Iron, iron-binding proteins and immune system cells

The role of iron homeostasis in remodeling immune function and regulating inflammatory disease

The essential trace element iron regulates a wide range of biological processes in virtually all living organisms. Because both iron deficiency and iron overload can lead to various pathological conditions, iron homeostasis is tightly regulated, and understanding this complex process will help pave the way to developing new therapeutic strategies for inflammatory disease. In recent years, significant progress has been made with respect to elucidating the roles of iron and iron-related genes in the development and maintenance of the immune system. Here, we review the timing and mechanisms by which systemic and cellular iron metabolism are regulated during the inflammatory response and during infectious disease, processes in which both the host and the pathogen compete for iron. We also discuss the evidence and implications that immune cells such as macrophages, T cells, and B cells require sufficient amounts of iron for their proliferation and for mediating their effector functions, in which iron serves as a co-factor in toll-like receptor 4 (TLR4) signaling, mitochondrial respiration, posttranslational regulation, and epigenetic modification. In addition, we discuss the therapeutic implications of targeting ferroptosis, iron homeostasis and/or iron metabolism with respect to conferring protection against pathogen infection, controlling inflammation, and improving the efficacy of immunotherapy.

Chronic exposure to glyphosate induces transcriptional changes in honey bee larva: A toxicogenomic study

The honey bee Apis mellifera is the most abundant managed pollinator in diverse crops worldwide. Consequently, it is exposed to a plethora of environmental stressors, among which are the agrochemicals. In agroecosystems, the herbicide glyphosate (GLY) is one of the most applied. In laboratory assessments, GLY affects the honey bee larval development by delaying its moulting, among other negative effects. However, it is still unknown how GLY affects larval physiology when there are no observable signs of toxicity. We carried out a longitudinal experimental design using the in vitro rearing procedure. Larvae were fed with food containing or not a sub-lethal dose of GLY in chronic exposure (120 h). Individuals without observable signs of toxicity were sampled and their gene expression profile was analyzed with a transcriptomic approach to compare between treatments. Even though 29% of larvae were asymptomatic in the exposed group, they showed transcriptional changes in several genes after the GLY chronic intake. A total of 19 transcripts were found to be differentially expressed in the RNA-Seq experiment, mainly linked with defensive response and intermediary metabolism processes. Furthermore, the enriched functional categories in the transcriptome of the exposed asymptomatic larvae were linked with enzymes with catalytic and redox activity. Our results suggest an enhanced catabolism and oxidative metabolism in honey bee larvae as a consequence of the sub-lethal exposure to GLY, even in the absence of observable symptoms.

Genetic parameters for haemoglobin levels in sows and piglets as well as sow reproductive performance and piglet survival

