Hepatic damage in C282Y homozygotes relates to low numbers of CD8+ cells in the liver lobuli

Low-molecular-mass iron in healthy blood plasma is not predominately ferric citrate

Blood contains a poorly characterized pool of labile iron called non-transferrin-bound iron (NTBI). In patients with iron-overload diseases such as hemochromatosis, NTBI accumulates in the liver, heart, and other organs. This material is probably nonproteinaceous and low molecular mass (LMM). However, the number, concentration, mass, and chemical composition of NTBI species remain unknown despite decades of effort. Here, solutions of plasma from humans, pigs, horses, and mice were passed through a 10 kDa cutoff membrane, affording flow-through solutions (FTSs) containing ∼1 μM iron. The FTSs were subjected to size-exclusion liquid chromatography at pH 8.5, 6.5, and 4.5. Iron was detected by an online inductively-coupled-plasma mass spectrometer. LC-ICP-MS chromatograms of the FTSs exhibited 2-6 iron-containing species with apparent masses between 400 and 2500 Da. Their approximate concentrations in plasma were 10-8-10-7 M. Not every FTS sample contained every LMM iron species, indicating individual variations. The most reproducible iron species had apparent masses of 400 and 500 Da. Chromatograms of the FTSs from established hemochromatosis patients exhibited no significant differences relative to controls. The peak positions and intensities depended on column pH. Some FTS iron adsorbed onto the column, especially at higher pH. Column-adsorbing-iron coordinated apo-transferrin whereas the more tightly coordinated iron species did not. Ferric citrate standards exhibited LMM iron peaks that were similar to but not the same as those obtained in FTSs. The results indicate that the LMM iron species in healthy blood plasma is not primarily ferric citrate; however, this may be one of many contributing complexes.

Human Leukocyte Antigen (HLA) and Immune Regulation: How Do Classical and Non-Classical HLA Alleles Modulate Immune Response to Human Immunodeficiency Virus and Hepatitis C Virus Infections?

The genetic factors associated with susceptibility or resistance to viral infections are likely to involve a sophisticated array of immune response. These genetic elements may modulate other biological factors that account for significant influence on the gene expression and/or protein function in the host. Among them, the role of the major histocompatibility complex in viral pathogenesis in particular human immunodeficiency virus (HIV) and hepatitis C virus (HCV), is very well documented. We, recently, added a novel insight into the field by identifying the molecular mechanism associated with the protective role of human leukocyte antigen (HLA)-B27/B57 CD8⁺ T cells in the context of HIV-1 infection and why these alleles act as a double-edged sword protecting against viral infections but predisposing the host to autoimmune diseases. The focus of this review will be reexamining the role of classical and non-classical HLA alleles, including class Ia (HLA-A, -B, -C), class Ib (HLA-E, -F, -G, -H), and class II (HLA-DR, -DQ, -DM, and -DP) in immune regulation and viral pathogenesis (e.g., HIV and HCV). To our knowledge, this is the very first review of its kind to comprehensively analyze the role of these molecules in immune regulation associated with chronic viral infections.

Molecular pathogenesis and clinical consequences of iron overload in liver cirrhosis

BACKGROUND

The liver, as the main iron storage compartment and the place of hepcidin synthesis, is the central organ involved in maintaining iron homeostasis in the body. Excessive accumulation of iron is an important risk factor in liver disease progression to cirrhosis and hepatocellular carcinoma. Here, we review the literature on the molecular pathogenesis of iron overload and its clinical consequences in chronic liver diseases.

DATA SOURCES

PubMed was searched for English-language articles on molecular genesis of primary and secondary iron overload, as well as on their association with liver disease progression. We have also included literature on adjuvant therapeutic interventions aiming to alleviate detrimental effects of excessive body iron load in liver cirrhosis.

RESULTS

Excess of free, unbound iron induces oxidative stress, increases cell sensitivity to other detrimental factors, and can directly affect cellular signaling pathways, resulting in accelerated liver disease progression. Diagnosis of liver cirrhosis is, in turn, often associated with the identification of a pathological accumulation of iron, even in the absence of genetic background of hereditary hemochromatosis. Iron depletion and adjuvant therapy with antioxidants are shown to cause significant improvement of liver functions in patients with iron overload. Phlebotomy can have beneficial effects on liver histology in patients with excessive iron accumulation combined with compensated liver cirrhosis of different etiology.

CONCLUSION

Excessive accumulation of body iron in liver cirrhosis is an important predictor of liver failure and available data suggest that it can be considered as target for adjuvant therapy in this condition.

