TFF peptides in the human efferent tear ducts

To determine whether the lining epithelium of the human lacrimal sac and nasolacrimal duct synthesizes TFF peptides (formerly P-domain peptides, trefoil factors), a family of mucin-associated secretory peptides.

Expression of TFF peptides in human lacrimal sac and nasolacrimal ducts was monitored by reverse transcription-polymerase chain reaction and Western blot analysis. Antisera specific for TFF peptides were used in immunohistochemical analysis to determine the presence and distribution of all three TFF peptides in epithelia of the lacrimal passage. The samples investigated originated from tissue obtained during surgery (18 patients) and postmortem tissue (10 specimens).

mRNA expression of TFF1 and TFF3, but not TFF2, was detected in human lacrimal sac and nasolacrimal duct. TFF1 was detected in only approximately 50% of the investigated probes, whereas TFF3 was present in all samples. Immunohistochemistry revealed TFF1 (if present) to be associated with goblet cells forming intraepithelial mucous glands. TFF3 occurred in epithelial cells of the lacrimal sac and the nasolacrimal duct as well as in the acinar cells of subepithelial serous glands, but appeared to be absent in goblet cells.

The epithelium of the nasolacrimal ducts synthesizes TFF3 and in some cases also TFF1. In contrast to the human conjunctiva, in which TFF3 is detectable only in goblet cells, TFF3 of the lacrimal sac and nasolacrimal duct is produced in large amounts by epithelial cells as well as by serous glands, but not-or in small amounts only-by goblet cells. This is comparable with localization of TFF3 in the major salivary glands. Thus, TFF3 may have a special function in tear transport through the lacrimal passage comparable to its function on the ocular surface, because the peptide, together with TFF1, may contribute to the rheologic properties of the tear film. Moreover, the TFF peptides may also influence epithelial healing with their motogenic properties.