Genetic parameters were estimated for haemoglobin (Hb) levels in sows and piglets as well as sow reproductive performance and piglet survival. Reproductive traits were available between 2005 and 2014 for 7857 litters from 1029 Large White and 858 Landrace sows. In 2012 and 2013, Hb levels, sow BW and sow back fat depth were measured on 348 sows with 529 litters 5 days prior to farrowing. In addition, Hb levels were available for 1127 one-day-old piglets from 383 litters (a maximum of three piglets per litter) of 277 sows with Hb levels. The average Hb levels in sows (sow Hb), their litters (litter Hb, based on average Hb of three piglets) and individual piglets (piglet Hb) were 112 ± 12.6 g/l, 103 ± 15.3 g/l and 105 ± 21.7 g/l, respectively. Heritabilities for Hb levels were 0.09 ± 0.07 for sow Hb, 0.19 ± 0.11 for litter Hb and 0.08 ± 0.05 for piglet Hb. Estimates for the permanent environment effect of sows were 0.09 ± 0.09 for sow Hb, 0.11 ± 0.12 for litter Hb and 0.12 ± 0.03 for piglet Hb. In comparison, heritabilities for both number of stillborn piglets and pre-weaning survival were lower (0.05 ± 0.01 and 0.04 ± 0.01). Sow BW had no significant heritability, while sow back fat depth was lowly heritable (0.10 ± 0.08). Positive genetic correlations were found between sow Hb and litter Hb (0.64 ± 0.47) and between litter Hb and sow back fat depth (0.71 ± 0.53). Higher litter Hb was genetically associated with lower number of stillborn piglets (-0.78 ± 0.35) and higher pre-weaning survival (0.28 ± 0.33). Negative genetic correlations between sow Hb and average piglet birth weight of the litter (-0.60 ± 0.34) and between piglet Hb and birth weight of individual piglets (-0.37 ± 0.32) indicate that selection for heavier piglets may reduce Hb levels in sows and piglets. Similarly, selection for larger litter size will reduce average piglet birth weight (rg: -0.40 ± 0.12) and pre-weaning survival (-0.57 ± 0.13) and may lead to lower litter Hb (-0.48 ± 0.27). This study shows promising first results for the use of Hb levels as a selection criterion in pig breeding programs, and selection for higher Hb levels may improve piglet survival and limit further reduction in Hb levels in sows and piglets due to selection for larger and heavier litters.

Overcoming the Histocompatibility Barrier: Transferrins as Carriers and Modulators of Immunogenic Identity

Proteic molecules were found in the bone marrow that were later identified as transferrins. When applied to transplantation of genetically incompatible bone marrow in supralethally irradiated recipient mice, the transferrins obtained from plasma of bone marrow donors promoted engraftment, permanent hemopoietic chimerism, and donor-type immune character. A combination of donor-matched transferrins and antigens was needed for induction of xenogeneic (interspecies) “tolerance” or unresponsiveness to donor antigens in chemically immunosuppressed mice treated with human transferrins and donor leucocytes. This novel and unique property of transferrins may explain the genesis and maintenance of immunogenic identity and allow a reshaping of the immune system. © 1998 Elsevier Science Inc.

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.

The theft of host heme by Gram-positive pathogenic bacteria

The element iron is essential for bacteria and plays a key role in the virulence and pathology of bacterial diseases. The largest reservoir of iron within the human body is in protoporphyrin IX, the compound commonly referred to as heme and bound by hemoglobin. For many years, the study of heme uptake in bacteria was restricted to Gram-negative organisms. However, recent studies have shed light on how bacteria containing a thick peptidoglycan, such as Gram-positive bacteria, acquire and transport heme. This review summarizes old and new research covering the acquisition, transport, and utilization of heme in Gram-positive bacterial pathogens.

Iron metabolism: microbes, mouse, and man

Recent advances in research on iron metabolism have revealed the identity of a number of genes, signal transduction pathways, and proteins involved in iron regulation in mammals. The emerging paradigm is a coordination of homeostasis within a network of classical iron metabolic pathways and other cellular processes such as cell differentiation, growth, inflammation, immunity, and a host of physiologic and pathologic conditions. Iron, immunity, and infection are intricately linked and their regulation is fundamental to the survival of mammals. The mutual dependence on iron by the host and invading pathogenic organisms elicits competition for the element during infection. While the host maintains mechanisms to utilize iron for its own metabolism exclusively, pathogenic organisms are armed with a myriad of strategies to circumvent these measures. This review explores iron metabolism in mammalian host, defense mechanisms against pathogenic microbes and the competitive devices of microbes for access to iron.