Lymphocyte gene expression signatures from patients and mouse models of hereditary hemochromatosis reveal a function of HFE as a negative regulator of CD8+ T-lymphocyte activation and differentiation in vivo

Abnormally low CD8⁺ T-lymphocyte numbers is characteristic of some patients with hereditary hemochromatosis (HH), a MHC-linked disorder of iron overload. Both environmental and genetic components are known to influence CD8⁺ T-lymphocyte homeostasis but the role of the HH associated protein HFE is still insufficiently understood. Genome-wide expression profiling was performed in peripheral blood CD8⁺ T lymphocytes from HH patients selected according to CD8⁺ T-lymphocyte numbers and from Hfe^-/- mice maintained either under normal or high iron diet conditions. In addition, T-lymphocyte apoptosis and cell cycle progression were analyzed by flow cytometry in HH patients. HH patients with low CD8⁺ T-lymphocyte numbers show a differential expression of genes related to lymphocyte differentiation and maturation namely CCR7, LEF1, ACTN1, NAA50, P2RY8 and FOSL2, whose expression correlates with the relative proportions of naïve, central and effector memory subsets. In addition, expression levels of LEF1 and P2RY8 in memory cells as well as the proportions of CD8⁺ T cells in G2/M cell cycle phase are significantly different in HH patients compared to controls. Hfe^-/- mice do not show alterations in CD8⁺ T-lymphocyte numbers but differential gene response patterns. We found an increased expression of S100a8 and S100a9 that is most pronounced in high iron diet conditions. Similarly, CD8⁺ T lymphocytes from HH patients display higher S100a9 expression both at the mRNA and protein level. Altogether, our results support a role for HFE as a negative regulator of CD8⁺ T-lymphocyte activation. While the activation markers S100a8 and S100a9 are strongly increased in CD8⁺ T cells from both, Hfe^-/- mice and HH patients, a differential profile of genes related to differentiation/maturation of CD8⁺ T memory cells is evident in HH patients only. This supports the notion that HFE contributes, at least in part, to the generation of low peripheral blood CD8⁺ T lymphocytes in HH.

T lymphocyte-derived TNF and IFN-γ repress HFE expression in cancer cells

The immune system and tumors are closely intertwined initially upon tumor development. During this period, tumors evolve to promote self-survival through immune escape, including by targeting crucial components involved in the presentation of antigens to the immune system in order to avoid recognition. Accordingly, components involved in MHC I presentation of tumor antigens are often mutated and down-regulated targets in tumors. On the other hand, the immune system has been shown to influence tumors through production of immunosuppressive cytokines, recruitment and polarization of cells favoring or impeding tumor escape or through production of anti-tumor cytokines promoting tumor rejection. We previously discovered that the hemochromatosis protein HFE, a negative regulator of iron absorption, dampens classical MHC I antigen presentation. In this study, we evaluated the impact of activated T lymphocytes purified from peripheral blood mononuclear cells (PBMC) on HFE expression in tumor cell lines. We co-cultured tumor cell lines from melanoma, lung, and kidney cancers with anti-CD3-activated PBMC and established that HFE expression is increased in tumor cell lines compared to healthy tissues, whilst being down-regulated significantly upon exposure to activated PBMC. HFE down-regulation was mediated by both CD4 and CD8 T lymphocytes, through production of soluble mediators, namely TNF and IFN-γ. These results suggest that the immune system may modulate tumor HFE expression in inflammatory conditions in order to regulate MHC I antigen presentation and promote tumor clearance.

Non-transferrin-bound iron (NTBI) uptake by T lymphocytes: evidence for the selective acquisition of oligomeric ferric citrate species

Iron is an essential nutrient in several biological processes such as oxygen transport, DNA replication and erythropoiesis. Plasma iron normally circulates bound to transferrin. In iron overload disorders, however, iron concentrations exceed transferrin binding capacity and iron appears complexed with low molecular weight molecules, known as non-transferrin-bound iron (NTBI). NTBI is responsible for the toxicity associated with iron-overload pathologies but the mechanisms leading to NTBI uptake are not fully understood. Here we show for the first time that T lymphocytes are able to take up and accumulate NTBI in a manner that resembles that of hepatocytes. Moreover, we show that both hepatocytes and T lymphocytes take up the oligomeric Fe3Cit3 preferentially to other iron-citrate species, suggesting the existence of a selective NTBI carrier. These results provide a tool for the identification of the still elusive ferric-citrate cellular carrier and may also open a new pathway towards the design of more efficient iron chelators for the treatment of iron overload disorders.

Lymphocyte subsets in alcoholic liver disease

AIM

To compare lymphocyte subsets between healthy controls and alcoholics with liver disease.

