Macrophages play crucial roles in innate immune response and in the priming of adaptive immunity, and are characterized by their phenotypic heterogeneity and plasticity. Reprogramming intracellular metabolism in response to microenvironmental signals is required for M1/M2 macrophage polarization and function. Here we assessed the influence of iron on the polarization of the immune response in vivo and in vitro. Iron-enriched diet increased M2 marker Arg1 and Ym1 expression in liver and peritoneal macrophages, while iron deficiency decreased Arg1 expression. Under LPS-induced inflammatory conditions, low iron diet exacerbated the proinflammatory response, while the IL-12/IL-10 balance decreased with iron-rich diet, thus polarizing toward type 2 response. Indeed, in vitro macrophage iron loading reduced the basal percentage of cells expressing M1 co-stimulatory CD86 and MHC-II molecules. Further, iron loading of macrophages prevented the pro-inflammatory response induced by LPS through reduction of NF-κB p65 nuclear translocation with decreased iNOS, IL-1β, IL-6, IL-12 and TNFα expression. The increase of intracellular iron also reduced LPS-induced hepcidin gene expression and abolished ferroportin down-regulation in macrophages, in line with macrophage polarization. Thus, iron modulates the inflammatory response outcome, as elevated iron levels increased M2 phenotype and negatively regulated M1 proinflammatory LPS-induced response.

Hereditary hemochromatosis (HH) is a common autosomal recessive genetic disorder of iron metabolism. The HFE candidate gene encoding an HLA class I-like protein involved in HH was identified in 1996. Two missense mutations have been described: C282Y, accounting for 80% to 90% of HH chromosomes, and H63D, which is associated with a milder form of the disease representing 40% to 70% of non-C282Y HH chromosomes. We report here on the analysis of C282Y, H63D, and the 193A→T substitution leading to the S65C missense substitution in a large series of probands and controls. The results confirm that the C282Y substitution was the main mutation involved in hemochromatosis, accounting for 85% of carrier chromosomes, whereas the H63D substitution represented 39% of the HH chromosomes that did not carry the C282Y mutation. In addition, our screening showed that the S65C substitution was significantly enriched in probands with at least one chromosome without an assigned mutation. This substitution accounted for 7.8% of HH chromosomes that were neither C282Y nor H63D. This enrichment of S65C among HH chromosomes suggests that the S65C substitution is associated with the mild form of hemochromatosis.

Hereditary hemochromatosis is a genetically heterogeneous disease of iron metabolism. The most common form of the disorder is an adult-onset form that has mainly been associated with the HFE pC282Y/pC282Y genotype. The phenotypic expression of this genotype is very heterogeneous and could be modulated by both environmental factors and modifier genes. The non-HFE hereditary hemochromatosis forms include a juvenile onset form associated with mutations in HAMP. From a cohort of 392 C282Y homozygous patients, we found 5 carriers of an additional HAMP mutation at the heterozygous state (pR59G, pG71D, or pR56X). We found that iron indices of these 5 patients were among the most elevated of the cohort. Moreover, we specified that the HAMP mutations were not detected in 300 control subjects. These results revealed that mutations in HAMP might increase the phenotypic expression of the pC282Y/pC282Y genotype. From a cohort of 31 patients with at least one chromosome lacking an HFE mutation, we further identified 4 males carrying a heterozygous HAMP mutation (pR59G or pG71D). Based on a digenic model of inheritance, these data suggest that the association of heterozygous mutations in the HFE and HAMP genes could lead, at least in some cases, to an adultonset form of primary iron overload.

Hereditary hemochromatosis is a common inherited disorder characterized by iron overload. A single mutation (C282Y) in the HFE gene is present in 80-95% of cases in populations of northern European extraction. The disorder presents a large phenotypic heterogeneity, and its expression can be influenced by environmental factors. This 1977-2002 study aimed to identify the influence of alcohol consumption on expression of the disease. The authors retrospectively registered 378 C282Y-homozygous patients treated in a blood center of western Brittany, France. In this cohort, 33 patients reported excessive alcohol consumption (8.7%). Those subjects presented significantly increased iron parameters (serum ferritin: 1745.2 vs. 968.7 microg/liter, p< 0.0001; serum iron: 39.9 vs. 36.0 micromol/liter, p = 0.0040; transferrin saturation: 87.1 vs. 80.1%, p = 0.0071) and elevated liver enzymes (alanine aminotransferase: 66.3 vs. 41.1 IU/liter, p = 0.0003; aspartate aminotransferase: 56.2 vs. 34.9 IU/liter, p = 0.0002). Their risk of skin pigmentation was also higher (odds ratio = 3.4, p = 0.0006). Results remained unchanged after adjustment. This study provides precise quantitative data about the impact of alcohol on expression of hereditary hemochromatosis in C282Y-homozygous patients. Excessive alcohol consumption accentuates disease expression and therefore the risk of cirrhosis and cancer. Consequently, these patients should be encouraged to consume very moderate quantities of alcohol.

