Guinea pig tears contain lactoferrin and transferrin

The ironbinding protein lactoferrin is one of the main proteins in human tears. Until now no animal models are available to investigate the exact role of this protein on the ocular surface. We have therefore started investigations concerning the presence of ironbinding proteins in various laboratory animals. In this report the presence of lactoferrin and transferrin in guinea pig tears was investigated using an iron-binding assay, Ouchterlony immunodiffusion, ELISA and immunoblotting techniques. Guinea pig tears contain a weak ironbinding activity, which is markedly lower than that observed in human tears. Lactoferrin and transferrin were identified using the fact that guinea pig lactoferrin reacts with monoclonal and polyclonal anti human lactoferrin antibodies and that guinea pig serum transferrin reacts with an anti rabbit transferrin serum. SDS-PAGE and immunoblotting showed that, guinea pig lactoferrin and transferrin have a similar molecular weight of approximately 75 kD, which is however, definitely smaller than that of human lactoferrin and transferrin (80 kD). The amount of lactoferrin in guinea pig tears, measured in an ELISA using anti human lactoferrin antisera, was very low (equalling 600 mg/ml of human lactoferrin immunoreactivity). Transferrin in guinea pig tears was measured with an ELISA in 10 guinea pigs and resulted in a mean concentration of 22.3 micrograms/ml. The species comparisons performed until now indicate that human tears remain unique in their high content of lactoferrin.