Lacritin is a mitogen of human salivary gland cells as well as a stimulator of 
human corneal epithelial cells. It is expected to be an important factor in 
maintaining the surrounding ocular surface. The monkey would be a relevant 
animal model in which to study the role of lacritin in ophthalmic physiology and 
pathology. However, to our knowledge, no cDNA cloning or functional analysis of 
monkey lacritin has been performed. Thus, the purposes of this study were: (1) 
to clone the monkey ortholog of lacritin; (2) to characterize lacritin in tears 
from several species; and (3) to determine the tissues where lacritin is 
produced and secreted. cDNA for lacritin from rhesus macaque contained 547 bp, 
with 411 bp in an open reading frame (ORF) encoding a protein of 137 amino 
acids. Monkey lacritin showed 89% amino acid homology with human lacritin; one 
amino acid was deleted in all three monkey strains. The predicted MW of mature 
lacritin was 12.2 kDa, and the isoelectric point was 4.99. Lacritin showed 
anomalous migration at approximately 21.0 kDa on SDS-PAGE, as confirmed by 
immunoblotting and amino acid sequencing. Similar to native lacritin in monkey 
tears, a 21 kDa band was also detected in human tears. In contrast, no lacritin 
was observed at a similar position on SDS-PAGE in rat, rabbit and dog tears. In 
the monkey, lacritin mRNA was expressed highly in the lacrimal gland, moderately 
in the conjunctiva and the meibomian gland, and weakly in corneal epithelium. In 
primates, lacritin was produced in the lacrimal gland and secreted into tear 
fluid. These results suggest that lacritin might be important for the 
maintenance of the ocular surface in higher animals, such as monkeys and humans.