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PubMed2002

Multivalent metal-induced iron acquisition from transferrin and lactoferrin by myeloid cells.

We previously described a unique, high-capacity, ATP-independent mechanism through which myeloid cells acquire Fe from low-m.w. chelates. The rate of this Fe acquisition is markedly increased by cellular exposure to multivalent metal cations. Because most Fe in vivo is bound to transferrin or lactoferrin, we examined whether this mechanism also contributes to myeloid cell acquisition of Fe from transferrin and/or lactoferrin. Using HL-60 cells as a model system, we show cellular acquisition of (59)Fe from both lactoferrin and transferrin that was unaffected by conditions that depleted the cells of ATP or disrupted their cytoskeleton. Fe acquisition was dramatically increased by cell exposure to various metals including Ga(3+), Gd(3+), Al(3+), Fe(3+), La(3+), Zr(4+), Sn(4+), Cu(2+), and Zn(2+) by a process that was reversible. Exposure to these same metals also increased binding of both transferrin and lactoferrin to the cell surface by a process that does not appear to involve the well-described plasma membrane receptor for transferrin. Approximately 60% of the Fe acquired by the cells from transferrin and lactoferrin remained cell associated 18 h later. HL-60 cells possess a high-capacity multivalent metal-inducible mechanism for Fe acquisition from transferrin and lactoferrin that bears many similarities to the process previously described that allows these and other cell types to acquire Fe from low-m.w. Fe chelates. The biologic importance of this mechanism may relate to its high Fe acquisition capacity and the speed with which it is able to rapidly adapt to the level of extracellular Fe.

Adenosine Triphosphate↗

PubMed2006

[Experimental study of transferrin receptor molecular imaging in human hepatocellular carcinoma transplanted in nude mice].

OBJECTIVE: To investigate the feasibility of (99m)Tc-transferrin ((99m)Tc-Tf) as an transferrin receptor imaging agent in nude mice bearing human hepatoma SMMC-7721 tumor. METHODS: Biodistribution of (99m)Tc-Tf in Balb/c mice was assayed, and transferrin receptor imaging in Balb/c nu/nu nude mice bearing human hepatocellular carcinoma SMMC-7721 xenografts was carried out, with or without inhibition of transferrin receptor with unlabeled transferrin. The receptor radioligand binding assay with (125)I-transferrin as ligand was established, and the number of receptors per cell and the K(d) were worked out. RESULTS: (99m)Tc-Tf was mainly distributed in the liver, blood and kidneys. At 18 h post injection, the ratios of tumor/blood, tumor/liver and tumor/muscle were 24.2, 1.7 and 35.5, respectively. The ratio of tumor uptake at 18 h without unlabeled transferrin pretreatment to that with pretreatment was 16.3. The number of receptors per cell was 2.4 x 10(5) and the K(d) was found to be 4.46 nmol/L. CONCLUSION: All those results indicate that (99m)Tc-Tf is specifically localized in tumor lesions of nude mice. (99m)Tc-Tf may be useful in detection of hepatocellular carcinoma.

Animals↗

PubMed2006

Luteinizing hormone-releasing hormone agonist and transferrin functionalizations enhance nanoparticle delivery in a novel bovine ex vivo eye model.

