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Query: UNIPROT:P02794 (ferritin)
 17,525 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thymus-derived (T) cells obtained from three categories of in vitro antigen-induced proliferative responses were assayed as sources of helper T cells. These categories are exemplified by (a) direct stimulation of keyhole limpet hemocyanin (KLH)-primed cell with KLH, which results in high indexes of proliferation; (b) direct stimulation of apoferritin-primed cells with apoferritin, which does not result in indexes of proliferation above background levels; (c) trans-stimulation of unprimed cells with X-irradiated KLH-primed cells which results in indexes of proliferation comparable to category (a). Our results indicate that levels of [3H]thymidine incorporation by proliferating populations are not an accurate reflection of helper T cell generation. Directly stimulated KLH and apoferritin-primed cells give rise to highly enriched populations of antigen-specific helper T cells which support both IgM and IgG antibody responses in vitro. Moreover, these specific helper T cells are functionally restricted by products encoded by the I region of the major histocompatibility complex (MHC). Helper T cells generated in KLH-trans-stimulated cultures are not KLH-specific in that comparable levels of helper activity are expressed using either KLH or apoferritin as carriers. These non-KLH-specific helper T cells only support the production of IgM antibody in vitro and they are not functionally restricted by MHC products.
Eur J Immunol 1979 Sep
PMID:Helper activity of T cells stimulated in long-term culture. 9 11

Using transmission electron microscopy, we have studied the interaction of alpha 2 macroglobulin (alpha 2 M) with the surface of cultured fibroblasts. When cells were incubated for 2 h at 4 degrees C with ferritin-conjugated alpha 2 M, approximately 90% of the alpha 2 M was diffusely distributed on the cell surface, and the other 10% was concentrated in "coated" pits. A pattern of diffuse labeling with some clustering in "coated" pits was also obtained when cells were incubated for 5 min at 4 degrees C with alpha 2 M, fixed with glutaraldehyde, and the alpha 2 M was localized with affinity-purified, peroxidase-labeled antibody to alpha 2 M. Experiments in which cells were fixed with 0.2% paraformaldehyde before incubation with alpha 2 M showed that the native distribution of alpha 2 M receptors was entirely diffuse without significant clustering in "coated" pits. This indicates that some redistribution of the alpha 2 M-receptor complexes into clusters occurred even at 4 degrees C. In experiments with concanavalin A(Con A), we found that some of the Con A clustered in coated regions of the membrane and was internalized in coated vesicles, but much of the Con A was directly internalized in uncoated vesicles or pinosomes. We conclude that unoccupied alpha 2 M receptors are diffusely distributed on the cell surface. When alpha 2 M-receptor complexes are formed, they rapidly cluster in coated regions or pits in the plasma membrane and subsequently are internalized in coated vesicles. Because insulin and epidermal growth factor are internalized in the same structures as alpha 2 M (Maxfield, F.R., J. Schlessinger, Y. Schechter, I. Pastan, and M.C. Willingham. 1978. Cell, 14: 805--810.), we suggest that all peptide hormones, as well as other proteins that enter the cell by receptor-mediated endocytosis, follow this same pathway.
J Cell Biol 1979 Sep
PMID:alpha 2 Macroglobulin binding to the plasma membrane of cultured fibroblasts. Diffuse binding followed by clustering in coated regions. 9 73

Serogroups of N. meningitidis were characterized as virulent or avirulent according to their capacity to establish meningococcal infection in mice. An agar plate diffusion technique demonstrated that iron had a definite growth-supporting role for both of these meningococcal types. The avirulent strains could use ionic or chelated iron as well as the virulent strains. Iron-reversible growth inhibition occurred to the same extent for both bacterial types in the presence of the synthetic iron-chelating agents Desferal and ethylenediamine-di-orthohydroxy phenylacetic acid. A difference in response was demonstrated for these bacterial types when grown in the presence of various iron-binding proteins from animal body fluids and tissues. The growth of the avirulent strain was inhibited to a greater degree by egg white conalbumin. The humoral iron-binding protein transferrin showed a significant inhibitory capacity only when used in conjunction with bicarbonate. Under conditions of increased iron saturation of this protein, the avirulent strain was inhibited to the furthest extent. In the presence of ferritin, the cellular iron-binding protein, which had been reduced, inhibition of the growth of either strain type did not occur on iron-poor media (less than 5 micrograms/100 ml). However, with the incorporation of iron into the media, the inhibitory effect of the protein became evident. As the concentration of iron increased, the inhibition increased to a certain level and subsequently declined. A substantial difference in the ability of the avirulent type to grow in the presence of reduced horse spleen ferritin was observed. For this microorganism, a correlation appears to exist between the capacity to grow by utilizing the available iron in the presence of reduced ferritin and the ability to establish infection. The host protein ferritin, in the reduced state, apart from simply being a storage protein for iron, can prevent the growth of a procaryotic organism. Our experiments suggest a role for ferritin in the prevention of emningococcal disease. A cehmotherapeutic potential for Desferal is also implied.
Infect Immun 1979 Sep
PMID:Inhibition of the growth of Neisseria meningitidis by reduced ferritin and other iron-binding agents. 11 92

