Detection of transforming growth factor-alpha mRNA and protein in rat lacrimal glands and characterization of transforming growth factor-alpha in human tears.

PURPOSE To assess whether the lacrimal gland is a possible site of synthesis of transforming growth factor-alpha (TGF-alpha) and to characterize TGF-alpha biochemically in human tears. METHODS Reverse transcription-polymerase chain reaction (RT-PCR) amplification was used to analyze rat lacrimal glands for the presence of TGF-alpha mRNA. Specific monoclonal antibodies were used to localize TGF-alpha immunohistochemically in lacrimal gland tissue of rats. Human tears were analyzed for immunoreactive TGF-alpha protein using a specific radioimmunoassay, and the molecular weight of TGF-alpha in tears was characterized by Western blot analysis. RESULTS RT-PCR amplification of rat lacrimal gland RNA generated a band of the predicted 492 base pairs for TGF-alpha mRNA. Immunohistochemical staining of rat lacrimal gland localized TGF-alpha protein to lacrymocytes constituting acini but not to interacinar and intraacinar ducts of lacrimal glands. Western blot analysis of human tears detected a single band at MWt 16,000. Logit transformation of radioimmunoassay data for tears and TGF-alpha standard generated parallel displacement lines, indicating the presence of immunoreactive TGF-alpha levels in human tears with an average concentration of 100 +/- 20 pg/ml (mean +/- SEM). CONCLUSIONS Rat lacrymocytes synthesize TGF-alpha mRNA and protein, and human tears contain immunoreactive TGF-alpha, suggesting that the lacrimal gland may be an exocrine source for TGF-alpha in tears. The single MWt 16,000 form of TGF-alpha in human tears appears to be generated by an unusual proteolytically processing of the pro-TGF-alpha transmembrane precursor protein.