METHODS

The patient cohort for this study included individuals who were suspected to have alcoholic liver disease (ALD) and who had undergone liver biopsy (for disease grading and staging, doubts about diagnosis, or concurrent liver disease; n = 56). Normal controls included patients who were admitted for elective cholecystectomy due to non-complicated gallstones (n = 27). Formalin-fixed, paraffin-embedded liver biopsy specimens were sectioned and stained with hematoxylin and eosin and Perls' Prussian blue. The non-alcoholic steatohepatitis score was used to assess markers of ALD. Lymphocyte population subsets were determined by flow cytometry. T lymphocytes were identified (CD3(+)), and then further subdivided into CD4(+) or CD8(+) populations. B lymphocytes (CD19(+)) and natural killer (NK) cell numbers were also measured. In addition to assessing lymphocyte subpopulation differences between ALD patients and controls, we also compared subsets of alcoholic patients without cirrhosis or abstinent cirrhotic patients to normal controls.

RESULTS

The patient cohort primarily consisted of older men. Active alcoholism was present in 66.1%. Reported average daily alcohol intake was 164.9 g and the average lifetime cumulative intake was 2211.6 kg. Cirrhosis was present in 39.3% of the patients and 66.1% had significant fibrosis (perisinusoidal and portal/periportal fibrosis, bridging fibrosis, or cirrhosis) in their liver samples. The average Mayo end-stage liver disease score was 7.6. No hereditary hemochromatosis genotypes were found. ALD patients (n = 56) presented with significant lymphopenia (1.5 × 10(9)/L ± 0.5 × 10(9)/L vs 2.1 × 10(9)/L ± 0.5 × 10(9)/L, P < 0.0001), due to a decrease in all lymphocyte subpopulations, except for NK lymphocytes: CD3(+) (1013.0 ± 406.2/mm(3) vs 1523.0 ± 364.6/mm(3), P < 0.0001), CD4(+) (713.5 ± 284.7/mm(3) vs 992.4 ± 274.7/mm(3), P < 0.0001), CD8(+) (262.3 ± 140.4/mm(3) vs 478.9 ± 164.6/mm(3), P < 0.0001), and CD19(+) (120.6 ± 76.1/mm(3) vs 264.6 ± 88.0/mm(3), P < 0.0001). CD8(+) lymphocytes suffered the greatest reduction, as evidenced by an increase in the CD4(+)/CD8(+) ratio (3.1 ± 1.3 vs 2.3 ± 0.9, P = 0.013). This ratio was associated with the stage of fibrosis on liver biopsy (r s = 0.342, P = 0.01) and with Child-Pugh score (r s = 0.482, P = 0.02). The number of CD8(+) lymphocytes also had a positive association with serum ferritin levels (r s = 0.345, P = 0.009). Considering only patients with active alcoholism but not cirrhosis (n = 27), we found similar reductions in total lymphocyte counts (1.8 × 10(9)/L ± 0.3 × 10(9)/L vs 2.1 × 10(9)/L ± 0.5 × 10(9)/L, P = 0.018), and in populations of CD3(+) (1164.7 ± 376.6/mm(3) vs 1523.0 ± 364.6/mm(3), P = 0.001), CD4(+) (759.8 ± 265.0/mm(3) vs 992.4 ± 274.7/mm(3), P = 0.003), CD8(+) (330.9 ± 156.3/mm(3) vs 478.9 ± 164.6/mm(3), P = 0.002), and CD19(+) (108.8 ± 64.2/mm(3) vs 264.6 ± 88.0/mm(3), P < 0.0001). In these patients, the CD4(+)/CD8(+) ratio and the number of NK lymphocytes was not significantly different, compared to controls. Comparing patients with liver cirrhosis but without active alcohol consumption (n = 11), we also found significant lymphopenia (1.3 × 10(9)/L ± 0.6 × 10(9)/L vs 2.1 × 10(9)/L ± 0.5 × 10(9)/L, P < 0.0001) and decreases in populations of CD3(+) (945.5 ± 547.4/mm(3) vs 1523.0 ± 364.6/mm(3), P = 0.003), CD4(+) (745.2 ± 389.0/mm(3) vs 992.4 ± 274.7/mm(3), P = 0.032), CD8(+) (233.9 ± 120.0/mm(3) vs 478.9 ± 164.6/mm(3), P < 0.0001), and CD19(+) (150.8 ± 76.1/mm(3) vs 264.6 ± 88.0/mm(3), P = 0.001). The NK lymphocyte count was not significantly different, but, in this group, there was a significant increase in the CD4(+)/CD8(+) ratio (3.5 ± 1.3 vs 2.3 ± 0.9, P = 0.01).

CONCLUSION

All patient subsets presented with decreased lymphocyte counts, but only patients with advanced fibrosis presented with a significant increase in the CD4(+)/CD8(+) ratio.

