PURPOSE: Lacritin is a human tear glycoprotein that promotes basal tear protein 
secretion in cultured rat lacrimal acinar cells and proliferation of 
subconfluent human corneal epithelial cells. When topically added to rabbit 
eyes, lacritin promotes basal tearing. Despite these activities on several 
species, lacritin's presence in nonprimate tears or other tissues has not been 
explored. Here we probed for lacritin in normal horse tears.
METHODS: Sequences were collected from the Ensembl genomic alignment of human 
LACRT gene with high-quality draft horse genome (EquCab2.0) and analyzed. Normal 
horse tears were collected and assayed by Western blotting, ELISA, and mass 
spectrometry. Newly generated rabbit antibodies, respectively, against N- and 
C-terminal regions of human lacritin were employed.
RESULTS: Identity was 75% and 45%, respectively, at nucleotide and protein 
levels. Structural features were conserved, including a C-terminal amphipathic 
α-helix. Anti-C-terminal antibodies strongly detected a ∼13 kDa band in horse 
tears that was validated by mass spectrometry. In human tears, the same antibody 
detected uncleaved lacritin (∼24 kDa) strongly and C-terminal fragments of ∼13 
and ∼11 kDa weakly. Anti-N-terminal antibodies were slightly reactive with a ∼24 
kDa horse antigen and showed no reaction with the anti-C-terminal-reactive ∼13 
kDa species. Similar respective levels of horse C-terminal versus N-terminal 
immunoreactivity were apparent by ELISA.
CONCLUSIONS: Lacritin is present in horse tears, largely as a C-terminal 
fragment homologous to the mitogenic and bactericidal region in human lacritin, 
suggesting potential benefit in corneal wound repair.