In primary Sjögren's syndrome (SS), ocular surface changes within the conjunctival epithelium include lymphocytic infiltration, squamous cell metaplasia, and a reduction in goblet cell number. These changes may be the simple result of increased mechanical abrasion secondary to dryness. Alternatively, they may represent a local response to ocular and/or systemic inflammatory processes, perhaps in response to Epstein-Barr viral (EBV) infection, an agent recently implicated in the etiology of SS. To determine whether inflammatory processes or local infection by EBV contribute to the ocular surface pathology of SS, we examined the expression of inflammatory cell surface markers, cytokines, and EBV gene products within the ocular conjunctiva of patients with SS.
Ocular conjunctival tissue was isolated from patients with primary SS and nondry eye control patients by impression cytology or direct biopsy. These specimens were examined by immunofluorescence microscopy and reverse-transcriptase polymerase chain reaction (RT-PCR) for the expression of various markers.
The authors found the frequency of expression of HLA-DR (P < 0.0001), ICAM-1 (P < 0.035), and IL-6 (P < 0.0001) to be significantly elevated in patients with primary SS versus nondry eye control patients. The IL-2 receptor and cytokines IL-1 beta and IL-8 were each found to be expressed with relatively high frequency in both patient populations, whereas mRNAs encoding cytokines IL-2, IFN-gamma, GM-CSF, and TGF-beta were not reproducibly detectable in either population. Messenger RNA encoding a marker for passive-latent EBV infection (EBNA-1) was detected with high frequency in both SS and normal populations. The EBV IL-10 analog BCRF-1 was expressed with low frequency in the SS population; however, these levels were not significantly different from the control population. The expression of two other markers of EBV infection, latent membrane protein (LMP, a lytic and latent marker), and BZLF-1 (putative latent-lytic switch gene) was undetectable in either study population.
Based on the increased expression of the cell surface molecules HLA-DR and ICAM-1, and the inflammatory cytokine IL-6, the authors propose that local inflammatory processes contribute to the ocular surface changes and ocular surface dryness associated with primary SS.