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Robert L. McKown, N. Gandia, J. K. Wilburn, K. S. Bower, R. K. Sia, D. S. Ryan, K. Seifert, G. W. Laurie; Lack of Diurnal Variation of the Human Tear Protein Lacritin in Healthy Adults. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3713.
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Lacritin is a human tear protein that is prosecretory, mitogenic, antimicrobial and promotes sustained basal tearing in rabbits (Samudre, et al., IVOS, 2010). Mass spec studies have shown that lacritin is selectively downregulated in blepharitis and dry eye patients. Several tear proteins such as lysozyme and angiostatin exhibit diurnal variations in normal individuals. Here we ask if lacritin levels in tear samples from healthy adults are subject to variations during the diurnal cycle.
Tears were collected from the lower cul-de-sac from 100 healthy individuals using a polyester fiber rod (Transorb Wick, Filtrona, Richmond, VA). Single tear samples were collected at random times from 66 healthy subjects ranging in age from 21-52. Multiple samples were collected from 34 individuals ages 24-52 for the diurnal study at time 0, (7:30-8:30 am), 4 hr (11:30 am-12:30 pm), 8 hr (4:30 pm-5:30 pm), and 24 hr (7:30 am-8:30 am the following day). Rabbit antiserum made against lacritin was used in a direct ELISA to quantitate lacritin present in the tear samples.
The amount of lacritin present in tears from healthy individuals (n=66) was ~ 4.5% with no significant difference in age groups. Preliminary results from the diurnal study (n=34) suggest that there is no significant difference in the amount of lacritin in tears collected at various time points during normal daylight hours (7:30 am-5:30 pm), with average values from the time points between 4-5%.
Immunoanalysis suggest that human lacritin comprises approximately 4-5% of total tear protein in healthy individuals with no significant differences between males and females. The diurnal study suggests that levels of lacritin produced in healthy individuals do not fluctuate significantly during normal daylight hours. This finding will help guide future study design in healthy and diseased individuals.
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