Tissue expression of lipocalins in human lacrimal and von Ebner's glands: colocalization with lysozyme.
BACKGROUND
Tear-specific prealbumin is a group of proteins recently renamed as the tear lipocalins. These proteins were initially described as unique to lacrimal fluid. The tissue distribution and localization have never been thoroughly studied.


METHODS
The distribution of purified tear lipocalins was studied in many human secretions and tissues by western blots, immunohistochemistry and immunoelectron microscopy.


RESULTS
Tear lipocalin species of the same molecular weights were observed in western blot lanes loaded with tears, saliva, and protein extracts from the lacrimal and lingual von Ebner's glands. Lacrimal and von Ebner's glands contained tear lipocalins; other human tissues and secretions, including other salivary glands and taste buds, did not. Tear lipocalins colocalized with lysozyme in serous acinar cells of lacrimal and von Ebner's glands. Ultrastructurally, tear lipocalins were present on polyribosomes, endoplasmic reticulum, and Golgi areas. Lipocalins were concentrated in lacrimal secretory granules in amounts commensurate with a regulated pathway.


CONCLUSIONS
Tear lipocalins are expressed and truncated similarly in lingual von Ebner's and lacrimal glands, but not at all in other human tissues. Lipocalins are expressed and secreted with lysozyme. Lipocalins are concentrated in secretory granules in an amount consistent with a regulated secretory pathway.
Department of Pathology and Ophthalmology, Jules Stein Eye Institute, UCLA School of Medicine, Los Angeles, CA 90024, USA.
B J
BJ
Glasgow
D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D015153:Blotting, Western; D002352:Carrier Proteins / Q000032:analysis* / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006041:Goats; D006801:Humans; D007124:Immunoenzyme Techniques; D007765:Lacrimal Apparatus / Q000737:chemistry*; D054835:Lipocalin 1; D008297:Male; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009113:Muramidase / Q000032:analysis / Q000276:immunology / Q000648:ultrastructure; D011817:Rabbits; D012463:Saliva / Q000378:metabolism; D012471:Salivary Proteins and Peptides / Q000032:analysis* / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification; D013666:Tears / Q000378:metabolism; D014059:Tongue / Q000737:chemistry* / Q000648:ultrastructure
D002352:Carrier Proteins; C518443:LCN1 protein, human; D054835:Lipocalin 1; D012471:Salivary Proteins and Peptides; D009113:Muramidase