PURPOSE: To determine whether topical ocular delivery of <100 nm nanoparticles can be enhanced by coating their exterior with peptide or protein ligands for cell surface receptors. METHODS: A novel ex vivo bovine eye model was validated for its integrity up to 60 min. Using this model, the uptake of 20 nm polystyrene nanoparticles (administered as a single 50 mul drop) before and after surface conjugation with deslorelin, a luteinizing hormone-releasing hormone (LHRH) agonist, or transferrin was determined at 5 and 60 min in individual layers of cornea and aqueous humor. Selected studies were done in the absence of corneal epithelium in the ex vivo model or using excised cornea and conjunctiva. LHRH and transferrin receptor mRNA and protein expression in corneal epithelium and conjunctiva were determined by real-time PCR and western blot, respectively. RESULTS: Corneal histology, ZO-1 immunostain pattern, and mannitol permeability were similar in controls and at the end of the ex vivo study. Corneal epithelial nanoparticle uptake in the absence of surface modification was 1.1-1.6% at 5 min and remained at about this level even at 60 min. Removal of the corneal epithelium resulted in about 22% particle uptake in the corneal stroma at 5 and 60 min compared to about 0.5% in the presence of epithelium, indicating the barrier nature of corneal epithelium. Deslorelin and transferrin conjugation enhanced corneal epithelial uptake of nanoparticles by 3- and 4.5 fold at 5 min and by 4.5- and 3.8 fold at 60 min, respectively. The total corneal uptake in 5 min is approximately 2.4, 9, and 16% with plain, deslorelin-functionalized, and transferrin-functionalized nanoparticles. In all groups, the nanoparticle uptake per unit tissue weight was in the order: corneal epithelium>stroma>endothelium with levels in the aqueous humor being undetectable. In excised cornea and conjunctiva studies, nanoparticle transport and uptake was elevated for both deslorelin and transferrin conjugated nanoparticles. Expression of LHRH and transferrin receptors was observed in corneal epithelium as well as conjunctiva. CONCLUSIONS: The ex vivo bovine eye model is a useful tool in understanding disposition of nanoparticles after topical delivery. The corneal epithelium is a significant barrier for topical nanoparticle delivery to the anterior segment. Surface modification of nanoparticles by conjugating an LHRH agonist or transferrin is a useful approach to provide rapid, efficient delivery of intact nanoparticles into and/or across cornea and conjunctiva.

Animals↗

PubMed1991

Transferrin receptor expression in normal and iron overloaded liver.

Hepatocytes take up transferrin-bound iron by two mechanisms. One pathway consists in the binding of transferrin to high affinity receptor sites. This process results in receptor-mediated endocytosis and is highly efficient and saturable. The other mechanism involves low affinity, non-specific and non-saturable internalization of transferrin-bound iron, probably through pinocytosis, adsorptive endocytosis or low affinity binding sites. At low transferrin saturation, the first mechanism is quantitatively most important, at high transferrin saturation the latter mechanism becomes more significant. A mechanism whereby transferrin-bound iron is not endocytosed but reduced at and translocated through the plasma membrane has also been invoked and challenges the concept of (receptor-mediated) endocytosis of transferrin. However, this hypothesis remains to be confirmed.

Animals↗

PubMed1990

Phorbol ester-induced macrophage-like differentiation of human promyelocytic leukemia (HL-60) cells occurs independently of transferrin availability.

Human promyelocytic leukemia (HL-60) cells can be induced to differentiate into macrophage-like cells by the tumor-promoting phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). Addition of this agent to HL-60 cells causes a rapid internalization of surface transferrin receptor, followed by long-term receptor down-regulation at the level of gene expression. These effects precede the inhibition of proliferation and the acquisition of differentiation markers, and it has been suggested that transferrin receptor down-regulation may play a mediating role in these later events. Here we show that HL-60 cells will grow indefinitely in serum-free medium supplemented with either 5 micrograms ml-1 transferrin or 300 microM ferric citrate and that TPA inhibits cell proliferation (assayed by cell density and rate of thymidine incorporation) and induces macrophage-like differentiation (assayed by induction of cell adhesion and increased nonspecific esterase activity) with identical dose curves in both media. Furthermore, a neutralizing anti-transferrin antibody completely inhibits transferrin-dependent cell proliferation but has no effect on differentiation in the presence or absence of transferrin. We conclude that TPA-induced down-regulation of transferrin binding and internalization does not mediate the subsequent growth arrest and differentiation of HL-60 cells.

Cell Differentiation↗

PubMed1990

Differential expression of a Mr approximately 90,000 cell surface transferrin receptor-related glycoprotein on murine B16 metastatic melanoma sublines selected for enhanced brain or ovary colonization.

