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Correction of the iron overload defect in beta-2-microglobulin knockout mice by lactoferrin abolishes their increased susceptibility to tuberculosis.

Schaible UE, Collins HL, Priem F, Kaufmann SH - J. Exp. Med. (2002)

Bottom Line: This protein regulates transferrin receptor mediated iron uptake and mutations in its gene cause hereditary iron overload (hemochromatosis).Conversely, iron overload in the immunocompetent host exacerbated disease.Consistent with this, iron deprivation in infected resting macrophages was detrimental for intracellular mycobacteria.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institute for Infection Biology, Schumannstrasse 21-22, D-10117 Berlin, Germany. schaible@mpiib-berlin.mpg.de

ABSTRACT
As a resident of early endosomal phagosomes, Mycobacterium tuberculosis is connected to the iron uptake system of the host macrophage. beta-2-microglobulin (beta2m) knockout (KO) mice are more susceptible to tuberculosis than wild-type mice, which is generally taken as a proof for the role of major histocompatibility complex class I (MHC-I)-restricted CD8 T cells in protection against M. tuberculosis. However, beta2m associates with a number of MHC-I-like proteins, including HFE. This protein regulates transferrin receptor mediated iron uptake and mutations in its gene cause hereditary iron overload (hemochromatosis). Accordingly, beta2m-deficient mice suffer from tissue iron overload. Here, we show that modulating the extracellular iron pool in beta2m-KO mice by lactoferrin treatment significantly reduces the burden of M. tuberculosis to numbers comparable to those observed in MHC class I-KO mice. In parallel, the generation of nitric oxide impaired in beta2m-KO mice was rescued. Conversely, iron overload in the immunocompetent host exacerbated disease. Consistent with this, iron deprivation in infected resting macrophages was detrimental for intracellular mycobacteria. Our data establish: (a) defective iron metabolism explains the increased susceptibility of beta2m-KO mice over MHC-I-KO mice, and (b) iron overload represents an exacerbating cofactor for tuberculosis.

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Iron overload in β2m KO mice and susceptibility to M. tuberculosis of experimentally iron overloaded mice. (A) Iron-specific staining by Prussian blue of liver sections revealed iron overload in β2m–KO as compared with B6 mice (representative specimens from one out of five mice per group). (B) Iron overload in β2m–KO mice was verified by measuring iron content in organs of each mouse strain (data from five mice ± SD out of three experiments). (C) Elevated iron concentrations in organs from mice treated with Fe3+Ci (values from five mice ± SD, one out of three experiments). (D) Experimental iron overload increased growth of M. tuberculosis in B6 mice. Mice (n = 5) were infected with M. tuberculosis by aerosol and treated with Fe via the drinking water. Bacterial load was measured in the lungs at day 15 (**P < 0.005 as determined by the non paired Mann-Whitney test; one representative experiment out of three).
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fig1: Iron overload in β2m KO mice and susceptibility to M. tuberculosis of experimentally iron overloaded mice. (A) Iron-specific staining by Prussian blue of liver sections revealed iron overload in β2m–KO as compared with B6 mice (representative specimens from one out of five mice per group). (B) Iron overload in β2m–KO mice was verified by measuring iron content in organs of each mouse strain (data from five mice ± SD out of three experiments). (C) Elevated iron concentrations in organs from mice treated with Fe3+Ci (values from five mice ± SD, one out of three experiments). (D) Experimental iron overload increased growth of M. tuberculosis in B6 mice. Mice (n = 5) were infected with M. tuberculosis by aerosol and treated with Fe via the drinking water. Bacterial load was measured in the lungs at day 15 (**P < 0.005 as determined by the non paired Mann-Whitney test; one representative experiment out of three).

Mentions: To evaluate the iron status of β2m–KO mice, the total Fe content of the organs from β2m–KO mice and B6 controls was compared by Prussian blue staining and chemical analysis. Consistent with previous findings, β2m–KO mice revealed Fe overload, notably in liver and spleen (10–12; Fig. 1, A and B) . To determine whether iron overload contributes to increased susceptibility to tuberculosis, Fe3+Ci was administered to B6 mice via the drinking water. When compared with untreated animals, this diet led to enhanced Fe values in liver, spleen, and lung (Fig. 1 C). These mice were infected by aerosol with a low dose of M. tuberculosis. At 15 d after infection, the mycobacterial burdens in the lungs were approximately 10-fold higher in Fe-overloaded as compared with nontreated mice (Fig. 1 D). Hence, experimental Fe overload exacerbated tuberculosis in immunocompetent mice, consistent with one other study (13) and reflecting the situation in β2m–KO animals. In line with these in vivo observations, the addition of excess Fe to complete mycobacterial medium enhanced bacterial growth. Although not statistically significant, the increase in growth rate in the presence of excess iron was observed in all experiments (Fig. 2, A and B) . Furthermore, chelation of free Fe by deferroxamine inhibited growth of M. tuberculosis, which was rescued by adding a surplus amount of Fe (Fig. 2 B).


