An immunoradiometric assay for the acidic ferritin of human heart: application to human tissues, cells and serum

Serum or plasma ferritin concentration as an index of iron deficiency and overload

BACKGROUND

Reference standard indices of iron deficiency and iron overload are generally invasive, expensive, and can be unpleasant or occasionally risky. Ferritin is an iron storage protein and its concentration in the plasma or serum reflects iron stores; low ferritin indicates iron deficiency, while elevated ferritin reflects risk of iron overload. However, ferritin is also an acute-phase protein and its levels are elevated in inflammation and infection. The use of ferritin as a diagnostic test of iron deficiency and overload is a common clinical practice.

OBJECTIVES

To determine the diagnostic accuracy of ferritin concentrations (serum or plasma) for detecting iron deficiency and risk of iron overload in primary and secondary iron-loading syndromes.

SEARCH METHODS

We searched the following databases (10 June 2020): DARE (Cochrane Library) Issue 2 of 4 2015, HTA (Cochrane Library) Issue 4 of 4 2016, CENTRAL (Cochrane Library) Issue 6 of 12 2020, MEDLINE (OVID) 1946 to 9 June 2020, Embase (OVID) 1947 to week 23 2020, CINAHL (Ebsco) 1982 to June 2020, Web of Science (ISI) SCI, SSCI, CPCI-exp & CPCI-SSH to June 2020, POPLINE 16/8/18, Open Grey (10/6/20), TRoPHI (10/6/20), Bibliomap (10/6/20), IBECS (10/6/20), SCIELO (10/6/20), Global Index Medicus (10/6/20) AIM, IMSEAR, WPRIM, IMEMR, LILACS (10/6/20), PAHO (10/6/20), WHOLIS 10/6/20, IndMED (16/8/18) and Native Health Research Database (10/6/20). We also searched two trials registers and contacted relevant organisations for unpublished studies.

SELECTION CRITERIA

We included all study designs seeking to evaluate serum or plasma ferritin concentrations measured by any current or previously available quantitative assay as an index of iron status in individuals of any age, sex, clinical and physiological status from any country.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methods. We designed the data extraction form to record results for ferritin concentration as the index test, and bone marrow iron content for iron deficiency and liver iron content for iron overload as the reference standards. Two other authors further extracted and validated the number of true positive, true negative, false positive, false negative cases, and extracted or derived the sensitivity, specificity, positive and negative predictive values for each threshold presented for iron deficiency and iron overload in included studies. We assessed risk of bias and applicability using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS)-2 tool. We used GRADE assessment to enable the quality of evidence and hence strength of evidence for our conclusions.

MAIN RESULTS

Our search was conducted initially in 2014 and updated in 2017, 2018 and 2020 (10 June). We identified 21,217 records and screened 14,244 records after duplicates were removed. We assessed 316 records in full text. We excluded 190 studies (193 records) with reasons and included 108 studies (111 records) in the qualitative and quantitative analysis. There were 11 studies (12 records) that we screened from the last search update and appeared eligible for a future analysis. We decided to enter these as awaiting classification. We stratified the analysis first by participant clinical status: apparently healthy and non-healthy populations. We then stratified by age and pregnancy status as: infants and children, adolescents, pregnant women, and adults. Iron deficiency We included 72 studies (75 records) involving 6059 participants. Apparently healthy populations Five studies screened for iron deficiency in people without apparent illness. In the general adult population, three studies reported sensitivities of 63% to 100% at the optimum cutoff for ferritin, with corresponding specificities of 92% to 98%, but the ferritin cutoffs varied between studies. One study in healthy children reported a sensitivity of 74% and a specificity of 77%. One study in pregnant women reported a sensitivity of 88% and a specificity of 100%. Overall confidence in these estimates was very low because of potential bias, indirectness, and sparse and heterogenous evidence. No studies screened for iron overload in apparently healthy people. People presenting for medical care There were 63 studies among adults presenting for medical care (5042 participants). For a sample of 1000 subjects with a 35% prevalence of iron deficiency (of the included studies in this category) and supposing a 85% specificity, there would be 315 iron-deficient subjects correctly classified as having iron deficiency and 35 iron-deficient subjects incorrectly classified as not having iron deficiency, leading to a 90% sensitivity. Thresholds proposed by the authors of the included studies ranged between 12 to 200 µg/L. The estimated diagnostic odds ratio was 50. Among non-healthy adults using a fixed threshold of 30 μg/L (nine studies, 512 participants, low-certainty evidence), the pooled estimate for sensitivity was 79% with a 95% confidence interval of (58%, 91%) and specificity of 98%, with a 95% confidence interval of (91%, 100%). The estimated diagnostic odds ratio was 140, a relatively highly informative test. Iron overload We included 36 studies (36 records) involving 1927 participants. All studies concerned non-healthy populations. There were no studies targeting either infants, children, or pregnant women. Among all populations (one threshold for males and females; 36 studies, 1927 participants, very low-certainty evidence): for a sample of 1000 subjects with a 42% prevalence of iron overload (of the included studies in this category) and supposing a 65% specificity, there would be 332 iron-overloaded subjects correctly classified as having iron overload and 85 iron-overloaded subjects incorrectly classified as not having iron overload, leading to a 80% sensitivity. The estimated diagnostic odds ratio was 8.

