Ferritin synthesis by human T lymphocytes

Proteomic study on the lymphocytes from pregnant Wistar rat females treated with immunosuppressive regimen

Kidney transplantation remains the therapeutic option for patients with end-stage kidney disease. Current immunosuppressive regimens are efficient in combating acute kidney rejection. However, insights into chronic kidney allograft injury remains limited. Simultaneously, pregnancy is more common after kidney transplantation than during dialysis treatment. Due to ethical issues, comprehensive studies on the impact of immunosuppressive regimens on pregnancy are challenging. The study aimed to investigate the proteomic status of lymphocytes obtained from pregnant female rats under immunosuppressive treatment. The experiment involved a group of 10 female, pregnant Wistar rats, five of which were treated with tacrolimus, mofetil mycophenolate, and glucocorticosteroids; five were used as control. The lymphocytes were obtained and analyzed with mass spectrometry. Measurements were processed by a database search in the ProteinPilot software with a cutoff of 1% false discovery rate. The outcomes were verified statistically by a t-test (p value < 0.05) regarding proteins up- and downregulation. A total of 2082 proteins were identified in all experiments. Eight hundred five proteins were quantified in an absolute manner in a data-independent acquisition-total protein approach analysis. Ninety-five proteins were recognized as present at different concentrations in analyzed groups and were annotated to intracellular pathways. The proteins involved in nonsense-mediated decay and L13a-mediated translational silencing of ceruloplasmin expression were recognized as downregulated. The set of proteins clinically identified as acute phase proteins was upregulated. Despite the blockade of adaptive cellular immunity, the lymphocytes in the analyzed group reveal sustained proinflammatory status with decreased ability to regulate translation. This potentially affects pregnancy and immunity.

Ferroptosis: A New Development Trend in Periodontitis

Periodontitis is a chronic inflammatory disease associated with bacterial biofilm. It is characterized by loss of periodontal support tissue and has long been considered as a "silent disease". Because it is difficult to prevent and has a health impact that can not be ignored, researchers have been focusing on a mechanism-based treatment model. Ferroptosis is an iron-dependent regulatory form of cell death, that directly or indirectly affects glutathione peroxidase through different signaling pathways, resulting in a decrease in cell antioxidant capacity, accumulation of reactive oxygen species and lipid peroxidation, which cause oxidative cell death and tissue damage. Recently, some studies have proven that iron overload, oxidative stress, and lipid peroxidation exist in the process of periodontitis. Based on this, this article reviews the relationship between periodontitis and ferroptosis, in order to provide a theoretical reference for future research on the prevention and treatment of periodontal disease.

Iron Metabolism in the Tumor Microenvironment-Implications for Anti-Cancer Immune Response

New insights into the field of iron metabolism within the tumor microenvironment have been uncovered in recent years. Iron promotes the production of reactive oxygen species, which may either trigger ferroptosis cell death or contribute to malignant transformation. Once transformed, cancer cells divert tumor-infiltrating immune cells to satisfy their iron demand, thus affecting the tumor immunosurveillance. In this review, we highlight how the bioavailability of this metal shapes complex metabolic pathways within the tumor microenvironment and how this affects both tumor-associated macrophages and tumor-infiltrating lymphocytes functions. Furthermore, we discuss the potentials as well as the current clinical controversies surrounding the use of iron metabolism as a target for new anticancer treatments in two opposed conditions: i) the "hot" tumors, which are usually enriched in immune cells infiltration and are extremely rich in iron availability within the microenvironment, and ii) the "cold" tumors, which are often very poor in immune cells, mainly due to immune exclusion.

Cell-type-specific insights into iron regulatory processes

Despite its essential role in many biological processes, iron is toxic when in excess due to its propensity to generate reactive oxygen species. To prevent diseases associated with iron deficiency or iron loading, iron homeostasis must be tightly controlled. Intracellular iron content is regulated by the Iron Regulatory Element-Iron Regulatory Protein (IRE-IRP) system, whereas systemic iron availability is adjusted to body iron needs chiefly by the hepcidin-ferroportin (FPN) axis. Here, we aimed to review advances in the field that shed light on cell-type-specific regulatory mechanisms that control or modify systemic and local iron balance, and how shifts in cellular iron levels may affect specialized cell functions.

Transferrin 1 Functions in Iron Trafficking and Genetically Interacts with Ferritin in Drosophila melanogaster

Iron metabolism is an essential process that when dysregulated causes disease. Mammalian serum transferrin (TF) plays a primary role in delivering iron to cells. To improve our understanding of the conservation of iron metabolism between species, we investigate here the function of the TF homolog in Drosophila melanogaster, transferrin 1 (Tsf1). Tsf1 knockdown results in iron accumulation in the gut and iron deficiency in the fat body (which is analogous to the mammalian liver). Fat body-derived Tsf1 localizes to the gut surface, suggesting that Tsf1 functions in trafficking iron between the gut and the fat body, similar to TF in mammals. Moreover, Tsf1 knockdown strongly suppresses the phenotypic effects of ferritin (Fer1HCH) RNAi, an established iron trafficker in Drosophila. We propose that Tsf1 and ferritin compete for iron in the Drosophila intestine and demonstrate the value of using Drosophila for investigating iron trafficking and the evolution of systemic iron regulation.

