Origin and biosynthesis of human tear fluid proteins

In tear fluid, a large number of proteins can be detected with electrophoretic or immunologic techniques. The composition of serum proteins in tears resembles that of whole serum. By comparison of the protein patterns resulting from different sampling methods, it was shown that serum albumin is not present in the secretion of the lacrimal gland, but is mixed with the tear fluid in the conjunctival sac. The in vitro synthesis and excretion of more than 20 protein components by the lacrimal gland could be demonstrated. Among these were lactoferrin, tear-specific prealbumin, lysozyme, and secretory IgA. The complexity of the electrophoretic protein pattern of tear fluid can be explained from the combination of the secretory activity of the lacrimal gland and the leakage of serum proteins from the circulation into the tear fluid.