AUTHORS' CONCLUSIONS

At a threshold of 30 micrograms/L, there is low-certainty evidence that blood ferritin concentration is reasonably sensitive and a very specific test for iron deficiency in people presenting for medical care. There is very low certainty that high concentrations of ferritin provide a sensitive test for iron overload in people where this condition is suspected. There is insufficient evidence to know whether ferritin concentration performs similarly when screening asymptomatic people for iron deficiency or overload.

Peptide-Mediated Immobilization on Magnetoferritin for Enzyme Recycling

Ferritin possess favorable properties because its exterior and interior surface can be applied to generate functional nanomaterials, which make them possible for enzyme immobilization and recycling. Here, we report the noncovalent immobilization of a genetically modified β-glucosidase onto the outer surface of synthetic magnetoferritin through the electrostatic interaction of a heterodimeric coiled-coil protein formed by coils containing lysine residues (K-coils) and coils containing glutamic acid (E-coils). The immobilized enzyme was characterized, and its enzymatic properties were evaluated. Furthermore, reusability of immobilized enzyme was demonstrated in aqueous solution under an applied magnetic field. The results showed that magnetoferritin was successfully prepared and it was an excellent support for enzyme immobilization. After three times usages, the retention rates were 93.75%, 82.5%, and 56.25%, respectively, demonstrating that immobilized enzyme possessed good retention efficiency and could be used as potential carrier for other biomolecules. The strategy of enzyme immobilization developed in this work can be applied, in general, to many other target molecules.

Performance and comparability of laboratory methods for measuring ferritin concentrations in human serum or plasma: A systematic review and meta-analysis

BACKGROUND

Different laboratory methods are used to quantify ferritin concentrations as a marker of iron status. A systematic review was undertaken to assess the accuracy and comparability of the most used methods for ferritin detection.

METHODS AND FINDINGS

National and regional databases were searched for prospective, retrospective, sectional, longitudinal and case-control studies containing the characteristics and performance of at least one method for serum/plasma ferritin determinations in humans published to date. The analysis included the comparison between at least 2 methods detailing: sensitivity, precision, accuracy, predictive values, inter-methods adjustment, and use of international reference materials. Pooled method performance was analyzed for each method and across methods.

OUTCOMES

Search strategy identified 11893 records. After de-duplication and screening 252 studies were assessed, including 187 studies in the qualitative analysis and 148 in the meta-analysis. The most used methods included radiometric, nonradiometric and agglutination assays. The overall within-run imprecision for the most reported ferritin methods was 6.2±3.4% (CI 5.69-6.70%; n = 171), between-run imprecision 8.9±8.7% (CI 7.44-10.35%; n = 136), and recovery rate 95.6% (CI 91.5-99.7%; n = 94). The pooled regression coefficient was 0.985 among all methods analyzed, and 0.984 when comparing nonradiometric and radiometric methods, without statistical differences in ferritin concentration ranging from 2.3 to 1454 μμg/L.

CONCLUSION

The laboratory methods most used to determine ferritin concentrations have comparable accuracy and performance. Registered in PROSPERO CRD42016036222.

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.

Relation between iron content of serum ferritin and clinical status factors extracted by factor analysis in patients with hyperferritinemia

OBJECTIVES

The aims of this study were to develop a new technique for determination of iron content of serum ferritin (ICF, micromol Fe/mg protein) and to investigate relations between ICF and clinical status in patients with hyperferritinemia.

METHODS

ICF values were determined by a combination of immunoprecipitation of ferritin and direct colorimetric iron assay. One hundred fifty patients with hyperferritinemia were screened. Factor analysis of the results of 11 laboratory tests was applied to extract factors representing the clinical status of patients. Relations between the extracted factors and the ICF values or serum ferritin concentrations were assessed.

RESULTS

Within-run coefficients of variation (CVs) of the ICF assay were <==5.7%. The mean ICF value of 150 patients was 0.423 micromol/mg (SD, 0.211 micromol/mg). Three factors representing clinical status were identified: inflammation, tissue cell damage, and body iron status. Serum ferritin level correlated with all three factors. In contrast, ICF correlated significantly only with the factor representing tissue cell damage (r = 0.293, p = 0.001), and this correlation was independent of inflammation and iron status (p = 0.008).

CONCLUSIONS

ICF changes in response to tissue cell damage independent of inflammatory and body iron statuses, whereas serum ferritin changes in response to all three pathologic statuses.

Camel kidney ferritin: isolation and partial characterization

Camel kidney ferritin was isolated from a tissue homogenate by thermal denaturation, ammonium sulphate fractionation, Sephacryl S-300 gel filtration and DEAE-blue gel affinity chromatography. The yield and the iron and neutral carbohydrate contents were 0.012 mg/g wet tissue, 4.0% and 2.7%, respectively. The phosphate:iron ratio was 0.13, twofold lower than that reported for camel liver ferritin. Native gel electrophoresis revealed the presence of a monomeric ferritin. SDS gel electrophoresis and immunoblotting showed two types of subunits, heavy and light, contrary to the extensive heterogeneity observed in camel liver ferritin. In general, the tissue ferritins shared a similar amino acid composition. However, a twofold lower glycine and an eightfold higher arginine content were recorded for camel kidney ferritin. In addition, kidney ferritin had a relatively high content of glutamic acid. Cross-reactivity studies by Ouchterlony double diffusion and noncompetitive indirect ELISA revealed a distinct cross-reactivity between buffalo ferritin antiserum and camel liver ferritin, but camel liver ferritin showed only weak cross-reactivity.