A cell surface Mr approximately 90,000 glycoprotein (gp90) was found in higher amounts on brain-colonizing than on lung-colonizing murine B16 melanoma sublines. The possible role of gp90 in determining the brain-associated metastatic properties of B16 cells was examined by purifying the glycoprotein and studying the effects of anti-gp90 on the growth, adhesion, and organ colonization properties of B16 cells. The specificity of the anti-gp90 was demonstrated in immunoprecipitation studies where a cell surface- or metabolically labeled Mr approximately 90,000 glycoprotein of pI approximately 4 was exclusively found upon two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. Immunoprecipitation analysis, enzyme-linked immunosorbent assays, and the lectin-binding properties of gp90 on lectin affinity columns indicated that it is a Mr approximately 180,000 disulfide-linked dimer, probably related to the transferrin receptor. B16 sublines selected for various organ colonization properties differentially expressed gp90, bound 125I-labeled transferrin, and responded differently to purified transferrin in proliferation assays in relation to their metastatic properties (B15b greater than O13 greater than F10 greater than F1). Anti-gp90 immunoglobulin G affected the growth of brain-colonizing B16-B15b more than B16-F1 cells, but had no effect on the adhesion of B16-B15b or -F1 cells to microvessel endothelial cells in vitro, and anti-gp90 immunoglobulin G F(ab')2 had little effect on the brain colonization properties of B16-B15b cells in syngeneic mice. In blocking assays, anti-gp90 inhibited the binding of 125I-labeled transferrin to B16-B15b cells in a dose-dependent manner. The results suggest that the differential growth-stimulating effects of transferrin on highly metastatic B16 melanoma cells may be due to their differential expression of a Mr approximately 90,000 glycoprotein that is related to the transferrin receptor. In organ sites, such as the brain, differential expression of a transferrin-like receptor may allow metastatic cells to respond to low concentrations of growth factors known to be present in certain organs.

Animals↗

PubMed1985

Characterization of a transferrin-diphtheria toxin conjugate.

We report here the synthesis and properties of a hybrid toxin prepared by covalently coupling diphtheria toxin to transferrin. The purified material contained two major hybrid protein species and was highly cytotoxic to mouse LMTK- cells in culture, reducing protein synthesis by 50% in 24 h at a concentration of 1 ng/ml. Cytotoxic activity was completely abolished in the presence of exogenous transferrin or anti-transferrin or anti-diphtheria toxin, thus demonstrating that the hybrid toxin was intoxicating cells via their transferrin receptors and that both the diphtheria toxin and transferrin components of the conjugate were necessary for activity. NH4Cl, a drug that elevates the pH within acidic intracellular vesicles, also blocked cytotoxic activity, suggesting that a low intravesicular pH was required for activity. The inhibitory effect of NH4Cl could be abolished by exposing toxin-treated cells to acidic culture medium, further implicating an acid-dependent step in the mechanism of the hybrid toxin action. Studies on the kinetics of intoxication also implied that endocytosis and exposure to a low pH within vesicles were necessary for cytotoxicity. Altogether, the results suggest that the transferrin-diphtheria toxin conjugate binds to transferrin receptors and is internalized into acidic endocytic vesicles. The enzymatic moiety of diphtheria toxin then apparently enters the cytosol in response to the low pH and subsequently arrests protein synthesis.

Ammonium Chloride↗

PubMed1985

Inhibition of transferrin receptor expression by interferon-alpha in human lymphoblastoid cells and mitogen-induced lymphocytes.

125I-Transferrin binding to lymphoblastoid K562 and Daudi cells markedly increased after exposure of the cells to culture conditions that stimulated proliferation. Treatment of these cells with interferon-alpha (IFN-alpha) resulted in concurrent inhibition of cell growth and of the rise in transferrin binding. Scatchard analyses revealed that IFN reduced the number of transferrin receptors without altering the binding constant. When 125I-transferrin binding was measured using permeabilized cells, the IFN-induced reduction of binding was comparable to that observed with intact cells, indicating that IFN diminished the total number of cellular transferrin receptors. We also found that addition of IFN-alpha to phytohemagglutinin-stimulated human lymphocytes inhibited the mitogen-induced enhancement of [3H]thymidine incorporation as well as surface binding of 125I-transferrin. Our findings suggest that the decrease in transferrin receptor expression on IFN-alpha-treated cells may be one of the mechanisms responsible for the antiproliferative action of IFN.

Cell Division↗

PubMed1984

NK recognition of target structures: is the transferrin receptor the NK target structure?

That the transferrin receptor acts as a target antigen for human NK cells has previously been suggested. In this study we used two models to examine the hypothesis that the transferrin receptor is recognized by NK cells. In the first model, we employed mouse cloned NK cells in conjunction with the species-specific monoclonal antibody R17 217, which binds to the murine transferrin receptor. We show that there is no correlation between the amount of transferrin receptor expressed on targets and the susceptibility of these targets to NK lysis or NK binding in cold target competition assays. In the second model, we used human NK cells and transferrin receptor-positive transformants as targets. These transformants were derived from mouse L cells transfected with human DNA and selected for the presence of human transferrin receptor. Results show that, in contrast to the mouse system, there is a correlation between the expression of the human transferrin receptor on targets and the ability of these targets to competitively inhibit the lysis of K562 by NK cells. However, because inhibition is not complete, other cell surface antigens probably play a role in human NK-target interactions.