The most common form of hereditary haemochromatosis is an adult-onset condition usually associated with the HFE C282Y/C282Y genotype. The phenotypic expression of this genotype is heterogeneous and depends on a complex interplay of genetic and non-genetic factors. The aim of the present study was to determine if mutations in the recently identified HJV gene were associated with more severe iron overload phenotypes in C282Y homozygous patients. From a cohort of 310 C282Y homozygous patients, we found nine (six males and three females) with an additional HJV missense mutation in the heterozygous state (S105L, E302K, N372D, R335Q or the previously described L101P and G320V). The iron indices of eight patients appeared to be more severe than those observed in C282Y homozygous patients of identical sex and similar age ranges. The mean serum ferritin concentration of the six males with an HJV mutation was significantly higher than that of C282Y homozygous males without an additional mutation [2350.3 (sigma=1429.9) versus 1227.2 (sigma=1130.1) microg/l; P=0.0233, Student's t-test]. We have recently reported that mutations in the gene that encodes hepcidin (HAMP) could explain one part of the C282Y/C282Y-related phenotypic heterogeneity by accentuating the iron burden. Our new data reveal that mutations in the HJV gene could be associated with a similar effect. Taken together, these results emphasize that a search for modifier genes could enable us to more precisely distinguish those C282Y homozygous patients with a higher risk to develop a severe iron overload and, consequently, clinical complications.

Haemochromatosis is a common autosomal recessive genetic disorder of iron metabolism. A candidate gene was recently identified (HLA-H) and two amino acid substitutions (C282Y and H63D) were characterized. Haemochromatosis probands (n = 478) from Brittany were selected from their iron status markers, primarily serum iron, serum ferritin and transferrin saturation. We investigated the relationships between haemochromatosis phenotype and genotypes at the HLA-H locus and surrounding markers. As already reported, we observed that the C282Y substitution is unambiguously associated with the haemochromatosis phenotype, haemochromatosis patients homozygous for the substitution (Tyr/Tyr) accounting for 81.2% of all haemochromatosis patients. A clear heterogeneity in serum ferritin and transferrin saturation values, and in iron removed by phlebotomy was observed among haemochromatosis patients that is correlated with the presence of two subgroups of individuals homozygous and non-homozygous for the mutant allele C282Y, the latter being characterized by lower phenotypic values. In this subgroup, sequencing did not reveal any other mutation in the HLA-H gene, hence the genotype remained unclear. Thus, an additional non-genetic cause, other mutations or another gene can not be excluded as explanations for the results in these patients.

Iron is an essential element that is required for oxygen transfer, redox, and metabolic activities in mammals and bacteria. Mycobacteria, some of the most prevalent infectious agents in the world, require iron as growth factor. Mycobacterial-infected hosts set up a series of defense mechanisms, including systemic iron restriction and cellular iron distribution, whereas mycobacteria have developed sophisticated strategies to acquire iron from their hosts and to protect themselves from iron’s harmful effects. Therefore, it is assumed that host iron and iron-binding proteins, and natural or synthetic chelators would be keys targets to inhibit mycobacterial proliferation and may have a therapeutic potential. Beyond this hypothesis, recent evidence indicates a host protective effect of iron against mycobacterial infections likely through promoting remodeled immune response. In this review, we discuss experimental procedures and clinical observations that highlight the role of the immune response against mycobacteria under various iron availability conditions. In addition, we discuss the clinical relevance of our knowledge regarding host susceptibility to mycobacteria in the context of iron availability and suggest future directions for research on the relationship between host iron and the immune response and the use of iron as a therapeutic agent.

Moderate iron diet supplementation diminished inflammation and growth of M. bovis BCG via enhanced reactive oxygen species production, immune cell activation, and local hepcidin expression.