International collaborative study to evaluate a recombinant L ferritin preparation as an International Standard

A recombinant L ferritin preparation, lyophilized in ampoules and designated 94/572, was evaluated by 18 laboratories in 9 countries for its suitability as an International Standard (IS). The preparation was assayed in a wide range of in-house and commercial immunoassays against the 2nd IS for ferritin (of spleen origin; 80/578). The immunological reactivity of the recombinant material was similar to that of the 2nd IS for ferritin in the majority of assays and demonstrated adequate stability in accelerated degradation studies. On the basis of the results presented here, the WHO Expert Committee on Biological Standardization established 94/572 as the 3rd IS for ferritin, recombinant.

Postmortem blood ferritin concentrations in sudden infant death syndrome

AIMS--To confirm the observation of extremely high concentrations of ferritin in postmortem serum samples in sudden infant death syndrome (SIDS); to examine the factors influencing blood ferritin concentrations postmortem; to determine whether or not these high blood ferritin concentrations are characteristic of SIDS. METHODS--Postmortem samples of cardiac blood were obtained from 58 full term infants who died of SIDS and 14 full-term infants who died of a variety of other causes. Whole blood and serum ferritin concentrations were determined and compared with age at death, liver iron concentration, serum iron concentration, and serum lactate dehydrogenase activity. RESULTS--The median postmortem blood ferritin concentration for all infants was 18,600 micrograms/l, which is about 200 times the concentration found in the serum of normal, live infants. Serum iron concentrations were high and there was a highly significant correlation between serum ferritin and iron concentrations suggesting that much of the serum iron was contributed by ferritin. There was no significant difference between serum and whole blood ferritin concentrations. H to L type ferritin ratios were higher in blood from the left than the right ventricle of the heart but the ferritin was always predominantly L type. Blood ferritin concentrations rose rapidly after death but in samples collected at postmortem examination there was a significant correlation with liver iron concentration and an inverse correlation with age. Median values for blood ferritin were higher in SIDS (22,500; n = 58) than in control cases (6900; n = 7) dying under one year of age; however, in both groups ferritin concentrations decreased with age. CONCLUSIONS--Release of ferritin into the blood postmortem seems to be characteristic of infants dying before the age of one year rather than characteristic of SIDS. Two factors may cause such ferritin release postmortem: tissue breakdown and the high level of storage iron in cells of the reticuloendothelial system (including endothelial cells lining vessel walls). SIDS occurs when tissue iron concentrations are higher than at any other time of life. It is possible that the ready availability of iron enhances free radical damage which might be implicated in SIDS.

Red cell dimorphism in a young man with a constitutional chromosomal translocation t(11;22)(p15.5;q11.21)

A constitutional, balanced chromosomal translocation t(11;22)(p15.5;q11.21) was discovered in a tall young man during investigation of a red cell dimorphism. The red cells are predominantly normochromic and normocytic with a small population of hypochromic, microcytic cells. Contained within the regions involved in the translocation are determinants of height (IGF2:11p15.5), red cell haemoglobinization (non-alpha globin gene complex: 11p15.5) and oncogenesis (cHa-Ras-1, Beckwith-Wiedemann syndrome: 11p15.5; BCR, Burkitts lymphoma, Ewings sarcoma: 22q11.21). To map these regions in the patient, somatic cell hybrids were generated and cell lines that segregated the chromosomes 11, 22 and 22q- were obtained. All 11p15.5 sequences investigated, in particular the whole of the non-alpha globin gene complex including its 5' and 3' regulatory sequences, were found to be translocated to 22q-. All chromosome 22 sequences studied were missing from the 22q- cell lines, including the proximal anonymous marker D22S24, and therefore assumed to be translocated to 11p+. These results suggest that the non-alpha globin gene complex has been moved close to the centromeric region of chromosome 22q-. It is postulated that such a positioning subjects the complex to a variegated position-effect bringing about a clonal exclusion of the complex and thus producing a beta-thalassaemia trait mosaic.

Red cell destruction by human monocytes--changes in intracellular ferritin concentration and phenotype

Mononuclear cells from 5 normal men and 5 patients homozygous for hereditary haemochromatosis (HFE) have been incubated for 18 h with or without the addition of sheep red blood cells coated with antibody (SRBC). In the absence of SRBC mean H type ferritin concentrations were greater than L type (normals: mean L type 11.6 ng/10(6) cells, H type 15.5; patients, L type 23.5 ng/10(6) cells, H type 41.6). In the presence of SRBC, monocyte L type ferritin concentrations increased considerably (76 ng/10(6) cells in normals and 141 ng/10(6) cells in patients) but H type ferritin concentrations were the same or decreased compared with incubation in medium only. Incubation with additional iron (ferric ammonium citrate, 2.5 micrograms Fe/ml) increased both H and L type ferritin concentrations. Erythrophagocytosis thus appears to cause differential regulation of H and L ferritin subunit synthesis or breakdown. Normal subjects and patients do not differ in this response to erythrophagocytosis.