Animals↗

PubMed1993

Differences among various lineages of antigen-presenting cells in processing exogenous antigen internalized through transferrin receptors.

The Ag, pigeon cytochrome c, was coupled to human ferric transferrin by a heteroligation technique to target Ag into the endosomal transport pathway via transferrin receptors. The ability of various types of APC that do or do not express transferrin receptors to process exogenous Ag in their endosomes was investigated by the stimulation of Ag-specific CD4+ T cells with the transferrin-Ag conjugate in a serum-free assay. When two B lymphoma cells were the source of APC, the conjugate was significantly more potent than native Ag in activating the T cells, agreeing with our previous finding using a third B lymphoma cell. The conjugate and Ag were similarly presented by splenic B cells that lack transferrin receptors to the T cells. However, both a macrophage hybridoma and a MHC class II-L cell transfectant hardly elicited a T cell response to the conjugate, although a response to native Ag was readily observed. These findings could not be attributed to an absence of transferrin receptors or receptor-mediated internalization of the conjugate, nor to differential expression of MHC class II molecules or li chain by the APC. The poor presentation of the conjugate by the L cell transfectants was associated with diminished catabolism of the conjugate, however, the macrophage hybridoma rapidly degraded the conjugate, similar to the B lymphoma cell. Peritoneal macrophages, which lack transferrin receptors, and the macrophage hybridoma induced a response to the conjugate only at concentrations that allowed internalization by fluid phase pinocytosis. The lower potency of the conjugate compared with native Ag with non-B-presenting cells suggest that these cell types process the conjugate by a different mechanism than used by B cells. Differences in the mechanism of Ag processing used by APC of distinct cell lineages may possibly influence immune responsiveness.

Animals↗

PubMed1994

The estrogen-inducible transferrin receptor-like membrane glycoprotein is related to stress-regulated proteins.

It was previously shown that estrogen induces a membrane glycoprotein (molecular mass, 95 kDa) in the chicken oviducts, which exhibits several properties similar to transferrin receptors (Poola, I., and Lucas, J. J. (1988) J. Biol. Chem. 263, 19137-19146). In the present study, we have further investigated its molecular and transferrin binding properties. We have sequenced several internal peptides isolated from the purified protein by endopeptidase Lys-C. We have found that it has a high degree of sequence homologies with those of chicken heat-shock protein (cHsp108), mouse endoplasmic reticulum protein (mERp99), hamster glucose-regulated protein (hagrp94), and human tumor rejection antigen (hTRAgp96), all of which are shown to be highly homologous to each other and to yeast hsp90. We demonstrate here that the [35S]methionine-labeled immunoaffinity-purified estrogen-inducible membrane glycoprotein binds to the transferrin affinity columns similar to iron-modulated transferrin receptors. Indirect immunofluorescence microscopic studies indicate that it is an intracellular glycoprotein unlike transferrin receptors. We have isolated two molecular forms of the protein, with molecular masses of 116 and 104 kDa, by immunoaffinity column purification, immunoprecipitation, Western blotting, and pulse-chase labeling analyses. Both 116-and 104-kDa species bind transferrin. This protein can be induced by heat-shocking the oviduct cells at 45 degrees C for 3h and recovering at 37 degrees C for 2-3 h. It is also expressed in the human breast cancer cell lines, MCF-7 and T-47D. All these properties taken together strongly suggest that the estrogen-inducible membrane glycoprotein is a novel transferrin-binding protein, structurally related to the stress-regulated proteins.

Amino Acid Sequence↗

PubMed1994

Primary receptor-recognition site of human transferrin is in the C-terminal lobe.

