Expression of transferrin receptors on mitogen-stimulated human peripheral blood lymphocytes: Relation to cellular activation and related metabolic events (original) (raw)
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Clinical & Experimental Immunology
The transferrin receptors which appear on mitogen-activated human peripheral blood lymphocytes were found by the use of immunofluorescence techniques to display temperature-dependent patching and capping reactions upon binding of transferrin. Lateral mobility of ligand-occupied membrane sites was accompanied by both shedding and endocytosis of receptor-transferrin complexes. In the presence of sodium azide or the microfilament inhibitor cytochalasin B, cap formation and shedding were markedly inhibited. In contrast, endocytosis of patched receptor-ligand complexes was inhibited by azide and microtubule inhibitors, including colchicine, vinblastine and vincristine. Cocapping experiments performed to elucidate further the alterations in membrane configuration involved in these reactions failed to reveal any topographical relationship between transferrin receptors and lectin-binding sites in these cells. These studies indicate that temperature-dependent mobility of transferrin receptors upon mitogen-activated peripheral blood lymphocytes is dependent upon the integrity of the cytoskeletal system and metabolic function of the cell.
Transferrin binding by human lymphoblastoid cell lines and other transformed cells
Cellular Immunology, 1980
Viable cells of 18 human cell lines, including I5 transformed cell lines of malignant and lymphoblastoid origin, were examined by an indirect immunofluorescence method for their ability to bind purified transferrin and transferrin in normal human serum. The specificity of the reaction was investigated by study of the binding reactions of several other serum proteins, including albumin, c~-1-antitrypsin, and o-2-macroglobulin. Membrane binding of human transferrin was demonstrated in less than 5% of normal peripheral blood mononuclear cells or cultured diploid fibroblasts, but in more than 80% of the cells from 13 of the transformed lines, and the data obtained indicated that this binding reaction reflected the presence of specific receptors for transferrin.
A soluble form of the human transferrin receptor is released by activated lymphocytes in vitro
Clinical and Experimental Immunology, 2008
Soluble transferrin receptors (sTfR) were detected in culture supernatants of activated human peripheral blood mononuclcar cells (PBMC) using a sandwich ELISA technique with two non-cross-reacting TfR MoAbs. Mitogenic stimulation of lymphoid cells induced both up-regulation of TfR surface density and release of sTf R to the medium. Peak levels of sTfR in culture supernatants occurred at day 4 after activation, 1 day later than maximum expression of TfR in the plasma membrane. Production of sTfR was independent of proliferation, as demonstrated by measuring sTfR release by PBMC, which had becn irradiated with a dose of 20 Gy before activation. In addition to these in vitro experiments, we tested the sera of 85 patients with systemic lupus erythematosus (SLE). an autoimmune disease accompanied by in vivo activation of lymphocytes, for their sTfR levels. No correlation of these data was detectable to serum concentrations of the soluble α-chain of the IL-2 receptor, an unequivocal marker of lymphocyte activation. However, they correlated negatively to the haemoglobin content of the patients’ erythrocytes. indicating that erythroid progenitors are the predominant source of sTf R in SLE patients’ sera.
Transferrin receptors on human B and T lymphosblastoid cell lines
Biochimica et Biophysica Acta (BBA) - General Subjects, 1979
Experiments demonstrating the existence of receptors for iron-saturated transferrin on both B and T lymphoblastoid cell lines of human origin are described. Binding of '2~I-labeled transferrin is rapid, saturable and reversible. It can be specifically inhibited by unlabeled transferrin but not by other proteins. The number of receptors on T cell lines determined by Scatchard analysis is almost double the number on B cell lines but the binding affinities are equal.
Quiescent lymphocytes express intracellular transferrin receptors
Biochemical and Biophysical Research Communications, 1984
Both quiescent and concanavalin A stimulated murine splenic lymphocytes were examined for the expression of surface and intracellular binding sites for the serum glycoprotein transferrin. Transferrin binding activity was observed on the surface of mitogen stimulated cells only. When soluble detergent extracts of both populations were studied, quiescent lymphocytes were shown to contain a significant pool of non-surface exposed, intracellular receptors which was approximately 20% of the total receptor complement of proliferating cells. Because the ratio of surface to intracellular binding sites was dramatically increased following mitogen stimulation, the regulation of transferrin receptor expression during this process may involve a substantial alteration in its subcellular distribution in addition to the well documented increase in number of binding sites. Expression of cell surface receptors for the serum glycoprotein transferrin has been associated with the initiation of cell proliferation (1,2) and the significance of this relationship is supported by studies documenting a functional role for transferrin and its specific receptor in this process (3,4). In previous reports, we and others have observed a stringent regulation of cell surface transferrin receptor expression in normal lymphocytes undergoing mitogen induced proliferative responses (5,6). Thus, expression of this receptor on normal lymphocyte cell surfaces appears to be restricted to cells actively involved in DNA synthesis and cell division. Recently, studies from several laboratories have documented the existance of a substantial pool of intraeellular transferrin receptors (7,8) representing nearly 80% of the total complement of cellular binding sites. In the present communication we examined both quiescent and concanavalin A stimulated murine splenic lymphocytes with respect to the existance and size of
Identification of transferrin receptors on the surface of human cultured cells
Proceedings of the National Academy of Sciences, 1979
We have examined the binding of human transferrin to cultured human choriocarcinoma cell lines and to detergent extracts of such cells. The results indicate the presence of a high-affinity saturable binding site (Ka = 4.25 x 10(8) M-1) that is specific for transferrin. This receptor has also been detected on three other human cell lines of different phenotypic origin, including Wil-2 (splenic lymphocytes of B-cell origin), RPMI-2650 (a quasi-diploid nasopharyngeal carcinoma), and WI-38 (embryonic lung fibroblasts). By using anti-human transferrin antiserum to immunoprecipitate the receptor-transferrin complex from detergent extracts of cells containing saturating levels of transferrin followed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, a single polypeptide of 90,000 daltons has been identified as a subunit of the putative transferrin receptor. The protein shows immunochemical identity and coelectrophoreses in sodium dodecyl sulfate gels with a cell surface glycopr...