DNA, oligosaccharides, and mononucleotides stimulate oligomerization of human lactoferrin

Using small-angle X-ray scattering (SAXS), light scattering (LS), and soft laser ablation we have shown that lactoferrin (LF) in solution at neutral pH is oligomerized in the absence of salt or at physiological salt concentrations. The level of oligomerization depends on the concentration of LF, KCl or NaCl, and on the duration of the protein storage in solution. At the concentrations comparable with those in human milk (1-6 mg/ml), the average radius of gyration (R(g)) values of LF can attain 400-480 A, while fresh solution of previously lyophylized LF demonstrate a lower average R(g) (50-100 A), and R(g) value characterizing the LF monomer formed at 1 M NaCl is 26.7 A. The addition of oligonucleotides, oligosaccharides, or mononucleotides to LF in the presence or in the absence of KCl with different level of initial oligomerization accelerates the oligomerization rate and increases the R(g) values up to approximately 600-700 A, which correspond to associates containing ten or more protein molecules. During gel filtration on Sepharose 4B, high-degree LF oligomers dissociate nearly completely forming different degraded complexes, but in some cases it is possible to reveal small amount of a decamer. A possible role for oligomerization of LF, a highly polyfunctional protein, for its different biological activities is discussed.

Oral bovine lactoferrin improves bone status of ovariectomized mice

The aim of the present study was to evaluate the effect of dietary lactoferrin on bone metabolism in vivo using a postmenopausal animal model. We investigated whether bovine lactoferrin (bLF) ingestion could prevent bone loss in ovariectomized mice. Twelve-week-old female C3H mice either ovariectomized or sham operated were fed for 27 wk with the control diet (AIN-93M with 140 g of total milk protein as a protein source per kg of diet). Four groups of ovariectomized mice received diets including different concentrations of bLF (1, 5, 10, or 20 g of total milk protein were replaced by bLF). Ovariectomy induced a decreased uterine weight and a smaller gain of bone mineral density. Immunoreactive bLF was detected in the peripheral blood, and its concentration was related to the amount of bLF ingestion. bLF supplementation to the diet improved bone mineral density (BMD) and femoral failure load in a dose-dependent manner. We confirmed the direct effects of bLF in vitro using established and primary cultures of murine bone cells. Addition of bLF to the culture medium at a concentration of between 1 and 1,000 microg/ml stimulated both cell growth and differentiation of osteoblastic MC3T3 cells while inhibiting the growth of preosteoclastic RAW 267.4 cells. In primary culture of mixed bone cells, an enhanced osteoblast differentiation was associated with an inhibition of osteoclast differentiation at lower bLF concentrations (1-10 microg/ml). In conclusion, these findings suggest that dietary lactoferrin supplementation can have a beneficial effect on postmenopausal bone loss by modulating bone formation and resorption.

Induction of iron homeostasis genes during estrogen-induced uterine growth and differentiation

We have previously used genome-wide transcript profiling to investigate the relationships between changes in gene expression and physiological alterations during the response of the immature mouse uterus to estrogens. Here we describe the identification of a functionally inter-related group of estrogen-responsive genes associated with iron homeostasis, including the iron-binding protein lactotransferrin, the ferroxidase ceruloplasmin, the iron delivery protein lipocalin 2 and the iron-exporter ferroportin. Quantitative real-time PCR revealed that the expression of these genes increases with time during the uterotrophic response, reaching maximal levels in the post-proliferative phase (between 48 and 72 h). In contrast, the heme biosynthesis genes aminolevulinic acid synthase 1 and 2 were maximally induced by estrogen at 2 and 4 h, respectively, prior to increased cell proliferation. Together, these data reveal that estrogen induces the temporally coordinated expression of iron homeostasis genes in the mouse uterus, and suggest an important role for iron metabolism during sex steroid hormone-induced uterine cell growth and differentiation.

Iron inactivates the RNA polymerase NS5B and suppresses subgenomic replication of hepatitis C Virus

Clinical data suggest that iron is a negative factor in chronic hepatitis C; however, the molecular mechanisms by which iron modulates the infectious cycle of hepatitis C virus (HCV) remain elusive. To explore this, we utilized cells expressing a HCV replicon as a well-established model for viral replication. We demonstrate that iron administration dramatically inhibits the expression of viral proteins and RNA, without significantly affecting its translation or stability. Experiments with purified recombinant HCV RNA polymerase (NS5B) revealed that iron binds specifically and with high affinity (apparent Kd: 6 and 60 microM for Fe2+ and Fe3+, respectively) to the protein's Mg2+-binding pocket, thereby inhibiting its enzymatic activity. We propose that iron impairs HCV replication by inactivating NS5B and that its negative effects in chronic hepatitis C may be primarily due to attenuation of antiviral immune responses. Our data provide a direct molecular link between iron and HCV replication.