Hepcidin messenger RNA expression in human lymphocytes

Hepcidin regulates intracellular iron levels by interacting with and promoting the degradation of ferroportin, a membrane protein and the only known cellular iron exporter. Studies of hepcidin expression and regulation have focused on its effects in innate immunity and as a regulator of systemic iron metabolism. In the present study we characterized the expression of hepcidin messenger RNA (mRNA) in human peripheral blood mononuclear cells (PBMCs) with a focus on peripheral blood lymphocytes (PBLs). We found that (1) all human PBMCs analyzed express basal hepcidin mRNA levels; (2) hepcidin mRNA expression increases after T-lymphocyte activation; (3) expression by PBLs increases in response to challenge by holotransferrin (Fe-TF) and by ferric citrate in vitro; (4) the Fe-TF-mediated up-regulation of hepcidin decreases ferroportin expression at the cytoplasmic membrane of PBLs; and (5) silencing of tumour necrosis factor-alpha (TNF-alpha) abrogates the effect of Fe-TF. In summary, we show that hepcidin expression determines intracellular iron levels by regulating the expression of ferroportin, as described in other cells, and that inappropriately low expression of hepcidin impairs normal lymphocyte proliferation. The results establish hepcidin as a new player in lymphocyte biology.

Ceruloplasmin expression by human peripheral blood lymphocytes: a new link between immunity and iron metabolism

Ceruloplasmin (CP) is a multicopper oxidase involved in the acute phase reaction to stress. Although the physiological role of CP is uncertain, its role in iron (Fe) homeostasis and protection against free radical-initiated cell injury has been widely documented. Previous studies showed the existence of two molecular isoforms of CP: secreted CP (sCP) and a membrane glycosylphosphatidylinositol (GPI)-anchored form of CP (GPI-CP). sCP is produced mainly by the liver and is abundant in human serum whereas GPI-CP is expressed in mammalian astrocytes, rat leptomeningeal cells, and Sertolli cells. Herein, we show using RT-PCR that human peripheral blood lymphocytes (huPBL) constitutively express the transcripts for both CP molecular isoforms previously reported. Also, expression of CP in huPBL is demonstrated by immunofluorescence with confocal microscopy and flow cytometry analysis using cells isolated from healthy blood donors with normal Fe status. Importantly, the results obtained show that natural killer cells have a significantly higher CP expression compared to all other major lymphocyte subsets. In this context, the involvement of lymphocyte-derived CP on host defense processes via its anti/prooxidant properties is proposed, giving further support for a close functional interaction between the immune system and the Fe metabolism.

Iron overload and immunity

Progress in the characterization of genes involved in the control of iron homeostasis in humans and in mice has improved the definition of iron overload and of the cells affected by it. The cell involved in iron overload with the greatest effect on immunity is the macrophage. Intriguing evidence has emerged, however, in the last 12 years indicating that parenchymal iron overload is linked to genes classically associated with the immune system. This review offers an update of the genes and proteins relevant to iron metabolism expressed in cells of the innate immune system, and addresses the question of how this system is affected in clinical situations of iron overload. The relationship between iron and the major cells of adaptive immunity, the T lymphocytes, will also be reviewed. Most studies addressing this last question in humans were performed in the clinical model of Hereditary Hemochromatosis. Data will also be reviewed demonstrating how the disruption of molecules essentially involved in adaptive immune responses result in the spontaneous development of iron overload and how they act as modifiers of iron overload.

Comparative study between Hfe-/- and beta2m-/- mice: progression with age of iron status and liver pathology

Hepatic iron overload in hemochomatosis patients can be highly variable but in general it develops in older patients. The purpose of this study was to compare development of iron load in of beta2m-/- and Hfe-/- mice paying special attention to liver pathology in older age groups. Liver iron content of beta2m-/-, Hfe-/- and control B6 mice of different ages (varying from 3 weeks to 18 months) was examined. Additional parameters (haematology indices, histopathology, lipid content and ferritin expression) were also studied in 18-month-old mice. The beta2m-/- strain presents higher hepatic iron content, hepatocyte nuclear iron inclusions, mitochondria abnormalities. In addition, hepatic steatosis was a common observation in this strain. In the liver of Hfe-/- mice, large mononuclear infiltrates positive for ferritin staining were commonly observed. The steatosis commonly observed the beta2m-/- mice may be a reflection of its higher hepatic iron content. The large hepatic mononuclear cell infiltrates seen in Hfe-/- stained for ferritin, may point to the iron sequestration capacity of lymphocytes and contribute to the clarification of the differences found in the progression of hepatic iron overload and steatosis in older animals from the two strains.

