The Effect of Lysosomal pH on Lactoferrin-Dependent Iron Uptake in Tritrichomonas foetus

Abstract

Tritrichomonas foetus is a parasitic protozoan which causes a sexually transmitted disease of cattle. The establishment of infection depends on the ability of T. foetus to acquire iron from the host as was demonstrated in experimentally infected mice¹. Most of the iron available in mucosal secretions, the environment colonised by this parasite, is rather firmly bound to host iron-binding proteins such as lactoferrin and transferrin. Trichomonads as well as other pathogens therefore evolved specific mechanisms which allow them to withdraw iron from these proteins^2,3,4. It was shown recently that lactoferrin is specifically bound to the surface of T. foetus, endocytosed and transported into hydrolase containing lysosome-like organelles⁵. Although there is no direct evidence for release of iron within this cell compartment, the low pH in the lysosomes might provide a suitable environment for such process. Since information about the intracellular pH of protozoa is rather limited^6,7 and since no data are available on the pH of the endo/lysosomal compartment in trichomonads, we attempted (1) to determine the pH of the cytoplasm and the lysosome-like organelles of T. foetus, (2) to monitor pH changes in these organelles in trichomonads treated with agents inhibiting endo/lysosomal acidification, and (3) to investigate whether a pH increase in the lysosomal-like organelles influences the iron uptake from lactoferrin by T. foetus.