Cutting Edge: Activation-Induced Iron Flux Controls CD4 T Cell Proliferation by Promoting Proper IL-2R Signaling and Mitochondrial Function

Iron has long been established as a critical mediator of T cell development and proliferation. However, the mechanisms by which iron controls CD4 T cell activation and expansion remain poorly understood. In this study, we show that stimulation of CD4 T cells from C57BL/6 mice not only decreases total and labile iron levels but also leads to changes in the expression of iron homeostatic machinery. Additionally, restraining iron availability in vitro severely inhibited CD4 T cell proliferation and cell cycle progression. Although modulating cellular iron levels increased IL-2 production by activated T lymphocytes, CD25 expression and pSTAT5 levels were decreased, indicating that iron is necessary for IL-2R-mediated signaling. We also found that iron deprivation during T cell stimulation negatively impacts mitochondrial function, which can be reversed by iron supplementation. In all, we show that iron contributes to activation-induced T cell expansion by positively regulating IL-2R signaling and mitochondrial function.

Up-regulated ferritin in periodontitis promotes inflammatory cytokine expression in human periodontal ligament cells through transferrin receptor via ERK/P38 MAPK pathways

OBJECTIVE

Ferritin, an iron-binding protein, is ubiquitous and highly conserved; it plays a crucial role in inflammation, which is the main symptom of periodontitis. Full-length cDNA library analyses have demonstrated abundant expression of ferritin in human periodontal ligament. The aims of the present study were to explore how ferritin is regulated by local inflammation, and to investigate its functions and mechanisms of action in the process of periodontitis.

METHODS

Human gingival tissues were collected from periodontitis patients and healthy individuals. Experimental periodontitis was induced by ligature of second molars in mice. The expression of ferritin light polypeptide (FTL) and ferritin heavy polypeptide (FTH) were assessed by immunohistochemistry. Meanwhile, after stimulating human periodontal ligament cells (HPDLCs) with P. gingivalis-lipopolysaccharide (LPS), interleukin (IL)-6, and tumor necrosis factor-α (TNF-α), the expression of FTH and FTL were measured. Then, IL-6 and IL-8 were measured after incubation with different concentrations of apoferritin (iron-free ferritin) and several intracellular signaling pathway inhibitors, or after knockdown of the transferrin receptor.

RESULTS

Both FTH and FTL were substantially higher in inflamed periodontal tissues than in healthy tissues. The location of the elevated expression correlated well with the extent of inflammatory infiltration. Moreover, expression of FTH and FTL were enhanced after stimulation with P. gingivalis-LPS, IL-6, TNF-α. Apoferritin induced the production of IL-6 and IL-8 in a dose-dependent manner partly through binding to the transferrin receptor and activating ERK/P38 signaling pathways in HPDLCs.

CONCLUSIONS

Ferritin is up-regulated by inflammation and exhibits cytokine-like activity in HPDLCs inducing a signaling cascade that promotes expression of pro-inflammatory cytokines associated with periodontitis.

Iron in the Tumor Microenvironment-Connecting the Dots

Iron metabolism and tumor biology are intimately linked. Iron facilitates the production of oxygen radicals, which may either result in iron-induced cell death, ferroptosis, or contribute to mutagenicity and malignant transformation. Once transformed, malignant cells require high amounts of iron for proliferation. In addition, iron has multiple regulatory effects on the immune system, thus affecting tumor surveillance by immune cells. For these reasons, inconsiderate iron supplementation in cancer patients has the potential of worsening disease course and outcome. On the other hand, chronic immune activation in the setting of malignancy alters systemic iron homeostasis and directs iron fluxes into myeloid cells. While this response aims at withdrawing iron from tumor cells, it may impair the effector functions of tumor-associated macrophages and will result in iron-restricted erythropoiesis and the development of anemia, subsequently. This review summarizes our current knowledge of the interconnections of iron homeostasis with cancer biology, discusses current clinical controversies in the treatment of anemia of cancer and focuses on the potential roles of iron in the solid tumor microenvironment, also speculating on yet unknown molecular mechanisms.

Quantitative susceptibility mapping and 23 Na imaging-based in vitro characterization of blood clotting kinetics

Blood clotting is a fundamental biochemical process in post-hemorrhagic hemostasis. Although the varying appearance of coagulating blood in T₁ - and T₂ -weighted images is widely used to qualitatively determine bleeding age, the technique permits only a rough discrimination of coagulation stages, and it remains difficult to distinguish acute and chronic hemorrhagic stages because of low T₁ - and T₂ -weighted signal intensities in both instances. To investigate new biomedical parameters for magnetic resonance imaging-based characterization of blood clotting kinetics, sodium imaging and quantitative susceptibility mapping (QSM) were compared with conventional T₁ - and T₂ -weighted imaging, as well as with biochemical hemolysis parameters. For this purpose, a blood-filled spherical agar phantom was investigated daily for 14 days, as well as after 24 days at 7 T after initial preparation with fresh blood. T₁ - and T₂ -weighted sequences, a three-dimensional (3D) gradient echo sequence and a density-adapted 3D radial projection reconstruction pulse sequence for ²³ Na imaging were applied. For hemolysis estimations, free hemoglobin and free potassium concentrations were measured photometrically and with the direct ion-selective electrode method, respectively, in separate heparinized whole-blood samples along the same timeline. Initial mean susceptibility was low (0.154 ± 0.020 ppm) and increased steadily during the course of coagulation to reach up to 0.570 ± 0.165 ppm. The highest total sodium (NaT) values (1.02 ± 0.06 arbitrary units) in the clot were observed initially, dropped to 0.69 ± 0.13 arbitrary units after one day and increased again to initial values. Compartmentalized sodium (NaS) showed a similar signal evolution, and the NaS/NaT ratio steadily increased over clot evolution. QSM depicts clot evolution in vitro as a process associated with hemoglobin accumulation and transformation, and enables the differentiation of the acute and chronic coagulation stages. Sodium imaging visualizes clotting independent of susceptibility and seems to correspond to clot integrity. A combination of QSM and sodium imaging may enhance the characterization of hemorrhage.