Balancing acts: molecular control of mammalian iron metabolism

Iron is ubiquitous in the environment and in biology. The study of iron biology focuses on physiology and homeostasis-understanding how cells and organisms regulate their iron content, how diverse tissues orchestrate iron allocation, and how dysregulated iron homeostasis leads to common hematological, metabolic, and neurodegenerative diseases. This has provided novel insights into gene regulation and unveiled remarkable links to the immune system.

Multiple enzymic activities of human milk lactoferrin

Lactoferrin (LF) is a Fe3+-binding glycoprotein, first recognized in milk and then in other human epithelial secretions and barrier fluids. Many different functions have been attributed to LF, including protection from iron-induced lipid peroxidation, immunomodulation and cell growth regulation, DNA binding, and transcriptional activation. Its physiological role is still unclear, but it has been suggested to be responsible for primary defense against microbial and viral infection. We present evidence that different subfractions of purified human milk LF possess five different enzyme activities: DNase, RNase, ATPase, phosphatase, and malto-oligosaccharide hydrolysis. LF is the predominant source of these activities in human milk. Some of its catalytically active subfractions are cytotoxic and induce apoptosis. The discovery that LF possesses these activities may help to elucidate its many physiological functions, including its protective role against microbial and viral infection.

The impact of previous HBV infection on the course of chronic hepatitis C

OBJECTIVE

Individuals with chronic hepatitis C who are anti-HBc positive may carry an occult hepatitis B virus (HBV) infection that can affect their response to antiviral therapy.

METHODS

In this study the prevalence of anti-HBc and HBV-DNA positivity was assessed in the serum and liver of 285 HCV-RNA-positive subjects treated with interferon-alpha at 5 mU/day for 12 months. The response to interferon (normal ALT and undetectable serum HCV-RNA) was evaluated at three different endpoints: 1) after 6 months; 2) at the end of treatment; and 3) 6 months after interferon discontinuation.

RESULTS

Ninety individuals were anti-HBc positive (32%), 2 of these were HBV-DNA positive in serum and 7 in liver (8%). None of the anti-HBc-negative individuals was HBV-DNA positive in serum or liver. The prevalence of cirrhosis was greater in the anti-HBc-positive group than in the anti-HBc-negative group (p < 0.05), whereas HCV-RNA levels were lower. Anti-HBc-positive individuals had a lower response rate to interferon at 6 months and at the end of treatment as compared to anti-HBc-negative subjects (respectively 42% vs 66%, p < 0.01; and 32% vs 57%, p < 0.01). No difference between the two groups in terms of sustained response was detected 6 months after interferon discontinuation.

CONCLUSIONS

The prevalence of anti-HBc is high among HCV-positive individuals. HCV-positive individuals who are anti-HBc positive have: 1) a higher prevalence of cirrhosis; 2) lower HCV-RNA levels; and 3) an impaired ability to respond to interferon treatment.

Haemochromatosis

Arthropathy is a prominent but still underappreciated aspect of haemochromatosis. Clinical descriptions have characterized typical features, including involvement of the 2nd-3rd metacarpophalangeal joints with an osteoarthritic-like picture. Virtually any joint can be involved and can be a presenting clue to the underlying disease. The recent demonstration of the HFE gene on chromosome 6 with characteristic mutations should encourage further investigation. However, the pathogenesis of the arthropathy is not yet well understood. Treatment is also empirical and often unsatisfactory. Phlebotomies, although valuable to treat or prevent other features, do not predictably benefit the arthropathy.