Immunological properties of ferritin during in vitro maturation of human monocytes

Ferritin in macrophages from human liver and spleen is rich in L subunits but, in the peripheral blood monocytes from which tissue macrophages are derived, the ferritin contains a high proportion of H subunits. We have studied the maturation of monocytes in vitro and the immunological properties of cellular ferritin during this process. Mononuclear cells were isolated from peripheral blood of normal subjects and patients with idiopathic haemochromatosis. Monocytes were obtained by incubation on plastic. The adherent cells were incubated in medium with or without added iron (ferric ammonium citrate) for 20 hours and harvested. Monocytes were also incubated for 7 days before incubation with iron. Ferritin concentrations were determined using immunoassays specific for H and L rich isoferritins. Freshly isolated monocytes were found to have similar concentrations of H- and L-rich isoferritins. Incubation with iron caused an increase in both H- and L-type ferritins. After incubation for 7 d the ferritin present in the normal cell lysates was L-rich and incubation with iron caused accumulation of L-, but not H-type ferritin. Maturation of monocytes is thus associated with the loss of H-rich isoferritins. There were no differences between normal subjects and patients with idiopathic haemochromatosis in ferritin concentrations. In vitro maturation provides an excellent model for studying the developmental control of ferritin synthesis and breakdown.

Expression of cell surface transferrin receptor and intracellular ferritin after in vitro stimulation of peripheral blood T lymphocytes

Measurements of peripheral blood lymphocyte surface transferrin receptor using flow cytometry show that phytohaemagglutinin (PHA) stimulation causes a marked increase in both the number of cells bearing receptors and the absolute number of receptors. This increase is accompanied by the interleukin-2 receptor and there is a progressive increase of cells in the S phase of their cycle. Furthermore, ferritin synthesis in proliferating cells, as determined by immunoprecipitation techniques, increases significantly compared to non-stimulated cells. Intracellular concentrations of both spleen-type and heart-type ferritin are also increased with a preferentially high proportion of heart-type ferritin. These results suggest that expression of transferrin receptor and synthesis of ferritin is regulated by a complex mechanism. Cellular proliferative activity increases the expression of transferrin receptor and could modulate the biosynthesis of intracellular ferritin that is normally controlled by iron. These two processes do not appear to be linked.

Luminol peroxidation catalyzed by human isoferritins

The role of ferritin in catalyzing the oxidation of luminol with the production of chemiluminescence was investigated. The effect of pH was compared to its effect on K3Fe(CN)6-catalyzed oxidation and different pH optima were recorded for the two catalysts. The ferrous iron chelator, bipyridyl, enhanced the production of chemiluminescence catalyzed by FeSO4 and ferritin but had little effect on the K3Fe(CN)6-catalyzed reaction. Desferal reduced the level of chemiluminescence in the presence of FeSO4 and ferritin but was a much more effective inhibitor of chemiluminescence catalyzed by K3Fe(CN)6. The hydroxyl radical scavenger, mannitol, had little effect upon light production whereas superoxide dismutase inhibited light production. The addition of antihuman spleen ferritin completely inhibited activity. The catalytic activity of both H and L rich ferritins was affected by iron content. Activity increased until the Fe/protein ratio reached 0.04 micrograms Fe/micrograms protein and then decreased with increasing iron content. Thus activity is controlled by the iron content of the molecule and influenced by its subunit composition as is the uptake of iron into ferritin. These findings suggest that ferroxidation by ferritin is associated with the ability to generate radicals of the nitrogenous base luminol with the production of chemiluminescence. Although activity is greatest at alkaline pH there is significant activity at pH 7.4. Ferritin therefore may be able to generate free radical reactions in vivo with the acidic isoferritin being most active.

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.

Duodenal iron proteins in idiopathic hemochromatosis

This study was undertaken to assess the relationship between iron absorption and the concentration of duodenal iron proteins in normal subjects and patients with idiopathic hemochromatosis (IH). Biopsies were obtained endoscopically from the duodenum in 17 normal subjects, 3 of whom were mildly iron deficient, and 7 patients with untreated IH. The absorption of both heme and nonheme iron was increased in IH despite a 20-fold elevation in serum ferritin. Immunoassays using MAb were used to measure transferrin, H-rich ferritin, and L-rich ferritin in mucosal samples. Mucosal transferrin concentrations in normal subjects did not correlate with either iron status or iron absorption, indicating that mucosal transferrin plays no physiological role in iron absorption. Mucosal transferrin was significantly lower in IH, presumably because of a decrease in mucosal transferrin receptors. Mucosal H and L ferritin concentrations were directly related to body iron stores and inversely related to iron absorption in normal subjects. In IH, mucosal H and L ferritin failed to increase in parallel with the serum ferritin, but were appropriate for the level of iron absorption. The relationship of mucosal H/L ferritin in IH did not differ from that observed in normal subjects. Our findings indicate that the major abnormality in duodenal iron proteins in IH is a parallel decrease in the concentration of H- and L-rich ferritin. It is not evident whether this is the result or the cause of the absorptive abnormality.