Measurement of Ferritin-Bearing Lymphocytes in Man. Preliminary Studies on the Use of Monoclonal Antibodies Specific for the L and H Subunits of Ferritin

We used the monoclonal antibodies LFO3 (specific for the L subunit of ferritin) and 2A4 (specific for the H subunit) in an indirect immunofluorescence test for enumerating ferritin-bearing lymphocytes (FBL). In 13 normal subjects, the geometric mean value of FBL was 4 % (range 0–13 %) with the monoclonal antibody LFO3, and 3 % (range 0–8 %) with the monoclonal antibody 2A4. Values in 5 subjects with transfusional iron overload and increased plasma L-type ferritin concentration were 5 % (4–7 %) and 3 % (2–4 %), respectively, which is similar to those in normal subjects. Thirteen patients with malignant disease had normal to increased values for plasma ferritin; the circulating protein was largely of L-type with undetectable or very low concentrations of H-type ferritin. In the same patients, the percentage of FBL was greater with the monoclonal antibody 2A4 (geometric mean value 8 %; range 3–12 %) than with the monoclonal antibody LFO3 (geometric mean value 3 %; range, 1–7 %). It is concluded that acidic and basic isoferritins can be differently expressed on the surface of peripheral blood lymphocytes, and that the monoclonal 2A4 could be particularly useful in the measurement of FBL in patients with malignancy.

Immunological Reactivity of Serum Ferritin in Patients with Malignancy

Serum ferritin has been suggested as a tumor marker in the diagnosis of certain malignancies and for following the activity or dissemination of the malignant process. Since neoplastic tissues generally contain more acidic isoferritins than their normal tissue counterparts, it has also been suggested that the specific assay of such isoferritins in serum may be of particular value in the diagnosis of malignancy. In this work, we have evaluated ferritin concentration in the serum of normal subjects and patients with acute nonlymphocytic leukemia, Hodgkin's disease, breast cancer and lung cancer by simultaneously using three different immunoassays: an immunoradiometric assay based on polyclonal antibodies against human liver (basic, L-subunit rich) ferritin, a radioimmunoassay based on polyclonad antibodies against HeLa cell (acidic, H-subunit rich) ferritin, and an immunoradiometric assay based on the monoclonal antibody 2A4 raised against human heart (acidic, H-subunit rich) ferritin. Most of the patients studied had increased values for liver-type ferritin in the absence of increased iron stores. Binding of serum ferritin to concanavalin A did not prove to be useful in distinguishing a tumor-specific basic isoferritin. The HeLa ferritin assay was found to be less specific than the heart ferritin assay in the detection of acidic isoferritins, and did not provide any advantage over the liver assay in detecting the increased levels of serum ferritin associated with malignant disease. Heart-type ferritin was found in one-fifth of normal sera and 64% of sera from patients with malignancy. Values were very low compared with those for basic ferritin, ranging from less than 0.1 to 17% of total serum ferritin (geometric mean value 1.3%) in patients with malignancy. These findings indicate that at present there is little application for serum ferritin immunoassays based on antibodies to HeLa cell or heart ferritin in the diagnosis or monitoring of malignant disease. This seems to be due to the presence in human serum of biding factors which are responsible for the rapid clearance of acidic isoferritins from the circulation. The serum concentration of basic ferritin, however, can be useful in the diagnosis and management of some malignancies, and it is possible that studies on cell isoferritins can be important in biologic monitoring of neoplastic disorders. It should also be noted that the increased levels of serum ferritin found in patients with malignancy can exert adverse effects on the host immune response and perhaps an inhibitory effect on hematopoiesis.

Unexplained isolated hyperferritinemia without iron overload

Although hyperferritinemia may be reflective of elevated total body iron stores, there are conditions in which ferritin levels are disproportionately elevated relative to iron status. Autosomal dominant forms of hyperferritinemia due to mutations in the L-ferritin IRE or in A helix of L-ferritin gene have been described, however cases of isolated hyperferritinemia still remain unsolved. We describe 12 Italian subjects with unexplained isolated hyperferritinemia (UIH). Four probands have affected siblings, but no affected parents or offspring. Sequencing analyses did not identify casual mutations in ferritin gene or IRE regions. These patients had normal levels of intracellular ferritin protein and mRNA in peripheral blood cells excluding pathological ferritin production at transcriptional and post-transcriptional level. In contrast with individuals with benign hyperferritinemia caused by mutations affecting the ferritin A helix, low rather than high glycosylation of serum ferritin was observed in our UIH subjects compared with controls. These findings suggest that subjects with UIH have a previously undescribed form of hyperferritinemia possibly attributable to increased cellular ferritin secretion and/or decreased serum ferritin clearance. The cause remains to be defined and we can only speculate the existence of mutations in gene/s not directly implicated in iron metabolism that could affect ferritin turnover including ferritin secretion.

