Acquisition of iron (Fe) within a mammalian host is essential for the growth and virulence of most pathogenic organisms. We have studied the extent to which different Fe sources can be utilized by the promastigote form of the parasite Leislmania chagasi (Lc). the cause of South American visceral leishmaniasis. In previous work (Heel Immun 62:3262-3269,1994), we demonstrated that Fe bound to lactoferrin (LF) or transfer (TF) supported growth at Fe concentrations of 8 \M. However, the onset of growth was delayed with FeTF but not with FeLF. Promastigotes were shown to take up "Fe from LF or TF, but uptake from LF was more rapid. Fe acquisition from LF and TF also varied with the growth stage of the organism (log > stationary). The inability to detect any to-derived siderophores or evidence of LF or TF cleavage led us to investigate the presence of a specific promastigote LF and/or TF receptor. Parasites (1.6 x 107/ml) were Incubated for 30 minutes at 4°C with labeled LF or TF (60 nM to 600 nM). Parallel cold inhibition was achieved with 100-fold higher concentrations of non-radioactive ligand. Using this system, we demonstrated specific and saturate binding of LF to i.e. Binding of ""l-labeled LF was inhibited by cold LF, but not cold TF. Binding of human apo-LF, human Fe-LF, and bovine apo-LF was similar, as was LF binding to log and stationary phase promastigotes. Scatchard analyses suggest that the promastigote LF receptor has a KO of 350 M'7 with approximately 100,000 receptors per cell. Saturate binding of 1Kl-labeled Fe TF to Lu was also detected, but at a much lower magnitude than with LF. Similar binding of Fe-TF was seen with log vs stationary phase organisms. No binding of apo-TF was detectable. In contrast to LF, saturable binding of I Fe-TF was inhibited by both cold TF and cold LF. In summary, Lc promastigotes specifically bind LF and Fe-TF. Kinetics suggest this binding is receptor-mediated. Whether TF binds to the same or different receptor remains to be elucidated. Understanding the mechanisms of Fe uptake by Lc could have important implications fAAor the treatment and prevention of leishmania infection.
|Journal of Investigative Medicine
|Published - 1996
ASJC Scopus subject areas
- General Biochemistry, Genetics and Molecular Biology