The CD8+ T-lymphocyte profile as a modifier of iron overload in HFE hemochromatosis: an update of clinical and immunological data from 70 C282Y homozygous subjects

Hereditary hemochromatosis (HH) is a clinically heterogeneous disease. Among other factors, the individual immunological profile of CD8+ T-lymphocytes has been described to influence the severity of iron overload, with low numbers being negatively correlated with the total amount of body iron stored. With the objective of testing the modifier effect of the individual CD8+ T-lymphocyte profile on the levels of iron stores with age in HH, we reviewed the clinical and immunological data from a group of well-characterized C282Y homozygous HH subjects, regularly followed-up for a period of 20 years. A total of 70 subjects were analyzed. Sixty-four were adults (> or = 18 years): 42 males (mean age 47 +/- 14; range 22-75 years) and 22 females (mean age 46 +/- 14; range 19-65 years). Six were younger than 18 years, 5 males (mean age 9 +/- 4; range 5-14 years) and 1 female (15 years). The characterization of subjects included measurements, at diagnosis, of the iron parameters, transferrin saturation (TfSat) and serum ferritin, quantification of total body iron stores (TBIS) removed by phlebotomies, presence of associated clinical manifestations, and the T-cell immunophenotype (CD4+ and CD8+ T-lymphocytes) determined by flow cytometry. In general, statistically significant lower values of TfSat (67 +/- 17% vs. 89 +/- 14%, P = 0.0006) and ferritin levels (58 +/- 9 vs. 949 +/- 233 ng/ml, P = 0.02) were found in the young subjects in comparison to adults. After the age of 18, however, no further effect of age was significantly found on the biochemical iron parameters either in males or females. A modifier effect of the individual CD8+ T-lymphocyte profile on the association between iron stores and age was demonstrated by multiple regression analysis, where a significant correlation between TBIS and age was found only in males with low (< or = 0.41 x 10(6)/ml) CD8+ T-cell numbers (R2 = 0.43, P < 0.0001). In conclusion, in the present population of C282Y homozygous subjects, the CD8+ T-lymphocyte profile could be considered a modifier of the iron overload with increasing age in males, with low numbers predicting a severe outcome.

Immune-mediated liver injury: prognostic value of CD4+, CD8+, and CD68+ in infants with extrahepatic biliary atresia

BACKGROUND

Hepatic fibrosis and cirrhosis develop progressively in extrahepatic biliary atresia (EHBA) despite timely surgical intervention.

PURPOSE

The aim of the study was to define CD4+ helper T lymphocytes, cytotoxic CD8+ T lymphocytes, and CD68+ (macrophages) infiltration of portal tracts and lobules and hepatic fibrosis as possible predictive measures of outcome of infants having EHBA.

METHODS

The outcome of 32 infants with EHBA was correlated to their percutaneous biopsy and postportoenterostomy core liver tissue infiltration by CD4+, CD68+, and CD8+ cells and to the degree of detected fibrosis.

RESULTS

Portoenterostomy cores were heavily infiltrated by CD4+, CD8+, and CD68+, compared with the preoperative liver biopsy (P = .008, .004, and .017, respectively). Infants having favorable outcome had more macrophage infiltration in portoenterostomy core compared with those having an unfavorable outcome (25.66 +/- 29.77 per HPF compared with 11.62 +/- 4.58, P = .000). Mean CD4+/CD8+ ratio was 1.54 +/- 1.37 in those who died within 18 months postoperatively and 0.733 +/- 0.48 in others (P = .021).

CONCLUSION

Immune-mediated destruction of portal tracts is an integral part of pathogenesis of EHBA.

Contribution of Hfe expression in macrophages to the regulation of hepatic hepcidin levels and iron loading

Hereditary hemochromatosis (HH), an iron overload disease associated with mutations in the HFE gene, is characterized by increased intestinal iron absorption and consequent deposition of excess iron, primarily in the liver. Patients with HH and Hfe-deficient (Hfe-/-) mice manifest inappropriate expression of the iron absorption regulator hepcidin, a peptide hormone produced by the liver in response to iron loading. In this study, we investigated the contribution of Hfe expression in macrophages to the regulation of liver hepcidin levels and iron loading. We used bone marrow transplantation to generate wild-type (wt) and Hfe-/- mice chimeric for macrophage Hfe gene expression. Reconstitution of Hfe-deficient mice with wt bone marrow resulted in augmented capacity of the spleen to store iron and in significantly decreased liver iron loading, accompanied by a significant increase of hepatic hepcidin mRNA levels. Conversely, wt mice reconstituted with Hfe-deficient bone marrow had a diminished capacity to store iron in the spleen but no significant alterations of liver iron stores or hepcidin mRNA levels. Our results suggest that macrophage Hfe participates in the regulation of splenic and liver iron concentrations and liver hepcidin expression.