Intracellular Iron Chelation Modulates the Macrophage Iron Phenotype with Consequences on Tumor Progression

A growing body of evidence suggests that macrophage polarization dictates the expression of iron-regulated genes. Polarization towards iron sequestration depletes the microenvironment, whereby extracellular pathogen growth is limited and inflammation is fostered. In contrast, iron release contributes to cell proliferation, which is important for tissue regeneration. Moreover, macrophages constitute a major component of the infiltrates in most solid tumors. Considering the pivotal role of macrophages for iron homeostasis and their presence in association with poor clinical prognosis in tumors, we approached the possibility to target macrophages with intracellular iron chelators. Analyzing the expression of iron-regulated genes at mRNA and protein level in primary human macrophages, we found that the iron-release phenotype is a characteristic of polarized macrophages that, in turn, stimulate tumor cell growth and progression. The application of the intracellular iron chelator (TC3-S₎₂ shifted the macrophage phenotype from iron release towards sequestration, as determined by the iron-gene profile and atomic absorption spectroscopy (AAS). Moreover, whereas the addition of macrophage supernatants to tumor cells induced tumor growth and metastatic behavior, the supernatant of chelator-treated macrophages reversed this effect. Iron chelators demonstrated potent anti-neoplastic properties in a number of cancers, both in cell culture and in clinical trials. Our results suggest that iron chelation could affect not only cancer cells but also the tumor microenvironment by altering the iron-release phenotype of tumor-associated macrophages (TAMs). The study of iron chelators in conjunction with the effect of TAMs on tumor growth could lead to an improved understanding of the role of iron in cancer biology and to novel therapeutic avenues for iron chelation approaches.

Local iron homeostasis in the breast ductal carcinoma microenvironment

BACKGROUND

While the deregulation of iron homeostasis in breast epithelial cells is acknowledged, iron-related alterations in stromal inflammatory cells from the tumor microenvironment have not been explored.

METHODS

Immunohistochemistry for hepcidin, ferroportin 1 (FPN1), transferrin receptor 1 (TFR1) and ferritin (FT) was performed in primary breast tissues and axillary lymph nodes in order to dissect the iron-profiles of epithelial cells, lymphocytes and macrophages. Furthermore, breast carcinoma core biopsies frozen in optimum cutting temperature (OCT) compound were subjected to imaging flow cytometry to confirm FPN1 expression in the cell types previously evaluated and determine its cellular localization.

RESULTS

We confirm previous results by showing that breast cancer epithelial cells present an 'iron-utilization phenotype' with an increased expression of hepcidin and TFR1, and decreased expression of FT. On the other hand, lymphocytes and macrophages infiltrating primary tumors and from metastized lymph nodes display an 'iron-donor' phenotype, with increased expression of FPN1 and FT, concomitant with an activation profile reflected by a higher expression of TFR1 and hepcidin. A higher percentage of breast carcinomas, compared to control mastectomy samples, present iron accumulation in stromal inflammatory cells, suggesting that these cells may constitute an effective tissue iron reservoir. Additionally, not only the deregulated expression of iron-related proteins in epithelial cells, but also on lymphocytes and macrophages, are associated with clinicopathological markers of breast cancer poor prognosis, such as negative hormone receptor status and tumor size.

CONCLUSIONS

The present results reinforce the importance of analyzing the tumor microenvironment in breast cancer, extending the contribution of immune cells to local iron homeostasis in the tumor microenvironment context.

Physiological implications of NTBI uptake by T lymphocytes

In iron overload disorders a significant fraction of the total iron circulates in the plasma as low molecular weight complexes not bound to transferrin, known as non-transferrin-bound iron (NTBI). By catalyzing the formation of free radicals, NTBI accumulation results in oxidative stress and cellular damage, being a major cause of organ toxicity. NTBI is rapidly and preferentially cleared from circulation by the liver and the myocardium, the main disease targets in iron overload conditions. We have recently demonstrated that human peripheral blood T lymphocytes take up NTBI in vitro, with a pattern that resembles that of hepatocytes. Since T lymphocytes constitute a numerically important component of the circulating cell pool, these findings support a putative role for this cell type in the systemic protection against iron toxicity. Here we tested the hypothesis that the circulating peripheral blood T lymphocyte pool constitutes an important storage compartment for NTBI and is thus a modifier of NTBI deposition in target organs. First we show that NTBI uptake by human T lymphocytes increases the expression of the iron-storage protein ferritin and of the iron exporter ferroportin via an IRE-dependent mechanism. NTBI retention by T lymphocytes is shown to be critically controlled by the hepcidin-mediated modulation of ferroportin both in vitro and in vivo. Finally, the protective effect of T lymphocytes was tested by analyzing the patterns of iron accumulation in the T lymphocyte-deficient mouse model Foxn1^nu before and after reconstitution with T lymphocytes by adoptive transfer. The results confirmed a significant increase of liver and pancreas iron accumulation in T lymphocyte-deficient mice. NTBI accumulation in the liver and spleen was prevented by reconstitution with syngeneic T lymphocytes. Altogether, our results demonstrate that T lymphocytes are important components of a circulating “NTBI storage compartment” and show its physiological relevance as a modifier of tissue iron overload.

