PURPOSE.Several small proteomic studies suggest that the prosecretory tear protein lacritin may be selectively downregulated in dry eye syndrome and in blepharitis, yet little information is available about normal baseline levels. This study assessed lacritin levels in tears from healthy individuals and addressed whether they differ according to sex, age, or time of day.METHODS. Rabbit antibodies against lacritin N-terminal peptide EDASSDSTGADPAQEAGTS (Pep Lac N-Term) were generated and characterized against human recombinant lacritin and N-65 truncation mutant. Basal tears were collected from 66 healthy individuals ranging in age from 18 to 52 years, and at four times during one 24-hour period from 34 other individuals. Lacritin levels were then analyzed by ELISA and Western blotting.RESULTS. Anti-Pep Lac N-Term bound lacritin, but not truncation mutant N-65 that lacks the N-terminal antigenic site. Tear lacritin levels followed a normal distribution with a mean of 4.2 6 1.17 ng/100 ng total tear protein. Levels differed little by age or sex, and decreased slightly between 4 and 8 hours in a 24-hour cycle. Tear-blocking effects were minimal, as suggested by spiking of tears with recombinant lacritin.CONCLUSIONS. Anti-Pep Lac N-Term-detectable lacritin comprises~4.2 ng/100 ng total tear protein in healthy individuals, with no significant differences between males and females or among individuals between 18 and 52 years old. Levels decrease slightly in the late afternoon. These findings provide a baseline for future immunodiagnostic studies of lacritin in dry eye and other ocular diseases. (Invest Ophthalmol Vis Sci. 2012;53:6610-6616 Lacritin's ability to stimulate tear production makes it an interesting protein to study for its potential involvement in dry eye syndrome and other eye-related diseases. Dry eye affects the lives of over 25 million Americans, yet it is poorly understood and lacks sensitive early-stage diagnostics. Current tests are more appropriate for later disease stages, making difficult the diagnosis of patients with mild to moderate symptoms. 3 Moreover, tests such as Schirmer strips, ocular surface staining, and tear film breakup time are still not uniformly applied 4 (although standardization has improved with publication of the International Dry Eye Workshop report 5 ), and new devices to assess tear osmolarity show promise, 6 although not in isolation. 7 Development of an assay to help diagnose both early-onset and later dry eye, recognizing that there may be different etiologies, would be of great benefit.Dry eye syndrome and other associated conditions are believed to correlate with changes in specific protein content of the ocular surface. 8 Some small proteomic studies suggest that lacritin is one of only 4% to 5% of the tear proteome that is downregulated in dry eye or dry eye-related conditions. Lacritin levels measured by mass spectroscopy analysis of tear samples were 7-fold less from 11 individuals with contact lensrelated dry eye than from 10 users of contact lenses with normal ...