Human Lacrimal Gland Secretes Proteins Belonging to the Group of Hydrophobic Molecule Transporters

Abstract

Many orbital glands and ocular surface epithelia participate to the formation of the human lacrimal tear film: the main lacrimal gland, the accessory lacrimal glands, the goblet cells and conjunctival epithelial cells, the cornea and the meibomian glands. Consequently, human tears are constituted of a complex mixture of proteins and glycoproteins, with or without enzymatic activities, metabolites, electrolytes and lipids. Furthermore, serum proteins, generally accepted as derived from the ocular surface vessels and indicative of collection trauma, are also present. Three lacrimal gland proteins, lactoferrin, lysozyme and tear specific prealbumin account for the major part of protein content. Our presentation will deal with tear specific prealbumin, which is, as further demonstrated, an inappropriate term. Bonavida, Sapse and Sercarz (1969) described, for the first time, a tear specific prealbumin, present at high levels in tears of humans and several animal species (rabbit, rat, monkey). Its electrophoretic mobility was larger than albumin and it was absent from serum and other biological fluids such as cerebrospinal fluid, saliva, nasal secretion and sweat. Its local synthesis by main lacrimal gland was shown by culturing lacrimal gland slices in the presence of radiolabeled amino-acids (Bonavida et al., 1969). Using higher resolution electrophoretic methods, we demonstrated that Bonavida’s team had not described a single protein but a group of at least six proteins whose molecular weight ranged from 15 to 20 kDa with isoelectric points ranging from 4.6 to 5.4 (Gachon et al., 1979; Gachon, Lambin and Dastugue, 1980); we called them ‘Proteins Migrating Faster than Albumin’ (PMFAs) in order to clearly differentiate them from transthyretin (current denomination of prealbumin).KeywordsLacrimal GlandRetinol Binding ProteinComplete Amino Acid SequenceGland ProteinConjunctival Epithelial CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.