Conditional deletion of ferritin h in mice reduces B and T lymphocyte populations

The immune system and iron availability are intimately linked as appropriate iron supply is needed for cell proliferation, while excess iron, as observed in hemochromatosis, may reduce subsets of lymphocytes. We have tested the effects of a ferritin H gene deletion on lymphocytes. Mx-Cre mediated conditional deletion of ferritin H in bone marrow reduced the number of mature B cells and peripheral T cells in all lymphoid organs. FACS analysis showed an increase in the labile iron pool, enhanced reactive oxygen species formation and mitochondrial depolarization. The findings were confirmed by a B-cell specific deletion using Fth^lox/lox; CD19-Cre mice. Mature B cells were strongly under-represented in bone marrow and spleen of the deleted mice, whereas pre-B and immature B cells were not affected. Bone marrow B cells showed increased proliferation as judged by the number of cells in S and G2/M phase as well as BrdU incorporation. Upon in vitro culture with B-cell activating factor of the tumor necrosis factor family (BAFF), ferritin H-deleted spleen B cells showed lower survival rates than wild type cells. This was partially reversed with iron-chelator deferiprone. The loss of T cells was also confirmed by a T cell-specific deletion in Fth^lox/lox;CD4-Cre mice. Our data show that ferritin H is required for B and T cell survival by actively reducing the labile iron pool. They further suggest that natural B and T cell maturation is influenced by intracellular iron levels and possibly deregulated in iron excess or deprivation.

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.

Strain differences in pleural mesothelial cell reactions induced by potassium octatitanate fibers (TISMO) infused directly into the thoracic cavity

Although we have previously reported that the fiber-shaped TISMO, morphologically similar to asbestos, can induce a severe mesothelial reaction in A/J mice, it is important to clarify any strain differences. In the present study, female A/J, C3H/HeN, ICR and C57BL/6 mice were therefore employed as test strains. At the beginning of the experiment, all mice underwent a left thoracotomy and direct administration of 3mg of TISMO particles suspended in 0.2 ml saline into the left thorax. The experiment was terminated after 21 weeks and all groups were sacrificed and the mesothelium and main organs were examined histopathologically. To contribute to mechanistic analysis, iron staining with Berlin blue and Turnbull's blue, and immunostaining for calretinin were also performed. The present experiment demonstrated only minor strain differences in the degree of pleural reaction to TISMO. However, there was clear variation in the iron and lymphocyte accumulation in the pleura and in the liver. This difference in response to TISMO fibers in vivo is important information when considering the development of mesothelioma as an animal model and the extrapolation to human risk from such animal studies.

The utility of serum hepcidin as a biomarker for late-onset neonatal sepsis

OBJECTIVE

To assess the utility of hepcidin, a potent regulator of host defense and inflammation, in the diagnosis of late-onset sepsis in very low birth weight infants.

STUDY DESIGN

We compared the diagnostic performance of hepcidin with C-reactive protein from the serum concentrations in acute and convalescent blood specimens obtained from 44 infants suspected of late-onset sepsis. The predictive accuracies were assessed from the areas under receiver operating characteristic curves and the cutoffs that differentiated infants with and without sepsis were identified using classification and regression tree analysis.

RESULTS

Seventeen of the enrolled infants in this study were bacteremic and/or received antibiotics for neonatal sepsis for ≥ 5 days (infants with sepsis). The concentrations of hepcidin were increased 4-fold in infants with compared with infants without sepsis (P < .0001) and returned to similar levels following therapy. The areas under receiver operating characteristic curves of hepcidin was 0.93 compared with 0.83 for C-reactive protein, P = .06. Hepcidin concentration >92.2 ng/mL correctly classified 91% of all infants (positive predictive value: 100%, negative predictive value: 87%, specificity: 100%, and sensitivity: 76%).

CONCLUSION

Serum hepcidin concentration may be a useful adjunct test, in addition to blood culture and other markers of infection, in the evaluation of late-onset sepsis in very low birth weight infants.

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.

Macrophage activation syndrome: serological markers and treatment with anti-thymocyte globulin

Two patients presented at the University of Rochester Medical Center with a febrile illness, cytopenias, organ failure (liver failure or respiratory failure), and markedly elevated serum ferritin and sIL-2R. A diagnosis of probable macrophage activation syndrome was made. Both patients failed initial therapy with steroids and cyclosporine, either due to toxicity or lack of efficacy. Both patients responded dramatically to rabbit anti-thymocyte globulin (ATG).

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.

Red blood cells upregulate cytoprotective proteins and the labile iron pool in dividing human T cells despite a reduction in oxidative stress

We have recently reported that red blood cells (RBC) promote T cell growth and survival by inhibiting activation-induced T cell death. In the present study, we have examined parameters of oxidative stress and intracellular iron in activated T cells and correlated these data with the expression of ferritin, heme oxygenase-1 (HO-1), and the transferrin receptor CD71. T cells growing in the presence of RBC had reduced levels of reactive oxygen species (ROS) and oxidatively modified proteins, suggesting that RBC efficiently counteracted ROS production on the activated T cells. Flow cytometry and immunodetection demonstrated that T cells dividing in the presence of RBC had increased levels of intracellular ferritin rich in L-subunits and HO-1 along with a downmodulation in CD71 expression. Finally, using the fluorescent iron indicator calcein and flow cytometry analysis, we were able to show that a relative amount of the labile iron pool (LIP) was upregulated in T cells growing in the presence of RBC. These findings are consistent with a typical response to iron overload. However, neither heme compounds nor ferric iron reproduced the levels of expansion and survival of T cells induced by intact RBC. Altogether, these data suggest that RBC inhibit apoptosis of activated T cells by a combination of ROS scavenging and upregulation of cytoprotective proteins such as ferritin and HO-1, which may counteract a possible toxic effect of the increased intracellular free iron.

