The identification of transferrin, an iron-binding protein in rabbit tears

The iron-binding protein activity in rabbit tears was analysed using immunochemical techniques. Ouchterlony analysis showed that rabbit tears contain the iron-binding protein transferrin and that tear transferrin has complete antigenic identity with serum and milk transferrin. Immunoelectrophoresis showed that tear transferrin had the same electrophoretic mobility as serum transferrin. SDS-PAGE analysis of rabbit tears in the presence of purified milk transferrin was used to identify the tear transferrin band. The amount of transferrin in rabbit tears, quantified by an ELISA technique, ranged from 80 to 464 micrograms ml-1 with a mean of 285 micrograms ml-1. The origin of transferrin in rabbit tears is not yet clear. Immunofluorescence studies showed the presence of transferrin in cells lining the lacrimal ducts. The results presented here show that rabbit tears are markedly different from human tears. Rabbit tears contain transferrin and probably lack lactoferrin, whereas human tears contain large amounts of lactoferrin and hardly any detectable transferrin.