Molecular analysis of iron overload in beta2-microglobulin-deficient mice

Beta2-microglobulin knockout (beta2m-/-) mice represent an instructive model of spontaneous iron overload resembling genetic hemochromatosis. The mechanism of iron accumulation in this mouse model may be more complex than involving the MHC class I-like protein HFE. We report that beta2m-deficient mice, like Hfe-/- mice, lack the adaptive hepatic hepcidin mRNA increase to iron overload. The inverse correlation of hepatic iron levels and hepcidin mRNA expression in six beta2m-/- mice underlines the importance of hepcidin in regulating body iron stores. In contrast to Hfe-/- mice, beta2m-deficient mice display increased expression of the duodenal iron transporters DMT1 and ferroportin 1. This result implicates a broader role of beta2m in mammalian iron metabolism, suggesting that (an) additional beta2m-interacting protein(s) could be involved in controlling iron homeostasis, and highlighting the emerging connection of iron metabolism with the immune system.

Altered expression of CD1d molecules and lipid accumulation in the human hepatoma cell line HepG2 after iron loading

Iron overload in the liver may occur in clinical conditions such as hemochromatosis and nonalcoholic steatohepatitis, and may lead to the deterioration of the normal liver architecture by mechanisms not well understood. Although a relationship between the expression of ICAM-1, and classical major histocompatibility complex (MHC) class I molecules, and iron overload has been reported, no relationship has been identified between iron overload and the expression of unconventional MHC class I molecules. Herein, we report that parameters of iron metabolism were regulated in a coordinated-fashion in a human hepatoma cell line (HepG2 cells) after iron loading, leading to increased cellular oxidative stress and growth retardation. Iron loading of HepG2 cells resulted in increased expression of Nor3.2-reactive CD1d molecules at the plasma membrane. Expression of classical MHC class I and II molecules, ICAM-1 and the epithelial CD8 ligand, gp180 was not significantly affected by iron. Considering that intracellular lipids regulate expression of CD1d at the cell surface, we examined parameters of lipid metabolism in iron-loaded HepG2 cells. Interestingly, increased expression of CD1d molecules by iron-loaded HepG2 cells was associated with increased phosphatidylserine expression in the outer leaflet of the plasma membrane and the presence of many intracellular lipid droplets. These data describe a new relationship between iron loading, lipid accumulation and altered expression of CD1d, an unconventional MHC class I molecule reported to monitor intracellular and plasma membrane lipid metabolism, in the human hepatoma cell line HepG2.

Involvement of the major histocompatibility complex region in the genetic regulation of circulating CD8 T-cell numbers in humans

Variability in T-lymphocyte numbers is partially explained by a genetic regulation. From studies in animal models, it is known that the Major Histocompatibility Complex (MHC) is involved in this regulation. In humans, this has not been shown yet. The objective of the present study was to test the hypothesis that genes in the MHC region influence the regulation of T-lymphocyte numbers. Two approaches were used. Association studies between T-cell counts (CD4(+) and CD8(+)) or total lymphocyte counts and HLA class I alleles (A and B) or mutations in the HFE (C282Y and H63D), the hemochromatosis gene, in an unrelated population (n = 264). A second approach was a sibpair correlation analysis of the same T-cell counts in relation to HLA-HFE haplotypes in subjects belonging to 48 hemochromatosis families (n = 456 sibpairs). In the normal population, results showed a strong statistically significant association of the HLA-A*01 with high numbers of CD8(+) T cells and a less powerful association with the HLA-A*24 with low numbers of CD8(+) T cells. Sibpair correlations revealed the most significant correlation for CD8(+) T-cell numbers for sibpairs with HLA-HFE-identical haplotypes. This was not observed for CD4(+) T cells. These results show that the MHC region is involved in the genetic regulation of CD8(+) T-cell numbers in humans. Identification of genes responsible for this control may have important biological and clinical implications.

The non-classical HLA class I molecule HFE does not influence the NK-like activity contained in fresh human PBMCs and does not interact with NK cells

In humans, four beta2-microglobulin-associated non-classical class I molecules are encoded in the MHC: HLA-E, -F, -G and -H. Three of them (HLA-E, -F and -G) were shown to inhibit NK activity. On the contrary, the fourth one, HLA-H, named HFE after it was found to be mutated in patients suffering from inherited hemochromatosis, has been shown to be involved only in the regulation of iron uptake. We tested the capacity of HFE to affect (enhance or reduce) specifically the NK activity contained in non-manipulated fresh human PBMCs. We showed that HFE expression by target cells does not affect their killing by the NK-like activity contained in PBMCs. Moreover, using fluorescent HFE tetramers, we could confirm that blood NK cells as well as blood gammadelta T cells do not bind HFE. Altogether, our data indicate that HFE does not affect the NK activity contained in the PBMCs.