Regulated secretion of glycosylated human ferritin from hepatocytes

Serum ferritin has been used widely in clinical medicine chiefly as an indicator of iron stores and inflammation. Circulating ferritin also can have paracrine effects. Despite the clinical significance of serum ferritin, its secretion remains an enigma. The consensus view is that serum ferritin arises from tissue ferritins--principally ferritin light--which can be glycosylated. Ferritin heavy and light chains are cytosolic proteins that form cages of 24 subunits to store intracellular iron. We show that ferritin light is secreted when its expression is increased in stable, transfected HepG2 cells or adenovirus-infected HepG2 cells. Export occurs through the classical secretory pathway and some chains are N-glycosylated. Ferritins do not need to form cages prior to secretion. Secretion is blocked specifically, effectively, and rapidly by a factor in serum. The timing of this inhibition of ferritin secretion suggests that normally cytosolic ferritin L is targeted to the secretory pathway during translation despite the absence of a conventional signal sequence. Thus, secretion of glycosylated and unglycosylated ferritin is a regulated and not a stochastic process.

A role for ferritin in hematopoiesis and the immune system

Elevated serum ferritin levels have been reported in a number of pathological states. These observations indicate that cells of the immune system can participate in the prevention of potential tissue toxicity from iron accumulation, and iron and iron-binding protein have important effects on immune systems. Ferritin is generally regarded as an intracellular iron storage protein. However, small amounts of ferritin circulate in the serum of normal individuals, and the physiological role of serum ferritin remains obscure. Although the function of ferritin is inevitably linked to iron metabolism, a role for ferritin in hematopoiesis and the immune system has drawn attention for years. Ferritin has an inhibitory effect on the in vitro growth of human hematopoietic progenitor cells and on the proliferation of T lymphocytes in vitro. Recently we report that ferritin may directly suppress the differentiation of human B lymphocytes maturing into antibody producing cells in vitro. In the present review, we summarise this field of research.

Ferritin mRNAs on rat liver membrane-bound polysomes synthesize ferritin that does not translocate across membranes

Ferritin is a typical intracellular protein but small amounts are also present in serum and other biological fluids. The source and physiological significance of serum ferritin are still obscure. The presence of ferritin mRNAs on polysomes bound to endoplasmic reticulum (ER) could be relevant for the secretion of ferritin. By Northern blot analysis we found significant amounts of both L and H subunit mRNAs on rat liver membrane-bound polysomes. Immunoprecipitation of translational products of membrane-bound polysomes with anti-rat liver ferritin antibody showed that ferritin is actually synthesized on ER membranes. Analysis of RNA extracted from salt-washed rat liver microsomes demonstrated that ferritin mRNAs are translated by polysomes tightly bound to ER membranes. Following iron treatment, both the amount of H and L subunit mRNAs and ferritin synthesis increased sharply in both free and bound polysomal fractions. Translation of membrane-bound polysomes in the presence of microsomal membranes indicated that ferritin is not processed by signal sequence cleavage or glycosylation and is not translocated into ER membranes. Ferritin mRNAs found on membrane-bound polysomes are associated with ER in a specific way, however, their products do not seem to follow the classic secretory pathway and therefore the significance of the large amount of ferritin mRNAs in the bound ribosome fraction remains unclear.

Expression of isoferritins in peripheral blood lymphocytes: effect of phytohaemagglutinin and iron

This study shows that incubation of lymphocytes in phytohaemagglutinin medium together with iron supplementation leads to an increase of ferritin synthesis concomitant with increased intracellular ferritin concentration especially of heart-type ferritin. Increasing levels of iron do not increase heart-type ferritin concentration further; in contrast, spleen-type ferritin is gradually increased with increasing iron levels. The preferential increase in spleen-type ferritin on growth in iron-enriched medium may be explained by two distinct roles in the metabolism of these two isoferritins. Heart-type isoferritin appears to be involved in more active iron metabolism in lymphocytes whilst the spleen-type isoferritin may function as an intracellular depot of excess iron that is not immediately utilised for metabolic activity.

T-cell mitogenesis stimulates the synthesis of a mRNA species coding for a 43-kDa peptide reactive with CM-H-9, a monoclonal antibody specific for placental isoferritin

In studying the changes that occur in concanavalin A-activated T lymphocytes, an mRNA species was discovered by hybridization of poly(A)+ mRNA with a human ferritin heavy chain cDNA probe. This ferritin mRNA, termed superheavy chain mRNA, differed from the known human ferritin heavy chain mRNAs by its larger size and degree of homology. The superheavy chain mRNA was isolated by sucrose-gradient centrifugation and translated in vitro in a cell-free system. The products obtained included two peptides (superheavy) of 43kDa that reacted with CM-H-9, a monoclonal antibody specific for placental isoferritin. De novo synthesis in intact transformed T cells revealed the synthesis of the superheavy chain peptides that were immunoprecipitated by anti-ferritin monoclonal antibody CM-G-8 and by placental isoferritin specific monoclonal antibody CM-H-9. The above results indicated that blast transformation of human T cells stimulated the appearance of a unique mRNA species that coded for a superheavy chain peptide associated with placental isoferritin, which was not detected in resting T cells.

Ferritin synthesis in peripheral blood lymphocytes following in vitro stimulation

The incubation of normal peripheral blood lymphocytes with phytohaemagglutinin results in an increase in DNA synthesis accompanied by an increase in ferritin synthesis, as determined by 3H-leucine incorporation into ferritin isolated by immunoprecipitation. The increase was 5 to 8 times greater than that of non-stimulated cells. This phenomenon was associated with a 3- to 6-fold increase of intracellular ferritin when compared with the original ferritin concentration. While the significance of increased ferritin expression in proliferative cells is not known, an increase in ferritin synthesis following in vitro stimulation is probably related to increased metabolic activity of the cells.

