PubMed Health⌕ Search

Biomedical subjects

M Fresno

Publications and source records attributed to M Fresno.

At least 127 records · Page 7Linked to original sources
PubMed1985

Specific effect of anti-transferrin antibodies on natural killer cells directed against tumor cells. Evidence for the transferrin receptor being one of the target structures recognized by NK cells.

Treatment of PBL or Percoll-isolated LGL with anti-transferrin antibodies plus complement reduced their natural killing activity against K-562 cells between 30 and 70%. The same antibodies inhibited natural cytotoxicity when added directly to the assay. Similar depletion or inhibition of NK cytotoxicity was observed when using HeLa cells as targets. The decrease or inhibition by transferrin antibodies was less marked when IFN-treated PBL or LGL as effector cells were used. The inhibition of anti-transferrin antibodies seems to be located at the level of the effector cell population. When PBL but not target K-562 cells were pretreated with anti-transferrin antibodies and were washed before use in the assay, cytotoxicity was decreased by 50%. In addition, about 80% of the LGL positively selected on anti-transferrin plates stained with Leu-11. Furthermore, no reduction by anti-transferrin antibodies plus complement treatment of PBL or LGL, or inhibition by antibodies alone, was observed when the cells were tested against HSV-1-infected cells. Membrane extracts from LGL inhibited NK cytotoxicity against K-562 or HeLa cells. Moreover, the inhibitory component of this extract was removed by anti-transferrin IgG but not by control IgG. These results are in agreement with the recent hypothesis that NK cells recognize the transferrin receptor in tumor target cells, because both the transferrin receptor and anti-transferrin antibodies may share a similar structure that interacts with the NK cells.

Adult↗
PubMed1983

Affinity-purified antigen-specific products produced by T cells share epitopes recognized by heterologous antisera raised against several different antigen-specific products from T cells.

Heterologous antisera to murine or rat T-cell antigen-binding molecules (T-ABM) were raised in rabbits or sheep. The T-ABM used for immunization were purified by affinity for antigen and did not bear known immunoglobulin isotypes. T-ABM and anti-T-ABM were raised in three separate laboratories. Antisera to T-ABM were exchanged and tested for binding to T-ABM in three separate laboratories. Thus antisera to at least three distinct T-ABM were tested directly for binding to T-ABM or by adsorption of biological activity. Rabbit antisera to murine trinitrophenol (TNP)-specific T-ABM or rat AgB-specific T-ABM bound both murine or rat T-ABM, indicating evolutionary conservation of T-ABM. Similar results were found with sheep antisera to murine T-ABM. In addition, all heterologous anti-T-ABM antisera used bound murine T-ABM specific for TNP, 4-hydroxy-3-nitrophenyl acetate (NP), SRBC, or T-cell membrane proteins with similar structure. Thus, there is a commonality of antigenic determinants between various T-ABM and T-cell membrane homologues which may be T-cell surface receptors for foreign antigen.

Animals↗
PubMed1983

Enhancement of susceptibility of HSV-1-infected cells to natural killer lysis by interferon.

The effect of interferon (IFN) on the natural killer (NK) activity of human PBL against HSV-1-infected HeLa cells was studied. Human PBL from several individuals did not consistently show a preferential lysis of HSV-1-, vaccinia-, or adenovirus type 5-infected cells with respect to uninfected HeLa cells. Treatment with IFN of effector PBL increased their lytic activity but did not alter the degree of preference on the lysis of the target cells shown by untreated PBL. Pretreatment with IFN of HSV-1-infected HeLa cells increased their susceptibility to lysis 5- to 10-fold. In contrast, identical pretreatment of the uninfected, adenovirus type 5- or vaccinia virus-infected HeLa cells before the assay decreased their susceptibility to NK lysis. This effect was not likely to be due to a block of the viral replication because other inhibitors like mitomycin C did not have the same effect. All target cells induced IFN synthesis in effector PBL cells. A similar level of IFN was induced by HSV-1-infected or uninfected HeLa cells. Pretreatment with IFN of HSV-1-infected, but not uninfected, HeLa cells induced 5 to 10 times more IFN by PBL, in good correlation with the increase in lytic activity. PBL treated with IFN, however, in conditions to give maximal stimulation of NK activity, presented the same preferential lysis of HSV-1-infected HeLa cells and synthesized similar levels of IFN as untreated PBL. In addition, HSV-1-infected HeLa cells were killed through different target structures than uninfected cells. Taken together, our results indicate an effect of IFN at the level of the NK target structures in HSV-1-infected HeLa cells by increasing either their number or, more likely, their affinity for NK cells independent of the effect of IFN in the effector cells or as an antiviral agent.

