Tear Protein Composition and the Effects of Stimulus

Abstract

Tear protein profiles are significantly affected by stimulus and by the use of invasive tear collection techniques. The importance of stimulus control has been largely overlooked until recent times. This is most likely due to the fact that the main three tear proteins, lactoferrin, tear specific prealbumin (TSP) and lysozyme, show very little change over a wide range of stimulus conditions (Fullard and Snyder, 1990; Fullard and Tucker, 1991). Comparing non-stimulated tears collected under carefully controlled conditions with high flow-rate stimulated tears collected after discarding the initial 20 µl reveals very large differences for many tear proteins. Secretory IgA (both subclasses), IgM and IgG all show a more than 5-fold decrease in stimulated tears (Fullard and Snyder, 1990). Transferrin and albumin show a smaller, but still significant, decrease in stimulated tears. The three main lacrimal gland proteins and peroxidase undergo minimal change. Levels of the enzyme, lactate dehydrogenase (LDH) have also been shown to be significantly lower in stimulated tears (Van Haeringen and Glasius, 1974; Fullard and Carney, 1984).