Iron regulates growth of Trichomonas vaginalis and the expression of immunogenic trichomonad proteins

Iron is an essential nutrient for Trichomonas vaginalis and is acquired via highly specific receptor-mediated mechanisms from the host. Responses of T. vaginalis to conditions of iron limitation or iron excess were analysed in order to determine whether iron levels in the growth medium regulate certain properties of the parasite. When compared with organisms grown in excess iron, iron limitation resulted in greater than or equal to 80% lower rates of protein synthesis and greater than or equal to 3-fold decreases in cell densities. These parasites also exhibited generation times of approximately 10 hours, 2.5-fold longer than organisms grown in the usual complex medium. Iron-restricted growth also resulted in increased binding of lactoferrin by trichomonads, which paralleled elevated expression of the lactoferrin-binding receptor protein having a relative molecular mass of 136,000 daltons (136 kDa). A Mr 126 kDa protein was concomitantly repressed in low-iron-grown parasites. The greater amounts of lactoferrin bound by iron-depleted T. vaginalis organisms corresponded with both the expression of additional receptors onto trichomonal surfaces and increased affinity of the receptor for the lactoferrin molecule. Finally, immunoblot analysis of parasites grown under high- and low-iron conditions using sera from patients with trichomoniasis further revealed the synthesis by T. vaginalis of at least 19 iron-regulated immunogens, and patients' sera also detected the lactoferrin receptor. These data not only show the overall importance of iron to the biology of this protozoan, but illustrate the in vivo iron modulation of gene expression of the biofunctional lactoferrin receptor and other immunogens.