Iron, iron-binding proteins and immune system cells

In summary, the work reviewed in the present paper indicates that 1. Iron and the iron-binding proteins can act as regulators of immune function, and not only as a result of a nutritional dependence of lymphoid cells on transferrin and transferrin-iron. Subsets of cells of the immune system respond differently to increases in iron concentration in vitro and in vivo. 2. Macrophages and lymphocytes differ in the H and L subunit content of the ferritins synthesized in response to increases in iron concentration in vitro. 3. NK activity by adherent and nonadherent cells differ in their susceptibility to the enhancing effect of lactoferrin in vitro. 4. Responses to mitogen stimulation by PHA and Con A are diminished, while the PWM response remains unaffected by exposure to acidic ferritins or by increasing concentrations of iron in vitro and in vivo. 5. Pretreatment of effector but not target cells with iron results in diminished responses in the MLR, an effect that appears to be related to the HLA-A locus. 6. In situ hybridization studies indicate that transferrin is synthesized by a specific subset of the T lymphocytes. 7. Transient increases in serum iron concentration above the full saturation of transferrin, reproducing the clinical situation frequently seen in hereditary hemochromatosis, are followed by a series of cellular changes in the synovium that can be correlated to changes in the course of an experimental model of arthritis in the rat.

Nodular sclerosing Hodgkin's disease in association with Gaucher's disease

Gaucher's disease has been described in association with a number of disorders of the lymphoreticular system. The patient described in this report developed Hodgkin's disease after treatment in childhood for Gaucher's disease. A possible pathogenetic link between the two disorders is discussed, together with the role of ferritinaemia.

Ferritin-bearing T-lymphocytes and serum ferritin in patients with breast cancer

Flow cytometric studies of T-lymphocytes in breast cancer patients show that the number of cells bearing ferritin on their surface is significantly greater than normal. The number of ferritin-bearing T-cells does not appear to be related to the clinical stage of the disease nor to the serum ferritin concentration, though this is higher in cancer patients than in normal women. There is no difference in the number of T-cells positive for interleukin 2 or transferrin receptors nor in the absolute number of T-cells, T-helper cells and B-cells between normal women and those with breast cancer or benign breast disease. However, there is a significant increase in the level of HLA DR-positive T-cells and T-suppressor cells in breast cancer patients. While the significance of ferritin-bearing T-cells is not known an increase in their number appears to be associated with cancer.

Ferritins in malignant and non-malignant lymphoid cells

Lymphoid cells from peripheral blood, thymus, malignant and non-malignant lymph nodes were analysed for ferritin content using radioimmunoassays specific for the 'acidic' H-subunit-rich and for 'basic' L-subunit-rich isoferritins, and the data were compared with the immunological characteristics of the cells. All tissues with high proportion of T or 'null' cells contained the lowest concentration of L-subunit-rich isoferritins, while the H-subunit-rich forms increased from low levels in the quiescent peripheral blood lymphocytes (PBL), to higher values in the immature and proliferating thymocytes and lymphoblasts, malignant or not. B-cell lymphomas contained concentrations of both ferritin types higher than those found in PBL. No significant difference was found in the isoferritin concentrations between non-malignant lymph nodes and tissues involved in Hodgkin's disease. These findings indicate that maturation stage, proliferative status and anatomical localization affect isoferritin expression in lymphoid cells.

Ferritin in neuroblastoma. Impact of tumor load and blood transfusions

Serial serum ferritin (SF) levels were measured in 36 patients with neuroblastoma seen at Memorial Sloan-Kettering Cancer Center (MSKCC) between January 1981 and December 1982. The significance of the associations among SF, stage and extent of disease, number of blood transfusions, liver function, serum iron (Fe), total iron-binding capacity (TIBC), and transferrin saturation was investigated. Although a dominant statistical correlation was found between SF and number of blood transfusions, the results suggest that amount of disease contributes to increasing SF levels. Serum ferritin levels increased on average in a linear fashion with number of blood transfusions in patients free of disease or with minimal disease. In patients with bulky disease, this increase was exponential (p value less than 0.01). Application of a reverse hemolytic plaque assay to the analysis of ferritin secretion by cells demonstrates that tumor cells do secrete ferritin in vitro.

The effect of desferrioxamine on the proliferative response of rat lymphocytes stimulated with various mitogens in vitro

This paper reports experiments designed to evaluate the effect of desferrioxamine on lymphocytes obtained from the spleen of Sprague-Dawley rats. The results showed that desferrioxamine inhibits the proliferative response of lymphocytes stimulated by concanavalin A or pokeweed mitogen, the effect being proportional to the dose used, and being maximal at the end of the culture period. To exert its effect, desferrioxamine has to be present from the initiation of the cultures--its addition 24 h later markedly reduced its inhibitory effect. Studies of cell viability indicated that the inhibition was not due to toxicity. Lymphocytes obtained from young animals (4 to 12-week-old) were more sensitive to desferrioxamine than older animals (13 to 18-week-old). Saturation of desferrioxamine with iron abolished its effect, suggesting a direct relationship between chelating properties and inhibition, and reinforcing the hypothesis that iron plays an important role in the process of cell division.

