Human tears inhibit the coating of proteins to solid phase surfaces

The presence of surfactants in human tear samples was studied using methods employed in ELISA technology. Initial experiments whereby diluted tear samples were incubated with special polyacrylate ELISA microcuvettes showed no binding of tear-lactoferrin to the cuvettes whereas a marked binding of purified lactoferrin could be observed. In subsequent experiments it was shown that incubation of purified lactoferrin with increasing amounts of human tears resulted in a dose dependent inhibition of the binding of lactoferrin to the microcuvettes. Partial characterisation of the "coating inhibitory activity" in human tears was investigated by studying the effect of tears or isolated tear fractions on the non-specific binding of a peroxidase conjugated antibody onto the microcuvettes. Preincubation of microcuvettes with tears followed by a wash with phosphate buffered saline resulted in a marked inhibition of the adhesion of the peroxidase conjugate, suggesting that the coating inhibitory activity is caused by a binding of a factor in human tears to the solid phase. The findings reported here resemble earlier observations concerning lacrimal surfactants. The method described in this paper can be performed using a small quantity of human tears or isolated tear proteins and is therefore quite suitable for further biochemical analysis of tear surfactant activity as well as for clinical studies in patients with various tear film disorders.