Basic and acidic isoferritins in the sera of patients with neuroblastoma

Serum ferritin frequently is elevated in patients with neuroblastoma. Isoferritins extracted from neuroblastoma tumors and cells in culture show a wide range from basic (rich in L subunit) to acidic (rich in H subunit) isoferritins. Total ferritin is a combination of basic and acidic isoferritins. Forty-four serum samples from 25 patients with neuroblastoma were measured for basic and acidic isoferritin levels by radioimmunoassay using antibodies to liver (basic) ferritin and HeLa (acidic) ferritin. Normal ranges for basic and acidic serum ferritins were 7 to 142 ng/ml (median, 30 ng/ml) and 0 to 12 ng/ml (median, 3.4), respectively. Basic ferritins in the 44 neuroblastoma sera ranged from 0 to 1460 ng/ml, and acidic ferritins, 0 to 40 ng/ml. Sera with high levels of acidic ferritins always had increased basic ferritins. Thus, acidic/basic ferritin ratios were nearly constant, less than 0.3 in all sera. There was a significant linear correlation between basic and acidic isoferritins (r = 0.833). These results suggest that neuroblastoma tumors produce both basic and acidic isoferritins and release them into circulation. However, there is no acidic ferritinemia not accompanied by basic ferritinemia. Therefore, the commercial assay for basic isoferritin currently seems sufficient for clinical prognostic purposes.

Effect of phytohaemagglutinin on the synthesis and secretion of ferritin in peripheral blood lymphocytes

Stimulation of lymphocytes with phytohaemagglutinin (PHA) causes an increase in the rate of ferritin and total protein synthesis which is not enhanced by supplementing the medium with iron. There is an increase in intracellular ferritin content which is amplified by the presence of iron but this is also observed in the absence of PHA stimulation. The increased cellular ferritin is greater for heart type ferritin than for spleen type ferritin. Ferritin secreted into the medium from the cells shows a relative preponderance of spleen type ferritin compared to the intracellular protein. The data shows a dissociation between ferritin synthesis, cellular accumulation and secretion for which the mechanisms have still to be elucidated.

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.

Stability of radioiodinated ferritin

Ferritin which had been radioiodinated using chloramine T exhibited marked instability on storage at 4 degrees C. Both [125I]human liver and heart ferritins showed a similar rate of decline in immunoreactivity (t 1/2 = 20-23 days) indicating that deterioration with storage was not a function of isoferritin composition. The decrease in radioactivity associated with ferritin was due not only to loss of 125I from the molecule but also to protein degradation as shown by enzyme-linked immunoassay and gel filtration. The degradation products had an Mr of at least 69,000 although low Mr material could be identified by gel filtration when a marked reduction in immunoreactivity had occurred. Ferritin instability was much more pronounced than when other proteins such as immunoglobulin and albumin were radioiodinated with chloramine T. These observations indicate that when performing in vivo and in vitro studies with labeled ferritin, degradation of the protein during storage should be carefully monitored and the protein repurified before use.

Changes in sample isoferritin composition as a possible cause of dilutional discrepancies in ferritin 2-site immunoradiometric assay results

The effect of changes in sample isoferritin composition on the behaviour of ferritin 2-site immunoradiometric assays was investigated using a computer model and experimental studies. Modelling studies predicted that under conditions where a sample has a different isoferritin composition from the assay standards, progressively higher values will be generated for the apparent ferritin content of the sample when it is analysed at increasing dilutions. In addition, the assay results will underestimate the actual ferritin content of such samples at all dilutions. Dilutional discrepancies in assay results and underestimation of sample ferritin concentrations were found in practical assays when synthetic samples with demonstrably different isoferritin profiles were analysed. Differences in isoferritin composition between assay standards and assayed samples may therefore be a cause of dilutional discrepancies in some results from ferritin 2-site immunoradiometric assays.

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.

Use of a monoclonal antibody against human heart ferritin for evaluating acidic ferritin concentration in human serum

Immunoassays for acidic ferritins rich in H subunits have shown that these isoferritins are predominant in some cells such as monocytes and red blood cells but have provided conflicting results about their presence in human serum. We have used an immunoradiometric assay based on a monoclonal antibody against human heart ferritin (monoclonal 2A4) for evaluating acidic ferritin concentration in human serum. This assay proved to be highly specific for acidic isoferritins having more than 60% H subunits. Heart-type ferritin was detected in only one fifth of normal sera and sera from patients with iron overload; values were very low compared with those for basic ferritin. Acidic ferritin was found in relatively high concentrations in most patients with iron deficiency anaemia. In other disease states characterized by increased serum concentrations of basic ferritin, acidic ferritin was always less than 21% of the total ferritin. Dialysis in low-ionic-strength buffer showed that both normal and pathological sera had binding factors for human heart ferritin. We conclude that: (i) human serum contains low concentrations of acidic isoferritins which, at variance with basic ferritin, do not appear to be directly related to the amount of storage iron; (ii) the findings of the present study reinforce the opinion that basic and acidic ferritins have different functional behaviours.