Hodgkin's disease: five steps from autoimmunity to cancer

A five-step hypothesis on the pathogenesis of Hodgkin's disease (HD) is presented. Weak immune suppressor activity gives a predisposition for the development of the disease, after which a non-specific immune stimulation can initiate a self-perpetuating uncontrolled stimulation between interdigitating cells (IDCs), macrophages and helper T lymphocytes (TH). The disease spreads to other lymph nodes through the secretion of humoral factors and by migration of cells. The response of the suppressor branch of the immune system is delayed, and comes from areas not yet involved in the disease, primarily from the spleen and bone marrow. Treatment will result in the predominance of the suppressor activity and allow calming of the disease. In a terminal phase, a possible neoplastic transformation of the chronically stimulated immune cells may give rise to frequent extranodal localizations and a rapid progression of the disease.

Isolation and characterization of a cDNA clone for human ferritin heavy chain

Ferritin, the main iron-storage protein, is composed of two partially homologous subunits, heavy (H) and light (L), with MrS of 21,000 and 19,000, respectively. We have isolated a cDNA clone for human ferritin H chains by screening a human lymphocyte cDNA library with synthetic oligodeoxyribonucleotides. The oligonucleotide sequences were derived from two pentapeptides found in human spleen ferritin. The selected clone hybridized to both probes and selected H-chain mRNA, but not L-chain mRNA, when hybridized to HeLa cell mRNA. These results indicate that the cloned DNA codes for a H chain of human ferritin. Since the amino acid sequence derived from the cloned DNA was almost identical to the partial amino acid sequence of a minor component found in human spleen ferritin, we conclude that the minor sequence found in human spleen ferritin must be a H subunit. Genomic analysis gives a complex pattern that suggests that ferritin H chains are encoded by a multigene family or have an unusually large number of exons.

Ferritin in normal human peripheral blood T-lymphocyte subpopulations

Six peripheral blood lymphoid fractions (total lymphocytes, non-T, T, Tar (autologous rosette-forming T cells/precursor), T mu (helper), and T gamma (suppressor) lymphocytes) isolated through rosetting procedures were examined for the presence of ferritin by a direct immunofluorescence technique. Although ferritin was present in all lymphoid fractions studied, a significantly higher proportion of ferritin-containing cells were detected in the T-cell fraction than in the non-T-cell fraction, (mean +/- SD = 7.9 +/- 1.6% and 5.0 +/- 1.2%, respectively). T mu- and T gamma-cell fractions showed a twofold increase in the number of ferritin-positive cells (14.1 +/- 1.4% and 15.4 +/- 2.6%, respectively), as compared with Tar (7.0 +/- 0.9%)-and total lymphocyte (6.9 +/- 1.3%)-cell fractions. These results indicate that ferritin is preferentially distributed in T mu and T gamma lymphocytes and may constitute the basis for explaining some of the roles exercised by these cells in the control of other biological systems.

Ferritin-bearing lymphocytes in patients with cancer

Ferritins, a group of isomeric proteins that have important functions in iron metabolism and storage, have been demonstrated to be carcinoembryonic antigens. It has been recently shown that a subpopulation of lymphocytes from the peripheral blood of patients with Hodgkin's disease or breast cancer bear ferritin on their surface membranes. In view of the potential diagnostic and prognostic value of ascertaining the number of ferritin-bearing lymphocytes, the authors developed a simple indirect immunofluorescent technique for identifying them and used this technique to examine the peripheral blood lymphocytes of 44 patients with carcinomas of the head and neck (26), colon (14), and lung (4). It was found that patients with cancer had a mean percentage of 10% ferritin-bearing lymphocytes in their peripheral blood as compared with 3.1% in controls. Ferritin binding did not appear to be influenced by a cell's capacity to form sheep erythrocyte (E) rosettes since no correlation could be found between the percentages of lymphocytes bearing ferritin and those forming three different varieties of E-rosettes. There appeared to be no correlation of the percentages of ferritin-bearing lymphocytes with clinical staging except for a small, but significant (P less than 0.05), increase in the number of patients with head and neck cancer and nodal metastases. Although the functional significance of ferritin-bearing lymphocytes is currently unknown, the appearance of this subpopulation of cells in the blood appears to be associated with cancer. This assay may prove to be useful as a diagnostic tool, as a prognostic tool, or as a means of identifying patients at a risk for developing cancer and, therefore, it deserves further exploration.

Distribution of ferritin, transferrin and lactoferrin in breast carcinoma tissue

An immunoperoxidase staining technique was used for detecting three major iron binding proteins (ferritin, transferrin and lactoferrin) in 40 breast carcinoma cases and six benign breast proliferative lesions. Ferritin staining was detected mainly in connectival stroma and in histiocytes surrounding neoplastic cells. Few and faint ferritin positivities were also detected in neoplastic cells of 20 carcinoma cases. Transferrin was found inconsistently in myoepithelial cells surrounding normal ductules, or around neoplastic ducts of ductal in situ carcinoma. In eight carcinoma cases, transferrin staining was also positive in neoplastic cells. Lactoferrin was detected only in normal breast epithelial cells and in benign breast proliferative lesions. These immunohistochemical findings may suggest that raised serum ferritin concentrations in breast carcinoma patients might be attributed to stromal reaction rather than to tumour synthesis. Transferrin staining of neoplastic cells in these carcinoma cases appears to be very intriguing, particularly since transferrin is considered an obligate requirement for growing cells, and transferrin receptors have been demonstrated only in dividing cells. On the basis of the immunohistochemical data, lactoferrin might be used as a pointer to benign lesions.