Characterization of Korean native goat lactoferrin

We purified lactoferrin from the colostrum of the Korean native goat (Capra hircus) by ion-exchange chromatography using CM-Toyopearl 650M followed by affinity chromatography on AF-Heparin Toyopearl 650M. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis suggested the molecular mass of Korean native goat lactoferrin is 82 kDa with an iron saturation of 30% as estimated by spectroscopic analysis. Circular dichroism analysis shows goat lactoferrin molecule contains 24.5%, alpha-helix; 36.0%, beta-structure; 13.5%, beta-turn and 26.0%, unordered structure. Heparin binding affinity is the same as that of bovine lactoferrin, but lower than that of human lactoferrin. An analysis using synthetic peptides shows that the peptide from residue 22 to 31--WQRRMRKLGA--exerts a positive heparin-binding ability.

Human milk lactoferrin binds two DNA molecules with different affinities

Evidence is presented that lactoferrin (LF), an Fe3+-binding glycoprotein, possesses two DNA-binding sites with different affinities for specific oligonucleotides (ODNs) (Kdl = 8 nM; Kd2 approximately 0.1 mM). The high affinity site became labeled after incubation with affinity probes for DNA-binding sites; like the antibacterial and polyanion-binding sites, this site was shown to be located in the N-terminal domain of LF. Interaction of heparin with the polyanion-binding site inhibits the binding of ODNs to both sites. These data suggest that the DNA-binding sites of LF coincide or overlap with the known polyanion and antimicrobial domains of the protein.

Iron compounds after erythrophagocytosis: chemical characterization and immunomodulatory effects

In humans, the lymphomyeloid system has a fundamental role on iron metabolism promoting its recycling due to a continuous removal of effete red blood cells. Additionally, one of the most intriguing aspects of metalloporphyrins in biology is their effect on the immune system. However, the process of erythrocyte catabolism is still poorly understood and needs further research. In the present study, we attempt to investigate the nature and the possible physiologic role of Fe compounds released after erythrophagocytosis during the removal of red blood cells. Monocyte erythrophagocytosis in vitro experiments were done to characterize chemically the Fe compounds present inside the cells and in the culture supernatants. We tested the probable immunomodulatory functions of erythrophagocytosis products over lymphocyte cultures activated in vitro with T mitogens (alpha-CD3). Data obtained from atomic absorption spectroscopy confirmed the presence of Fe in the culture supernatants of monocyte cultures after erythrophagocytosis. Also, high-spin haem complexes derived from erythrocyte catabolism were detected by electron paramagnetic electronic resonance. Finally, in vitro activated lymphocyte proliferation experiments indicate the co-mitogenic properties of monocyte culture supernatants after red blood cells phagocytosis. Thus, the results of the present work provide evidence that culture monocyte supernatants after in vitro erythrophagocytosis contain Fe (III) high-spin haem complexes and show lymphocyte proliferation co-stimulatory properties.

Identification of an alternative form of human lactoferrin mRNA that is expressed differentially in normal tissues and tumor-derived cell lines

Lactoferrin (LF), traditionally known as an iron-binding protein present in high concentrations in milk and various secretions, has emerged as a multifunctional protein involved in many aspects of the host defense against infection. Recently, LF has been shown to inhibit the growth of solid tumors and reduce experimental metastasis in mice, suggesting that LF also may play a role in the defense against tumorigenesis. Here we provide the sequence of the cDNA and promoter region, the chromosome assignment, and tissue expression pattern of a novel form of LF mRNA (delta LF). The sequence of delta LF mRNA is nearly identical to that of LF mRNA; however, at the 5' end, we find a novel sequence that replaces the N-terminal signal peptide sequence of LF mRNA. We map the delta LF mRNA to human chromosome 3 and find that both delta LF and LF sequences colocalize to the same cloned 90- to 150-kb genomic DNA fragment. We further show that the delta LF mRNA is the product of alternative splicing of the LF gene and likely is specified by use of an alternative promoter. Although we find delta LF mRNA at various levels in 20 of 20 adult and fetal human tissues, we do not find delta LF mRNA in any of 14 diverse tumor-derived cell lines.