Assignment of human ferritin genes to chromosomes 11 and 19q13.3----19qter

Extracts of hamster-human and mouse-human hybrids, some with translocations involving chromosome 19, have been assayed for both human spleen ferritin (rich in L subunits) and human heart ferritin (rich in H subunits). Hybrid lines retaining part of the long arm of chromosome 19 including the region 19q13.3----19qter produced human "L" type ferritin. This confirms the previous assignment of the "ferritin gene" to chromosome 19 (Caskey et al. 1983). However, lines retaining chromosome 11 were found to contain human "H" type ferritin suggesting that the gene for the "H" subunit is on this chromosome. The presence of chromosome 6 was not necessary for the expression of either "H" or "L" type human ferritin. It thus seems unlikely that the gene for idiopathic haemochromatosis is a ferritin gene.

Differential effect of isolated placental isoferritins on in vitro T-lymphocyte function

The effect of isoferritins isolated from human term placenta on certain T-lymphocyte parameters was studied in vitro using normal human lymphocytes. These isoferritins differed in ion exchange affinity, isoelectric point, and subunit composition. Only the acidic isoferritins caused a marked suppression of phytohaemagglutinin (PHA) blastogenesis and the most acidic isoferritin ('Acid I') was suppressive at a concentration as low as 0.25 microgram/ml. All four isoferritins suppressed concanavalin A (Con A) blastogenesis in a similar concentration dependent manner, with maximum effect at an isoferritin concentration of 1 microgram/ml. Both basic and acidic isoferritins reduced the Con-A-capping phenomenon in normal lymphocytes at concentrations higher than 0.5 microgram/ml, but at 0.25 microgram/ml only the acidic isoferritin was effective. The above findings support our previous report concerning the suppressive effect of splenic ferritin on T-lymphocyte function in vitro and indicate that acidic isoferritins, which often predominate in malignancy, demonstrate a higher degree of immunosuppressive activity. Thus, acidic isoferritins may play a role in the development of abnormal lymphocyte function encountered in certain proliferative disorders.

Isolation and fractionation of ferritin from human term placenta--a source for human isoferritins

A method for isolating ferritin from human term placenta was described. The placenta was homogenized in water containing protease inhibitor and heated at 70 degrees C. The ferritin was precipitated with ammonium sulfate at pH 5.2 and purified by repeated cycles of ultracentrifugation and molecular sieve chromatography through Sepharose 4B columns. Isoelectric focusing revealed a broad spectrum of isoferritins. These isoferritins were separated by ion-exchange chromatography on Sephadex A-25 at pH 7.5 and stepwise elution with increasing concentrations of NaCl. By this method "basic," "intermediate," and "acid" isoferritins were separated. The most basic placental isoferritin was shown to be identical to splenic ferritin by isoelectric focusing, subunit analysis, and fluorescent ELISA. The acid placental isoferritin had similar characteristics to heart-type ferritin. It was suggested that the easily available placental tissue could serve as a source for human isoferritins in research and in clinical assays.

A single-step immunoradiometric assay for the measurement of serum ferritin

An immunoradiometric assay (IRMA) which can be carried out in a single working day is described here. The assay is comparable to the conventional IRMA with respect to both sensitivity and reproducibility and is less labour intensive.

Serum ferritin and malignant tumours

Increased concentrations of serum ferritin are common in patients with malignant disease and appear to be a non-specific response. The present evidence does not suggest that serum ferritin assay is useful either for specific diagnosis or monitoring of malignant disease. A special role for acidic isoferritins in malignancy remains to be substantiated.

Antigen binding in the two-site immunoradiometric assay for serum ferritin: the nature of the hook effect

The two stages of a two-site immunoradiometric assay were investigated separately. In the first stage, the amount of ferritin bound to coated tubes initially showed a rapid increase with increasing concentration of added ferritin. This was followed by a plateau and then a further increase which appeared to be largely due to non-specific binding. During the second stage, a significant proportion of the bound ferritin dissociated from the solid phase and sequestered some of the labelled antibody in solution. Thus less antibody was available to bind to ferritin attached to the tube, causing a decrease in count rate at high ferritin concentrations. The use of a monoclonal antibody for coating the tubes did not eliminate this hook effect.

Biochemical and immunological characteristics of ferritin from HL-60, U-937 and K-562 cell lines: Implications for haemopoietic regulation

It has been suggested that acidic isoferritins play a major role in the regulation of human granulocyte-macrophage (CFU-GM) proliferation. Such regulatory isoferritins are said to occur in some human tissues including both leukaemic and normal leucocytes, and certain established cell lines. They are glycosylated and bind to Con A. Extracts from HL-60, U-937 and K-562 cell lines are said to contain inhibitory activity but only in HL60 cells is the activity neutralized by antibody to acidic isoferritins. The properties of ferritin from these cell lines have been investigated. HL60 and U-937 extracts contained predominantly basic (spleen-type) isoferritins and K-562 extracts predominantly acidic (heart-type) isoferritins on immunoradiometric assay. None of the ferritin bound to Con A. On anion exchange chromatography ferritin from U-937 was basic in character, that from K-562 was acidic and HL-60 contained a variety of isoferritins. The identification of glycosylated acidic isoferritins as inhibitors of granulopoiesis appears to be an oversimplification and the classification of isoferritins on the basis of two subunit types may also need revision.