Contributions of beta2-microglobulin-dependent molecules and lymphocytes to iron regulation: insights from HfeRag1(-/-) and beta2mRag1(-/-) double knock-out mice

Genetic causes of hereditary hemochromatosis (HH) include mutations in the HFE gene, coding for a beta2-microglobulin (beta2m)-associated major histocompatibility complex class I-like protein. However, iron accumulation in patients with HH can be highly variable. Previously, analysis of beta2mRag1(-/-) double-deficient mice, lacking all beta2m-dependent molecules and lymphocytes, demonstrated increased iron accumulation in the pancreas and heart compared with beta2m single knock-out mice. To evaluate whether the observed phenotype in beta2mRag1(-/-) mice was due solely to the absence of Hfe or to other beta2m-dependent molecules, we generated HfeRag1(-/-) double-deficient mice. Our studies revealed that introduction of Rag1 deficiency in Hfe knock-out mice leads to heightened iron overload, mainly in the liver, whereas the heart and pancreas are relatively spared compared with beta2mRag1(-/-) mice. These results suggest that other beta2m-interacting protein(s) may be involved in iron regulation and that in the absence of functional Hfe molecules lymphocyte numbers may influence iron overload severity.

HFE, the MHC and hemochromatosis: paradigm for an extended function for MHC class I

HFE was discovered as the hereditary hemochromatosis (HH) gene. It is located on chromosome 6 (6p21.3), 4Mb telomeric to the HLA-A locus, and its product has a structure similar to MHC class I molecules. HFE encodes two frequent mutations: C282Y and H63D. One of these (C282Y) is present in a large proportion of Caucasian HH patients. HFE has a tissue distribution compatible with a role in iron absorption (intestine), recycling (macrophages) and transport to the fetus (placenta).

Evidence for a sub-morphological inflammatory process in the liver in haemochromatosis

BACKGROUND/AIMS

The role of cytokines in hepatic injury has been examined for many liver diseases however little is known of the cytokine involvement in haemochromatosis. The aim of the current study was to examine the hepatic gene expression of potential proinflammatory and profibrogenic cytokines in haemochromatosis.

METHODS

Interferon-gamma, interleukin-10, transforming growth factor-beta(1) and tumor necrosis factor-alpha mRNA expression was assessed in liver tissue from 20 haemochromatosis patients, eight controls and eight chronic hepatitis C patients. To assess the immunophenotype of the inflammatory infiltrate in haemochromatosis, liver sections were subjected to immunohistochemistry using markers for macrophages (CD68, HAM56, MAC387) or T cells (CD3 and CD45RO).

RESULTS

Interferon-gamma mRNA was increased in both haemochromatosis (0.29+/-0.08%, P=0.01) and hepatitis C patients (1.02+/-0.32%, P=0.03) compared to controls (0.04+/-0.01%). Interleukin-10 mRNA was significantly decreased in both haemochromatosis and hepatitis C patients (0.01+/-0.003%, P=0.008 and 0.03+/-0.015%, P=0.02, respectively) compared to controls (0.12+/-0.01%). CD3 positive T-cell number was significantly correlated with increasing hepatic iron concentration (r=0.56, P=0.03).

CONCLUSIONS

This study has demonstrated a distinct pattern of cytokine gene expression in haemochromatosis, which resembles that of inflammatory conditions such as chronic hepatitis C. These factors may play a role in the development of iron-induced hepatic fibrosis in haemochromatosis.

The role of iron in T cell development and autoimmunity

Iron is a vital metal for the proliferation of all cells including those of the immune system. Iron deficiency causes several defects in both the humoral and cellular arms of immunity. One of the most profound changes is a reduction in peripheral T cells and atrophy of the thymus. The presence of transferrin receptor on immature, proliferating thymocytes and the inhibition of thymocyte proliferation and differentiation by anti-transferrin receptor antibody highlight the importance of iron to T cell development. Growing evidence suggests that T cells may in turn, regulate iron metabolism perhaps through interactions with the non-classical major histocompatibility complex gene HFE. The association of the iron transporter NRAMP1 with several autoimmune disorders along with evidence that iron can catalyze the production of cryptic epitopes of several autoantigens, establishes a potential role for iron in the development of autoimmunity.