The endocytic vacuoles induced in white ghosts were found to be depleted of spectrin and therefore it was proposed that they arose from spectrin-free areas in the erythrocyte membrane. To follow changes in spectrin distribution during endocytosis, affinity-purified rabbit antispectrin antibodies were produced. Quantitative techniques were developed for the use of a highly specific 125I-F(ab')2 antispectrin, and these showed that before the appearance of vacuoles, as assessed by phase microscopy, there was a reproducible decrease in immunoreactive spectrin. To determine whether this spectrin decrease represented a local or diffuse spectrin loss or a spectrin rearrangement, morphologic studies were undertaken using transmission electron microscopy on samples treated with rabbit antispectrin and ferritin-conjugated goat anti-rabbit immunoglobulin. These studies showed that endocytosis was preceded by the creation of extensive spectrin-free areas separated by discrete spectrin-containing zones. Pretreatment of ghosts with alkaline phosphatase blocked all forms of endocytosis and prevented the creation of spectrin-free areas. Therefore, it is proposed that under the impetus of endocytosis inducers, phosphorylated spectrin is redistributed so that spectrin-free zones are created, and that endocytic vacuoles form and fuse in spectrin-free areas.
J Cell Biol 1979 Sep
PMID:Spectrin rearrangement early in erythrocyte ghost endocytosis. 11 12

The surface charge of cultured neurons was investigated with the electron microscope markers anionized ferritin (AF) and cationized ferritin (CF). To determine which membrane components could react with the markers, model reactions were used. Both protein-coated Sepharose beads and lipid vesicles were reacted at physiological pH. Results with these model reactions indicate that the following groups may contribute to the surface charge: acidic groups--the sialic acid of both glycoproteins and gangliosides, the carboxyl group of proteins, and the phosphates of phospholipids; basic groups--the amines of proteins. The effect of chemical fixation on the surface charge was investigated. Glutaraldehyde fixation was shown to increase the charge of neutral proteins but not by a mechanism involving unbound aldehydes. Glutaraldehyde fixation of phospholipid vesicles in the presence of CF showed that amine-containing phospholipids were cross-linked to CF. This cross-linkage was seen with the electron microscope as the clumping of CF and the burying of CF in the membrane. Paraformaldehyde fixation had a lesser effect on the charge of proteins but did react with phospholipids as did glutaraldehyde. It is concluded that at physiological pH: (a) most of the charged proteins and lipids on cell surface can contribute to the membrane surface charge, and (b) the membrane surface charge of cells can be greatly changed by chemical fixation.
J Cell Biol 1979 Sep
PMID:Contributions of lipids and proteins to the surface charge of membranes. An electron microscopy study with cationized and anionized ferritin. 11 15

Ferritin has been purified from normal full-term human placentae and its antigenic and molecular characteristics compared with adult liver ferritin. Placental ferritin is composed predominantly of a single subunit type, co-migrating with a liver ferritin standard on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Comparison of dose-response curves in an immunoradiometric assay indicated some tissue-specific antigenicity for placental ferritin. This was supported by immunofluorescence studies on cryostat sections of human placentae by using antibodies to placental and spleen ferritin. Specific staining for placental ferritin was demonstrated within placental syncytiotrophoblast, particularly localized towards the microvillus plasma membrane. Ferritin has also been shown by electrophoretic and antigenic analysis to be present in protein fractions solubilized from isolated human syncytiotrophoblast microvillus plasma-membrane preparations, suggesting that ferritin may play an active role in the transfer of iron from maternal transferrin across the syncytiotrophoblast plasma membrane.
Biochem J 1979 Sep 15
PMID:Characterization and localization of human placental ferritin. 11 99

