[Lacrimal gland-associated mucins. Age related production and their role in the pathophysiology of dry eye]

Abstract

Background: The secretory cells of the human lacrimal gland show a PAS-positive reaction in cytochemical staining procedures, suggesting the production of mucous substances. Recently, these substances were differentiated according to modern molecular classifications.

Results: Expression studies detected mRNA for MUC1, MUC4, MUC5AC, MUC5B, MUC6, and MUC7, whereas MUC2 transcripts were absent in all samples investigated. Immunohistochemistry revealed membrane-bound MUC1 at the apical surface of acinar cells, MUC5AC associated with goblet cells of excretory ducts, MUC5B and MUC7 in the cytoplasm of acinar cells, and MUC7 also in epithelial cells of excretory ducts. MUC2 (RT-PCR negative) and MUC6 (RT-PCR positive) were not detectable by immunohistochemistry. MUC4 mRNA was present in all samples from patients treated for dry eye but only in 6 of 30 glands from individuals who did not receive treatment with artificial tears. Dot-blot analyses clearly revealed increased amounts of MUC4, MUC5AC and MUC5B in the glands of elderly women who received treatment for dry eye as compared to the remaining samples.

Conclusion: These results confirm that the human lacrimal gland synthesizes a spectrum of mucins, some of which might be involved in the pathophysiology of dry eye syndrome.