Correction of the iron overload defect in beta-2-microglobulin knockout mice by lactoferrin abolishes their increased susceptibility to tuberculosis.

Schaible UE, Collins HL, Priem F, Kaufmann SH - J. Exp. Med. (2002)

Iron overload in β2m KO mice and susceptibility to M. tuberculosis of experimentally iron overloaded mice. (A) Iron-specific staining by Prussian blue of liver sections revealed iron overload in β2m–KO as compared with B6 mice (representative specimens from one out of five mice per group). (B) Iron overload in β2m–KO mice was verified by measuring iron content in organs of each mouse strain (data from five mice ± SD out of three experiments). (C) Elevated iron concentrations in organs from mice treated with Fe3+Ci (values from five mice ± SD, one out of three experiments). (D) Experimental iron overload increased growth of M. tuberculosis in B6 mice. Mice (n = 5) were infected with M. tuberculosis by aerosol and treated with Fe via the drinking water. Bacterial load was measured in the lungs at day 15 (**P < 0.005 as determined by the non paired Mann-Whitney test; one representative experiment out of three).
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2194267&req=5

fig1: Iron overload in β2m KO mice and susceptibility to M. tuberculosis of experimentally iron overloaded mice. (A) Iron-specific staining by Prussian blue of liver sections revealed iron overload in β2m–KO as compared with B6 mice (representative specimens from one out of five mice per group). (B) Iron overload in β2m–KO mice was verified by measuring iron content in organs of each mouse strain (data from five mice ± SD out of three experiments). (C) Elevated iron concentrations in organs from mice treated with Fe3+Ci (values from five mice ± SD, one out of three experiments). (D) Experimental iron overload increased growth of M. tuberculosis in B6 mice. Mice (n = 5) were infected with M. tuberculosis by aerosol and treated with Fe via the drinking water. Bacterial load was measured in the lungs at day 15 (**P < 0.005 as determined by the non paired Mann-Whitney test; one representative experiment out of three).
Mentions: To evaluate the iron status of β2m–KO mice, the total Fe content of the organs from β2m–KO mice and B6 controls was compared by Prussian blue staining and chemical analysis. Consistent with previous findings, β2m–KO mice revealed Fe overload, notably in liver and spleen (10–12; Fig. 1, A and B) . To determine whether iron overload contributes to increased susceptibility to tuberculosis, Fe3+Ci was administered to B6 mice via the drinking water. When compared with untreated animals, this diet led to enhanced Fe values in liver, spleen, and lung (Fig. 1 C). These mice were infected by aerosol with a low dose of M. tuberculosis. At 15 d after infection, the mycobacterial burdens in the lungs were approximately 10-fold higher in Fe-overloaded as compared with nontreated mice (Fig. 1 D). Hence, experimental Fe overload exacerbated tuberculosis in immunocompetent mice, consistent with one other study (13) and reflecting the situation in β2m–KO animals. In line with these in vivo observations, the addition of excess Fe to complete mycobacterial medium enhanced bacterial growth. Although not statistically significant, the increase in growth rate in the presence of excess iron was observed in all experiments (Fig. 2, A and B) . Furthermore, chelation of free Fe by deferroxamine inhibited growth of M. tuberculosis, which was rescued by adding a surplus amount of Fe (Fig. 2 B).

Bottom Line: This protein regulates transferrin receptor mediated iron uptake and mutations in its gene cause hereditary iron overload (hemochromatosis).Conversely, iron overload in the immunocompetent host exacerbated disease.Consistent with this, iron deprivation in infected resting macrophages was detrimental for intracellular mycobacteria.

View Article: PubMed Central - PubMed

Affiliation: Max-Planck-Institute for Infection Biology, Schumannstrasse 21-22, D-10117 Berlin, Germany. schaible@mpiib-berlin.mpg.de

ABSTRACT
As a resident of early endosomal phagosomes, Mycobacterium tuberculosis is connected to the iron uptake system of the host macrophage. beta-2-microglobulin (beta2m) knockout (KO) mice are more susceptible to tuberculosis than wild-type mice, which is generally taken as a proof for the role of major histocompatibility complex class I (MHC-I)-restricted CD8 T cells in protection against M. tuberculosis. However, beta2m associates with a number of MHC-I-like proteins, including HFE. This protein regulates transferrin receptor mediated iron uptake and mutations in its gene cause hereditary iron overload (hemochromatosis). Accordingly, beta2m-deficient mice suffer from tissue iron overload. Here, we show that modulating the extracellular iron pool in beta2m-KO mice by lactoferrin treatment significantly reduces the burden of M. tuberculosis to numbers comparable to those observed in MHC class I-KO mice. In parallel, the generation of nitric oxide impaired in beta2m-KO mice was rescued. Conversely, iron overload in the immunocompetent host exacerbated disease. Consistent with this, iron deprivation in infected resting macrophages was detrimental for intracellular mycobacteria. Our data establish: (a) defective iron metabolism explains the increased susceptibility of beta2m-KO mice over MHC-I-KO mice, and (b) iron overload represents an exacerbating cofactor for tuberculosis.

Show MeSH
Related in: MedlinePlus