Bovine lactoferrin and lactoferricin, a peptide derived from bovine lactoferrin, inhibit tumor metastasis in mice

We investigated the effect of a bovine milk protein, lactoferrin (LF-B), and a pepsin-generated peptide of LF-B, lactoferricin (Lfcin-B), on inhibition of tumor metastasis produced by highly metastatic murine tumor cells, B16-BL6 melanoma and L5178Y-ML25 lymphoma cells, using experimental and spontaneous metastasis models in syngeneic mice. The subcutaneous (s.c.) administration of bovine apo-lactoferrin (apo-LF-B, 1 mg/mouse) and Lfcin-B (0.5 mg/mouse) 1 day after tumor inoculation significantly inhibited liver and lung metastasis of L5178Y-ML25 cells. However, human apolactoferrin (apo-LF-H) and bovine holo-lactoferrin (holo-LF-B) at the dose of 1 mg/mouse failed to inhibit tumor metastasis of L5178Y-ML25 cells. Similarly, the s.c. administration of apo-LF-B as well as Lfcin-B, but not apo-LF-H and holo-LF-B, 1 day after tumor inoculation resulted in significant inhibition of lung metastasis of B16-BL6 cells in an experimental metastasis model. Furthermore, in in vivo analysis for tumor-induced angiogenesis, both apo-LF-B and Lfcin-B inhibited the number of tumor-induced blood vessels and suppressed tumor growth on day 8 after tumor inoculation. However, in a long-term analysis of tumor growth for up to 21 days after tumor inoculation, single administration of apo-LF-B significantly suppressed the growth of B16-BL6 cells throughout the examination period, whereas Lfcin-B showed inhibitory activity only during the early period (8 days). In spontaneous metastasis of B16-BL6 melanoma cells, multiple administration of both apo-LF-B and Lfcin-B into tumor-bearing mice significantly inhibited lung metastasis produced by B16-BL6 cells, though only apo-LF-B exhibited an inhibitory effect on tumor growth at the time of primary tumor amputation (on day 21) after tumor inoculation. These results suggest that apo-LF-B and Lfcin-B inhibit tumor metastasis through different mechanisms, and that the inhibitory activity of LF-B on tumor metastasis may be related to iron (Fe3+)-saturation.

Elevated serum iron predicts poor response to interferon treatment in patients with chronic HCV infection

To date, there are no firm clinical, demographic, biochemical, serologic, or histologic features predicting which patients with chronic hepatitis C are more likely to respond to therapy with interferon-alpha. Serum iron, total iron-binding capacity, transferrin saturation, and ferritin were measured in the fasting state. The amount of stainable iron in liver biopsy specimens was evaluated histochemically as well. All patients received subcutaneous recombinant human IFN-alpha 2a three million units thrice weekly by self-administration. Eleven of 13 (84%) responders had low to normal serum iron levels as compared to one of 26 (4%) nonresponders (P < 0.001). The serum transferrin was similar in both groups, but iron saturation was significantly lower in responders (30 +/- 10%) than in nonresponders (53 +/- 12%) (P< 0.001). Serum ferritin and hepatic iron content were higher in nonresponders (NS). It is suggested that increased serum iron and transferrin saturation blunt the action of interferon, as they have opposite effects on the immune system. Iron overload can thus lead to a poor response to interferon. It remains to be seen whether reducing iron overload will improve the response to interferon therapy.

