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Robert L. McKown, Veronica C. Vassilev, Kraig S. Bower, Denise S. Ryan, Rose K. Sia, Kyle Seifert; Immunodetection of a Lacritin-like Protein in Human Breast Milk. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4235.
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Human breast milk and tears share a number of common proteins including lysozyme, lactoferrin, albumin, secretory immunoglobulins, and mucins. Human breast milk has been used as self-medication for conjunctivitis and has been recently reported to improve corneal healing in an animal model system. One study suggested that lacritin may be expressed in normal human breast tissue and breast tumors; however, none was detected by RNA dot-blot or tissue array using samples from elderly individuals. Lacritin is prosecretory, mitogenic and when cleaved, antimicrobial. Topical application promotes sustained basal tearing in rabbits and is protective against INFG and TNF. Here we ask if lacritin can be detected in human breast milk.
Voluntarily donated breast milk samples were stored a -70º C until processing for analysis. Milk fat was removed by centrifugation and samples were analyzed by Western blot using polyclonal anti-lacritin antibodies specific for N- and C-termini. Blots included recombinant lacritin, human tear samples, and human milk samples. Detection was by chemiluminscence.
N-terminal specific lacritin antibodies produced distinct primary bands between 18 kDa - 20 kDa on the western blots for milk, tears, and recombinant lacritin. C-terminal specific lacritin antibodies produced distinct primary bands between 18 kDa - 20 kDa for tears and recombinant lacritin; however, only a faint band for milk was observed at this mobility while the primary band for milk with the C-terminal antibody was shifted up in molecular weight to approximately 75 kDa on the blot.
Anti-lacritin antibodies that detect recombinant lacritin and human tear lacritin also detect a protein in human milk with similar electrophoretic mobility suggesting that lacritin or lacritin-like proteins are expressed in human breast milk; however, levels may be low since proteomic analyses of human milk have failed to report lacritin.
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