The role of the transferrin receptor in capturing and conveying transferrin through the cell during the iron-donating cycle of receptor-mediated endocytosis has been studied extensively. Nevertheless, almost nothing is known of how human transferrin binds to its receptor. In an initial approach toward delineating the receptor-recognition site(s) of human transferrin, we have studied the interactions of proteolytically-cleaved, single-sited fragments of transferrin, representing the N- and C-lobes of the molecule respectively, with cells expressing the transferrin receptor on their plasma membranes. Only the C-fragment was found capable of donating iron to hepatoma-derived HuH-7 cells or of binding to surface receptors of HuH-7 and leukemic K562 cells. Although no association of N- and C-fragments could be demonstrated by gel chromatography, the presence of excess N-fragment strengthened the binding of C-fragment by an order of magnitude. An explanation of these observations is that the primary receptor recognition site of human transferrin is on the C-lobe of the protein, but that prior binding of this lobe to receptor enables the N-lobe to respond to receptor as well, either directly or by interaction with the bound C-lobe.

Amino Acid Sequence↗

PubMed1999

Structural studies on sugar chains of carbohydrate-deficient transferrin from patients with alcoholic liver disease using lectin affinity electrophoresis.

It is well-known that microheterogeneity of human serum transferrin observed in alcoholics manifests as sialic acid-deficient transferrin isoforms, otherwise known as carbohydrate-deficient transferrin (CDT). A recent study demonstrated that serum CDT lacked one or both of the entire carbohydrate chains but the investigation required several troublesome procedures. The aim of the present study was to confirm the sugar chain structures of serum transferrin, and of serum CDT in particular, from patients with alcoholic liver disease (ALD) using conventional lectin affinity electrophoresis which might be useful in the clinical setting. The serum CDT obtained from ALD-patients was partially purified using an anion exchanger. Serum transferrin and the partially purified serum CDT were investigated by concanavalin A (Con A)- and Datura stramonium agglutinin (DSA)-affinity electrophoresis followed by antibody-affinity blotting and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with Western blotting. By Con A-affinity electrophoresis, serum CDT was separated into weakly reactive and nonreactive transferrins which showed slower electrophoretic mobilities than those from the healthy controls. Moreover, nearly all of the serum CDT was nonreactive with DSA. On SDS-PAGE, the molecular masses of serum CDT were estimated to be approximately 75 and 72 kDa, which corresponded to those of partially and completely deglycosylated transferrin obtained from the healthy controls (78 kDa), respectively. In conclusion, these results indicated that the sugar chain structures of serum CDT from patients with ALD show not merely a loss of terminal sialic acids, but also the absence of asparagine-N-linked oligosaccharides.

Antibody Affinity↗

PubMed1990

Prognostic importance of serum transferrin and ferritin in childhood Hodgkin's disease.

The relationship of iron-binding proteins to prognosis was studied in 50 children at the Children's Hospital of Philadelphia, newly diagnosed with Hodgkin's disease (HD). There were five patients with Stage I, 18 with Stage II, 14 with Stage III, and 13 with Stage IV. Initial serum ferritin, transferrin, iron, hemoglobin (Hb), erythrocyte sedimentation rate (ESR), and A or B symptoms were analyzed for their association with progression-free survival (PFS). There was a linear increase of mean and median ferritin levels and a decrease of mean and median transferrin levels with advancing stages. Also, there was a significant inverse correlation between ferritin and transferrin (P less than 0.001). In univariate analyses, high ferritin (greater than 142 ng/ml) (P = 0.02) and low transferrin (less than or equal to 250 mg/dl) (P = 0.008) were significantly associated with poor PFS. Serum iron, Hb, ESR, and A or B symptoms were not associated with PFS. Stepwise proportional hazards regression analysis of all factors showed that transferrin was the only factor significantly associated with PFS. These preliminary results suggest that serum transferrin can also be used as a prognostic factor in addition to serum ferritin and that it may be helpful to assay both serum ferritin and transferrin as prognostic factors in childhood HD. Further testing of large groups of patients is needed to determine whether they are independent of tumor bulk and other established prognostic factors.

Adolescent↗

PubMed1993

Decreased affinity and number of transferrin receptors on erythroblasts in the anemia of rheumatoid arthritis.