Yersinia infections in patients with homozygous beta-thalassemia associated with iron overload and its treatment

Patients with homozygous beta-thalassemia are at increased risk of serious infections. Yersinia enterocolitica is an organism with a predilection for these and other iron-overloaded patients. Three young adult patients with beta-thalassemia who were chronically transfused and developed yersiniosis are reported. Iron overload and desferrioxamine use are predisposing factors, as supported by clinical, animal, and in vitro data. Iron excess both immunologically compromises the host and greatly enhances yersinial growth. Desferrioxamine may make host iron even more bioavailable to Yersinia. Recognition of this association and unusual manifestations in these patients such as an appendicitis-like syndrome may direct clinicians to earlier antiyersinial therapy and temporary cessation of chelation.

Iron carrier proteins facilitate engraftment of allogeneic bone marrow and enduring hemopoietic chimerism in the lethally irradiated host

Cell-free supernatants of rabbit bone marrow were fractionated, separated, and purified by Ultrogel and Superose chromatography. A single fraction promoted engraftment of allogeneic bone marrow and enduring hemopoietic chimerism across the H-2 barrier in lethally irradiated mice. This "bio-active" fraction, analyzed by reducing SDS-PAGE electrophoresis, and transblotted on PVDF membrane, and purified by reverse-phase HPLC and SDS-PAGE electrophoresis yielded a main prealbumin band that when examined for primary structure by Edman degradation, proved to be rabbit transferrin. This was also attested by highly specific precipitation of the prealbumin band with polyclonal antibodies to rabbit transferrin. Iron-saturated human transferrin, lactotransferrin, and egg transferrin (conalbumin) were assayed in irradiated C57BL/6 mice infused with bone marrow from histoincompatible BALB/c donors. Mice treated with iron-loaded transferrins survive and develop enduring allogeneic chimerism with no discernible signs of graft-versus-host disease. Iron carrier proteins thus provide an unique means of achieving successful engraftment of allogeneic bone marrow in immunologically hostile murine H-2 combinations.

Iron and immunity

Review of animal and human studies concerning the impact of iron deficiency on immune function in vivo indicates that in many instances there is no firm consensus of opinion as to the relationship between iron status and immunity. One major problem with almost all human studies is that other micro- and macronutrient deficiencies are inadequately controlled for and thus it is often unclear as to whether reported abnormalities of immune function can be attributed specifically to iron deficiency. Even when abnormalities of immune function have been detected it is often uncertain as to the biological and clinical relevance that these may have for the host. Within these restraints the available studies suggest that iron deficiency may at least contribute to impaired T lymphocyte function as judged by DTH responses in skin and impaired mitogen-induced proliferation. As in protein energy malnutrition, humoral immunity is largely spared in humans, the balance of evidence suggesting that immunoglobulin production and function is normal, as are serum concentrations of complement. The only other abnormality of non-specific immunity which has been reported consistently to be abnormal is that of reduced bactericidal activity of polymorphonuclear leucocytes. The clinical relevance of these abnormalities remains to be established. There is, however, no evidence to suggest that individuals with iron deficiency suffer the devastating infective complications of the well defined immunodeficiency syndromes either congenital or acquired. It seems likely therefore that despite the fundamental importance of iron in maintaining the integrity of immune function, humans can tolerate the extremes of deficiency and excess and survive in a relatively healthy state.

Iron exerts a specific inhibitory effect on CD2 expression of human PBL

The effect of in vitro exposure to ferric citrate (Fe-citrate) on the expression of human lymphocyte surface markers was studied. The following markers were examined: E-rosette formation, CD2, CD3, CD4, CD8, CD1, CD22, CD10 and HLA-DR. Pretreatment of peripheral blood lymphocytes (PBL) with Fe-citrate at concentrations ranging from 10(-2) M to 10(-5) M resulted in the exclusive inhibition of E-rosette formation and CD2 expression. None of the other surface antigens examined appeared to be sensitive to the Fe-citrate treatment. Competition experiments further indicated that iron interacts specifically with CD2 on T lymphocytes.