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L. Braeuer, K. Jaeger, C. Kindler, F. Paulsen; Detection of Surfactant Proteins (SP-A, -B, -C, -D) in Tissues of the Human Lacrimal System and in Tears. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5563.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the expression and presence of the surfactant proteins (SP) A, B, C and D in the lacrimal apparatus, at the ocular surface and in tears in healthy and pathologic states.
Expression of mRNA for SP-A, -B, -C and -D was analyzed by RT-PCR in healthy lacrimal gland, conjunctiva, cornea and nasolacrimal ducts as well as in immortalized conjunctival and corneal epithelial cell lines. Deposition of all surfactant proteins was determined by Western blot, dot blot and immunohistochemistry in healthy tissues, in tears, aqueous humor as well as in sections of different corneal pathologies.
The presence of SP-A, -B, -C and -D on mRNA and protein level was evidenced in healthy lacrimal gland, conjunctiva, cornea and nasolacrimal duct samples. Moreover, all proteins were present in tears but were absent in aqueous humor. Immunohistochemistry revealed production of the four peptides by acinar epithelial cells of the lacrimal gland as well as epithelial cells of the conjunctiva and nasolacrimal ducts. Healthy cornea revealed weak reactivity on epithelial surface cells only. In contrast, SP-A and SP-D (but not SP-B and -C) revealed strong reactivity in cases of herpetic keratitis and corneal ulceration. Reactivity in corneal epithelium and endothelium was also seen in cases of keratoconus. Cell culture experiments revealed that SP-A and SP-D are produced by both epithelial cell lines without and after stimulation with cytokines and bacterial components.
Our results show that, in addition to SP-D, SP-A, SP-B and SP-C are peptides of the tear film. Based on the known direct and indirect antimicrobial effects of collectins, the surfactant-associated proteins A and D seem to be involved in several ocular surface diseases.
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