Tissue tolerance was induced in neonatal rats by the intravenous injection of bone marrow cells from adult allogeneic rat donors. After 6 to 8 weeks, lymphoid cells from rats in which tolerance had been induced were tested for mixed lymphocyte reactivity (MLR), 3H-uridine uptake, and the relationship of uridine incorporation to B and T lymphocytes. Lymph node (LN) and spleen (SPL) cells from the adult inoculated rats showed no reactivity in the MLR or normal lymphocyte transfer reaction (NLTRx), indicating that the animals were tolerant. After in vitro exposure to 3H-uridine, an abundance of small lymphocytes (SL) from these same tolerant rats were heavily labeled, in contrast to nontolerant controls, where relatively few SL were heavily labeled. In order to determine whether the heavily uridine-labeled cells were T cells or B cells, lymphoid cells from the LN and SPL of tolerant animals were exposed to either rabbit anti-AKR brain serum or rabbit anti-rat Ig conjugated with ferritin. The results showed that the heavily uridine-labeled SL of the tolerant rats were mainly Ig-positive cells.
J Immunol 1975 Sep
PMID:3H-uridine incorporation by small lymphocytes of tolerant rats: relationship to T and B lymphocytes. 12 99

Immune complex glomerulonephritis was induced in three groups of mice by long-term immunization. Two antigens of similar molecular weight were used. The first group was immunized with ferritin (mol wt 480,000). In altered glomeruli deposits of immune complexes were seen in the subendothelial and subepithelial spaces of the glomerular basement membrane (GBM) and in the mesangium. The immune complex deposits were formed by amorphous matrix with marked dense molecules of ferritin. The second group was immunized with human fibrinogen (mol wt 450,000). The immune complex deposits were present in the intramembranous, subepithelial and subendothelial spaces of the GBM and in the mesangium. These deposits were relatively less electron-dense and had a fine granular structure. The third group of mice were immunized with both ferritin and fibrinogen simultaneously. Two types of deposits situated subendothelially in the GBM and in the mesangium were seen in one animal of this group. One type of deposit resembled structurally the ferritin-antiferritin complex deposits, the other resembled the fibrinogen-antifibrinogen complex deposits. The individual deposits in the GBM and in the mesangium formed discrete homogeneous masses. The two types of deposit were occassionally in direct contact with one another, but were more often completely separate and were never mixed. It can be assumed that in at least some phase of the experiment both types of complex were present in the circulating blood simultaneously. However, since none of the complexes deposited in the GBM or in the mesangium were mixed, it seems probable that each type of complex is deposited separately in the form of "clusters" composed of a single type of complex. The phagocytic activity of mesangial cells of animals with complex glomerulonephritis was not increased when compared with control animals.
Virchows Arch B Cell Pathol 1977 Sep 15
PMID:Experimental immune complex glomerulonephritis in the mouse with two types of immune complexes. 14 86

The method for preparing a stable, biologically active, covalently linked ferritin--insulin complex has been modified to provide a 25-fold increase in yield compared to the original procedure while reducing the molar fatio of ferritin to insulin to 1:1 from 40:1. Ultrastructural studies of isolated adipocytes revealed specific binding of ferritin--insulin to the cell surface in irregular clusters associated with the glycocalyx coating. The number of ferritin--insulin molecules observed was consistent with the number of sulin molecules observed was consistent with the number of receptors calculated from 125I-labeled insulin binding studies. The ferritin--insulin was not observed in the cytoplasm of the cell but was found on the convave side of surface connected vesicles. These surface connected vesicles were part of an alveolar-like system of plasma membrane invaginations which project in various directions in the cytoplasm and by thin sectioning can appear as pinocytotic-like microvesicles. The morphological observations on ferritin--insulin binding were supported by the finding that 125I-labeled insulin binding was almost exclusively localized to highly purified plasma membranes isolated by fractionation of adipocytes after incubation with 125I-labeled insulin. These data supported the theory that insulin did not need to enter a cell to cause biological effects and was consistent with the negative cooperativity concept of insulin binding to cell receptors.
Proc Natl Acad Sci U S A 1975 Sep
PMID:Ultrastructural localization of insulin receptors on adipocytes. 17 64

A23187 and certain other carboxylate ionophores are capable of transferring Fe(II) but not Fe(III) across phospholipid bilayers (liposomes) and red cell membranes. A23187 is able to transfer Fe(II) from ferritin loaded liposomes when allied with a suitable redox couple and sink. The affinity of A23187 for Fe(II) is approximately five orders of magnitude greater than for Ca2+, as judged by two phase extraction techniques.
Biochim Biophys Acta 1977 Sep 19
PMID:Mobile carrier ionophores for Fe(II). 33 29


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