Accumulation and release of isoferritins during incubation in vitro of human peripheral blood mononuclear cells

Ferritin concentration has been measured in peripheral blood mononuclear cells and in the incubation medium following in vitro culture. Antibodies to both heart and spleen ferritin were used. Mononuclear cells cultured in medium containing about 12 mumol Fe/l accumulate ferritin rapidly with an increase in the heart:spleen ferritin ratio from 3:1 to about 10:1. Higher concentrations of iron (100 mumol/l) produce an even greater effect. The accumulation of ferritin is prevented by the addition of desferrioxamine (2 mmol/l) to the incubation medium. Accumulation of ferritin appears to take place largely in monocytes. Phagocytosis of red blood cells also causes rapid accumulation of ferritin but without any change in the heart:spleen ratio. Small amounts of both spleen and heart type ferritin are released during incubation in an iron containing medium and following phagocytosis of red blood cells. Some concanavalin A binding ferritin is also released suggesting that phagocytic cells may be a source of the concanavalin A binding ferritin found in normal plasma.

Turnover and tissue uptake of rabbit ferritin from rabbit plasma

Using a two-site immunoradiometric assay for rabbit liver ferritin normal NZW rabbits were found to have very low plasma ferritin concentrations (less than 4 micrograms/l). Purified preparations of rabbit liver and kidney ferritin were labelled with 125I and injected into rabbits. Clearance from plasma was extremely rapid with an initial half-life of 1-2 min as measured by immunoprecipitation of labelled ferritin. The rate of clearance was unaffected by the labelling procedure and by the method of ferritin purification. Autoradiography and organ uptake studies showed that 125I-rabbit liver ferritin was removed mainly by liver reticuloendothelial cells, although on a weight basis, spleen had the greatest radioactivity. These studies indicate that rabbit ferritin released into the circulation is promptly cleared by the RES.

Isoferritins in normal leucocytes

Monocytes, lymphocytes and polymorphs were separated from the peripheral blood of normal human subjects. Ferritin concentrations were determined with antibodies to both human spleen and heart ferritins. The heart type ferritin concentration in monocytes was 38.4 +/- 21.6 fg/cell (mean +/- SD), in lymphocytes 8.6 +/- 6.6 fg/cell and in polymorphs 3.2 +/- 2.4 fg/cell. Spleen type ferritin concentrations (fg/cell) were 15.6 +/- 7.0 in monocytes, 6.6 +/- 5.7 in lymphocytes and 7.0 +/- 4.6 in polymorphs. The mean heart/spleen ferritin ratios were 2.8/1 for monocytes, 2.0/1 for lymphocytes and 0.6/1 for polymorphs. The cell extracts were also subjected to anion exchange chromatography. Heart type ferritin eluted at a higher chloride ion concentration than spleen type ferritin. Both H and L subunits were synthesized by mononuclear cells when incubated with 3H-leucine. Human leucocytes contain a wide range of isoferritins and ferritin concentrations may be considerably underestimated in conventional assays for serum ferritin which employ antibodies to liver or spleen ferritin.

Turnover of 131I-human spleen ferritin in plasma

Human spleen ferritin was labelled with 131I and injected into two normal men. The labelled ferritin left the plasma rapidly. The experimental clearance curve could be fitted with accuracy into two single exponential functions. The first component, T 1/2 = 9 min, accounted for the clearance of about 90% of the labelled ferritin. Surface counting showed uptake of 131I by the liver but not by the spleen. Such a rapid plasma turnover is similar to that found after injection of tissue ferritins into experimental animals but contrasts with the slow turnover previously found for 131I-labelled human plasma ferritin. Differential clearance of isoferritins from the plasma is an important factor explaining the biochemical and immunological differences between tissue and plasma ferritins.

Ferritin synthesis in rat L-6 cells: response to iron challenge

The short term response of the L-6 cell line of rat skeletal myoblasts to elevated extracellular iron concentrations was studied. It was found in all cases that iron as the nitrilotriacetate (NTA) chelate was effective at donating iron to the cells and at stimulating ferritin synthesis. After 48 h in 50 microM ferric NTA, the cellular ferritin levels rose from an undetectable level to 1.11 (+/- 0.07) ng ferritin/microgram cell protein, or 0.1% of total cell protein. Similarly, the total iron in the cells rose under the same conditions from an unmeasurable level to plateau at over 10 fmol iron/cell. In addition, it was found that these cells synthesize ferritin in response to iron in a dose-dependent manner over a range of iron concentrations from 5-1000 microM. A sensitive and specific immunoradiometric assay for rat ferritin was used in these studies to quantitate ferritin in cell lysates.

Enrichment of erythroblasts from human bone marrow using complement-mediated lysis: measurement of ferritin

Sequential lysis of human bone marrow cells with a monoclonal antibody directed against myeloid cells (TG1) and a rabbit antiserum raised against peripheral blood mononuclear cells gave preparations in which 78-97% of the nucleated cells were erythroid, with a 24-77% recovery. Viability was high, morphology was good and the cells were able to divide and differentiate in culture. No metabolic experiments were carried out but the ferritin content of the erythroblasts was measured in four experiments and found to be about 200-2000 times higher than that found in normal erythrocytes. The H/S ratio was high in both erythroblasts and erythrocytes. Fractionation on the basis of density of two erythroblast preparations, one from a patient with sideroblastic anaemia and one from a patient with megaloblastic anaemia, showed that the most immature erythroblasts contained the highest content of ferritin and that this fell with maturation. The H/S ratio stayed the same or fell with maturation. It was concluded that this method would be valuable for the study of the role of erythroblast ferritin in normal and pathological situations.