Peripheral lymphocytes and intracellular cytokines in C282Y homozygous hemochromatosis patients

BACKGROUND/AIMS

Several abnormalities in the immune status of hereditary hemochromatosis patients have been reported. We evaluated the peripheral blood lymphocytes phenotype and cytokine profile of CD8(+) and CD4(+) T cells in C282Y homozygous hereditary hemochromatosis patients compared to control subjects.

METHODS

Peripheral blood lymphocytes from 17 asymptomatic patients and 14 control subjects were analyzed. We determined the distribution of lymphocyte subsets and investigated at single-cell level by flow-cytometry the potential of cytokines production. The frequency of cytokine (interferon gamma, tumor necrosis factor alpha, interleukin 2 (IL-2), IL-4, IL-5, IL-10 and IL-13) producing cells was assessed in total T-lymphocytes, CD3(+)CD8(+) and CD3(+)CD4(+) subsets.

RESULTS

The patients studied showed a significant decrease of total lymphocyte count, T CD4(+)CD3(+), CD28(+), CD8(+)CD28(+) lymphocytes and natural killer (NK) CD56(+)CD16(+)CD3(-) cells. The reduction of CD28(+) and CD8(+)CD28(+) lymphocyte count was inversely related to transferrin saturation index. An increase in the ability of T-cells to produce all the cytokines studied and a major increase in IL-4 and IL-10 production in the CD3(+)CD8(+) subset was found. Our results demonstrate that activated Th1 and Th2 lymphocytes coexist in the peripheral blood of hereditary hemochromatosis patients and that T-cytotoxic (Tc) 2 subset is more expanded than in control population.

CONCLUSIONS

The association of a decreased number of T CD8(+) cytotoxic lymphocytes and NK cells, and the development of Tc2 cells in asymptomatic C282Y homozygous patients represents an imbalance in their immune function that might contribute to the high incidence of hepatocarcinoma.

CD8+CD28- T cells: certainties and uncertainties of a prevalent human T-cell subset

Human peripheral blood CD8+ T cells comprise cells that are in different states of differentiation and under the control of complex homeostatic processes. In a number of situations ranging from chronic inflammatory conditions and infectious diseases to ageing, immunodeficiency, iron overload and heavy alcohol intake, major phenotypic changes, usually associated with an increase in CD8+ T cells lacking CD28 expression, take place. CD8+CD28- T cells are characterized by a low proliferative capacity to conventional stimulation in vitro and by morphological and functional features of activated/memory T cells. Although the nature of the signals that give origin to this T-cell subset is uncertain, growing evidence argues for the existence of an interplay between epithelial cells, molecules with the MHC-class I fold and CD8+ T cells. The possibility that the generation of CD8+CD28- T cells is the combination of TCR/CD3zeta- and regulatory factor-mediated signals as a result of the sensing of modifications of the internal environment is discussed.

Clinical and genetic heterogeneity in hereditary haemochromatosis: association between lymphocyte counts and expression of iron overload

To identify a new marker of expression of disease, independent of HFE genotype in patients with hereditary haemochromatosis (HHC), the total peripheral blood lymphocyte counts were analysed according to iron status in two groups of subjects with HFE mutations. The groups consisted of 38 homozygotes for C282Y, and 107 heterozygotes for the C282Y or compound heterozygotes for C282Y and H63D. For control purposes, total lymphocyte counts and iron status were also examined in 20 index patients with African dietary iron overload, a condition not associated with HFE mutations, and in 144 members of their families and communities. Mean lymphocyte numbers were lower in C282Y homozygous HHC index subjects with cirrhosis and higher iron stores than in those without cirrhosis and with lower iron burdens [(1.65 +/- 0.43) x 10(6)/mL vs. (2.27 +/- 0.49) x 10(6)/mL; p = 0.008]. Similarly, mean lymphocyte counts were significantly lower in C282Y heterozygotes and C282Y/H63D compound heterozygotes with iron overload and increased serum ferritin concentrations compared to those with normal serum ferritin concentrations (p < 0.05). Statistically significant negative correlations were found, in males, between lymphocyte counts and the total body iron stores, either in C282Y homozygous HHC patients (p = 0.031 in a multiple regression model dependent on age) and in C282Y heterozygotes or C282Y/H63D compound heterozygotes with iron overload (p = 0.029 in a simple linear model). In contrast, lymphocyte counts increased with increasing serum ferritin concentrations among the index subjects with African iron overload (r = 0.324, not statistically significant) and among the members of their families and communities (r = 0.170, p = 0.042). These results suggest that a lower peripheral blood lymphocyte count is associated with a greater degree of iron loading in HFE haemochromatosis but not in African iron overload, and they support the notion that the lymphocyte count may serve as a marker of a non-HFE gene that influences the clinical expression of HFE haemochromatosis.