In anemia of chronic disease (ACD) in rheumatoid arthritis (RA) a decreased iron uptake and transferrin binding by erythroblasts are postulated to play a pathophysiological role. To examine whether this is related to changes in transferrin receptor expression by erythroblasts, we studied bone marrow from 5 healthy controls, 5 nonanemic RA patients, and 9 RA patients with ACD. Bone marrow mononuclear cells were incubated with increasing concentrations of 125I-transferrin and specific binding data were analyzed by the method of Scatchard. The number of transferrin receptors on erythroblasts from RA patients with ACD was significantly lower as compared to nonanemic RA patients (P < .05) and controls (P < .02). The affinity of the transferrin receptor tended to be lower in ACD. These preliminary data may indicate that transferrin receptor expression by erythroblasts is impaired in ACD. Since the rate of erythroid iron uptake is mainly determined by the number of transferrin binding sites, this may explain a decrease in erythroblast iron availability in ACD in RA.

Aged↗

PubMed1976

Localization of transferrin on the surface of the human placenta by electron microscopic immunocytochemistry.

During the course of gestation, a large amount of iron is transferred rapidly and unidirectionally from mother to fetus across the placenta. It has been postulated that one of the first steps involved in placental iron transfer involves binding of the maternal transferrin-iron complex to the surface of the placenta and the subsequent removal of iron and release of transferrin back into the maternal circulation. To determine if transferrin is present on the surface of human placental villi, two different immunocytochemical methods have been used: (1) an unlabeled antibody, peroxidase-antiperoxidase (PAP) method utilizing rabbit antiserum to human transferrin, goat anti-rabbit IgG and rabbit peroxidase-antiperoxidase complex or; (2) a peroxidase-labeled antibody method utilizing goat antiserum to human transferrin and peroxidase-conjugated rabbit anti-goat IgG. The peroxide was then localized by incubation in a diaminobenzidine-hydrogen peroxide medium. Examination of the tissue in the electron microscope revealed the reaction product deposited as discrete patches or particles on the microvillous surface of human syncytial trophoblast. Controls using non-immune serum or an antiserum adsorbed with purified human transferrin showed no reaction product on the surface. The results provide morphological confirmation for the presence of transferrin on the surface of human syncytial trophoblast lining the maternal blood spaces.

Chorionic Villi↗

PubMed1995

Transcriptional regulation of Sertoli cell differentiation (transferrin promoter activation) during testicular development.

Previously testicular peritubular cells have been shown to produce a paracrine factor PModS that promotes Sertoli cell differentiation. This mesenchymal-epithelial cell interaction appears to regulate a number of Sertoli cell differentiated functions including transferrin gene expression. The current study was designed to identify PModS-activated response elements in the transferrin promoter and correlate this with Sertoli cell differentiation that occurs during testis development. The 3-kb transferrin promoter was digested down to approximately 200-bp fragments. Nuclear extracts from Sertoli cells stimulated with PModS were used in gel mobility shift assays. Two promoter regions located at -2.4 kb and -1.9 kb were designated SE1 and SE2. PModS promoted the presence of factors in Sertoli cell nuclear extracts that bind SE1 and SE2. Displacement studies demonstrated that SE1 and SE2 are distinct. A transferrin promoter-reporter construct containing these apparent response elements was activated by PModS, while a minimal transferrin promoter by 600bp excluding SE1 and SE2 was only partially stimulated by PModS. Therefore, PModS appears to in part activate the transferrin promoter through SE1 and/or SE2. Gel shift assays with Sertoli cell nuclear extracts and 20-day-old testis extracts were the same. Interestingly, the nuclear extract from a newborn testis also had a gel shift. Therefore, some of the nuclear factors stimulated by PModS in Sertoli cells and present in mid-pubertal testis were also present at birth upon completion of embryonic development. Previously transferrin expression has been shown to increase significantly at the onset of puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Possible significance of transferrin levels in seminal plasma of fertile and infertile men.

Human seminal plasma contains large amounts of transferrin, which is a protein secreted mostly by Sertoli cells. It has been suggested that the concentration of transferrin may serve as a possible clinical marker of Sertoli cell function. Therefore the concentration of this protein in human seminal plasma from fertile and infertile men has been evaluated in order to find a relationship between transferrin concentrations and human semen parameters and plasma FSH levels. Findings show that seminal transferrin in subjects with oligozoospermia or azoospermia is significantly lower than in controls, and that it is strongly related to sperm count. Results also indicate that transferrin secretion can be impaired when plasma FSH levels are still normal, suggesting that seminal transferrin is an early and specific marker of Sertoli cell function. These results, however, do not clarify whether impairment of transferrin secretion by Sertoli cells is due to an organic dysfunction or to an organic secretory alteration.

Follicle Stimulating Hormone↗