Characterization of mucins in human lacrimal sac and nasolacrimal duct.

Abstract

Mucins are polymers that may reduce drag and enhance tear outflow. Mucin expression and distribution in human efferent tear ducts were tested in the physiological state, and potential differences in the expression pattern were investigated in the presence of primary acquired dacryostenosis (PANDO). Expression of mucins in human lacrimal sac and nasolacrimal ducts was monitored by reverse transcription-polymerase chain reaction analysis. The presence and distribution of MUC1, -2, -4, -5AC, -5B, -6, and -7 in epithelia of the efferent tear duct passage are assessed with antisera to mucin peptide cores. Twenty normal tissues from cadavers and surgical specimens from 20 patients with PANDO were tested. mRNAs for all mucins investigated were detected in healthy human lacrimal sacs and nasolacrimal ducts. MUC6 mRNA was detected in only about half of the investigated samples. A reduced level of MUC2, -5AC, and -5B mRNAs was observed in PANDO. Immunohistochemistry revealed MUC2 in goblet cells and single epithelial cells. Both MUC5AC and -5B were detected in goblet cells forming intraepithelial mucous glands. MUC7 was present only in columnar epithelial cells of the efferent tear duct system. No immunoreactivity was observed with antibodies against MUC1, -4, and -6 peptide cores. Human efferent tear ducts express and produce a broad spectrum of mucins that is partly comparable with that in the conjunctiva and the salivary glands. The mucin diversity of the efferent tear ducts could enhance tear transport and antimicrobial defense. Reduced levels of mucin mRNA in a nonfunctioning though patent segment of the lacrimal passage, which is associated with epiphora, suggests that mucins ease tear flow through the efferent tear ducts.