Human ferritin: effects of antigen source and fixation on leucocyte staining by immunoperoxidase technique

The localization of ferritin was studied in peripheral blood cells and variously fixed tissues with the antibodies against ferritins isolated from human heart and spleen. The unlabelled antibody enzyme method (PAP) was used to detect the binding sites of antibodies. In peripheral blood cell smears both antisera gave rise to strong staining of polymorphonuclear (PMN) cell cytoplasm, whereas the monocytes stained relatively weakly. There were no staining differences between the two antisera. In human spleen sections the spleen ferritin antiserum stained the PMN cells and sinusoidal lining cells, whereas the heart ferritin antiserum stained only PMN cells. Neither of the two antisera stained monocytes in the spleen sections. This finding was observed in specimens fixed in Bouin's fixative, Baker's fixative and neutral formalin. However, the immunoreactivity of ferritin was totally destroyed by some other fixatives (Carnoy's fixative, formol sucrose and glutaraldehyde). These results suggest that ferritin is more readily released from monocytes than from PMN cells, and that mature spleen macrophages contain antigenic determinants of ferritin that are recognized only by anti-spleen ferritin antiserum.

Basic isoferritin and hypercalcaemia in renal cell carcinoma

A 63-year-old man with iron loss anaemia and hypercalcaemia was found to have a renal cell carcinoma. Despite the iron-deficient blood and bone marrow picture, the serum ferritin concentration was markedly raised. This was mainly due to a "basic isoferritin". The serum parathormone concentration was normal. The serum ferritin and calcium concentrations returned to normal after the tumour was removed. We propose that the renal cell carcinoma cells in this patient secreted the basic isoferritin as well as humoral factor(s) responsible for hypercalcaemia.

Detection of a glycosylated subunit in human serum ferritin

Ferritin was purified from the serum of two patients with idiopathic haemochromatosis. The protein contained three types of subunit--the H and L subunits of tissue ferritins (although only a trace of H could be detected) and a third subunit, 'G', with the highest apparent molecular weight. Only the 'G' subunit band stained for carbohydrate, indicating that a proportion of the subunits of human serum ferritin are glycosylated. Although serum was obtained from patients with idiopathic haemochromatosis, it is probable that the 'G' subunit is a component of normal serum ferritin.

Ferritin polymers and the formation of haemosiderin

When ferritin is isolated from Chang liver cells in culture iron loading is found to be associated with changes in the surface of the protein shell characterized by a change in immunoreactivity to anti "heart' and anti"spleen' antibodies at each specific pI and an overall shift in isoferritins to a lower pI range (Hoy & Jacobs, 1981). Ferritin polymers have been isolated from human tissues and their biochemical properties assessed in terms of these surface changes and the iron/protein ratio of the molecules. The results suggest that changes in the surface of ferritin molecules are associated with the formation of stable polymers. These are precursors of clumps of ferritin and eventually haemosiderin. Changes in the surface of the molecule may provide a signal for polymerization and incorporation of the protein within the lysosomes.

Ferritin synthesis in inflammation. II. Mechanism of increased ferritin synthesis

The mechanism of increased ferritin synthesis in inflammation was studied in rat livers 0-48 h after turpentine injection. A subcellular protein synthesizing system was employed in which the respective roles of cell sap factors and polysomes from normal and treated animals could be studied. Two waves of increased ferritin synthesis were found, an early wave with peak activity at 6 h of inflammation, and a second wave starting at about 24 h. The early wave of enhanced ferritin synthesis was associated with increased activity of cell sap factors. In contrast, the late enhancement of ferritin synthesis was characterized by increased polysomal activity as well as increased cell sap activity. These observations suggest a post-transcriptional control mechanism for the early phase of enhanced ferritin synthesis in inflammation, and a transcriptional as well as post-transcriptional control for the late phase of enhanced ferritin synthesis.

Ferritin concentration in normal and abnormal erythrocytes measured by immunoradiometric assay with antibodies to heart and spleen ferritin and Mössbauer spectroscopy

Immunoradiometric assays using antibodies to spleen and heart ferritin were combined with Mössbauer studies on normal and pathological erythrocytes. All erythrocytes examined were found to contain greater amounts of heart type than spleen type ferritin. The ferritin concentration in erythrocytes from patients with beta thalassaemia, sickle cell disease and sideroblastic anaemia is much higher than in normal cells. When the concentration of ferritin-like iron in the pathological erythrocytes measured by Mössbauer spectroscopy is compared to the total amount of ferritin assayed by the two antibodies in the same haemolysates the iron/protein ratio ranges between 0.3 and 3.4. The iron/protein ratio in iron-filled ferritin molecules is about 0.56 and values in excess of this suggest that the iron detected in these cells is a mixture of ferritin molecules, partly denatured ferritin polymers and 'haemosiderin'. There is a possibility that erythrocytes contain an immunologically distinct type of ferritin that is not detected by existing assays, but we have no direct evidence for this.