDH was similar in both groups. The concentration of IL-6 protein was significantly higher in Sjögren's syndrome conjunctiva samples (P = 0.012). Tear EGF concentration correlated with Schirmer 1 scores (rho 0.767, P < 0.001), corneal fluorescein staining scores (rho -0.562, P = 0.01), conjunctival goblet cell density (rho 0.661, P = 0.001) and the levels of IL-1alpha_and IL-8 RNA in the conjunctival epithelium (rho -0.677 and -0.747, respectively, P = 0.001). Both IL-1alpha_and IL-8 RNA in the conjunctival epithelium increased as Schirmer 1 scores decreased (P </= 0.001). IL-8 RNA level correlated with corneal fluorescein staining (rho 0.690, P = 0.001) and conjunctival goblet cell density (rho -0.767, P < 0.001). A significant decrease in IL-8 RNA level, corresponding to improvement in irritation symptoms and ocular surface disease, was observed in six eyes after two weeks of topical corticosteroid therapy.
The balance of cytokines in the tear fluid and conjunctival epithelium is altered in Sjögren's syndrome. The severity of keratoconjunctivitis sicca in this condition increases as tear fluid EGF concentration decreases and levels of inflammatory cytokines in the conjunctival epithelium increase. These findings provide new insight into the pathogenesis of keratoconjunctivitis and provide potential targets for therapy.