Cytotoxicity, Immunologic↗
PubMed1982

Antigen-specific T lymphocyte clones. III. Papain splits purified T suppressor molecules into two functional domains.

Purified molecules (70,000 mol wt) from a T-suppressor (Ts) clone bind to sheep erythrocyte glycophorin and specifically suppress the response to this antigen. Papain splits purified 70,000-mol wt Ts molecules into two peptides: mol wt 45,000 and 24,000. The 45,000-mol wt peptide nonspecifically suppresses antibody response to several antigens and lacks antigen-binding activity. The 24,000-mol wt peptide does not suppress but retains antigen-binding activity. The results indicate that papain splits the Ts molecule into a "constant" region responsible for function and a "variable" region responsible for antigen-binding. Since binding of the 70,000-mol wt molecule to antigen also results in release of the 45,000 mol wt subunit, this cleavage may allow Ts molecules specific for one determinant to suppress immunity to complex foreign proteins.

Animals↗
PubMed1982

Proteins synthesized by inducer T cells: evidence for a mitogenic peptide shared by inducer molecules that stimulate different cell types.

Inducer T lymphocytes synthesize and secrete peptides that stimulate growth and differentiation of many cell types, including lymphocytes and monocytes that kill foreign organisms, B lymphocytes, mast cells and hematopoietic precursor cells. To define these inducer molecules more precisely, we have generated clones of these T cells as a source of homogeneous material for biochemical analysis. These clones synthesize peptides that stimulate T and B cells to divide and that also induce the latter cells to secrete immunoglobulin. Inducer cells synthesize a 14 kilodalton growth polypeptide that stimulates T and B lymphocytes, as well as other cell types, to divide. This 14 kilodalton peptide is normally associated with different, larger peptides that appear to focus its mitogenic activity to one or another target cell.

Animals↗
PubMed1981

Antigen-specific T lymphocyte clones. I. Characterization of a T lymphocyte clone expressing antigen-specific suppressive activity.

We have generated continuously propagatable T lymphocyte clones to study antigen-specific T cell functions. All Ly-2+ clones mediate suppressive activity and secrete a characteristic pattern of polypeptides that differs from Ly-2- T cell clones. Cells of one clone, Cl.Ly23/4, specifically bind glycophorin from sheep erythrocytes (SRBC). After incubation with [35S]methionine, supernate material from this clone also contains biosynthetically labeled 70,000-mol wt proteins that specifically bind to SRBC and this binding is inhibited by glycophorin from sheep but not other erythrocytes. These antigen-binding 70,000-mol wt peptides specifically and completely suppress primary anti-SRBC responses generated by mixtures of primed Ly-1+2- cells and B cells. Suppression by these antigen-binding peptides reflects direct inhibition of T-helper activity.

Animals↗
PubMed1981

Antigen-specific T lymphocyte clones. II. Purification and biological characterization of an antigen-specific suppressive protein synthesized by cloned T cells.

We have generated an antigen-specific T suppressor clone that synthesizes 70,000-mol wt peptides that have antigen-specific-binding activity. Although these data also indicated that antigen-binding peptides completely inhibited the in vitro primary response to a complex antigen, suppression might reflect the combined biologic activities of many different 70-mol wt polypeptides or polypeptides associated with the 70,000-mol wt material by noncovalent interactions. The protein responsible for antigen-specific suppression was therefore purified to virtual homogeneity after sequential separation of internally labeled supernate peptides on Sephacryl S-200 and DEAE-cellulose columns followed by isoeleetrofocusing. The resulting protein is greater than 95 percent homogeneous according to sodium dodeeyl sulfate-polyacrylamide electrophoresis and represents two peptides having two very close but distinguishable isoelectric point values of approximately 5.0. The purified molecules are retained by columns coated with lentil lectin or antigen but not by columns coated with antisera specific for immunoglobulins, the I region of the major histocompatibility complex or Ly-1 or Ly-2 antigens. Less than 50 pg of the purified glycoprotein specifically and completely suppresses production of anti-sheep erythrocyte plaque-forming cell by mixtures of 10(6) Ly-1 cells and B cells and this is a result of inactivation of Ly-l-mediated helper function. Specific inactivation of T (Th) cells by the 70,000-mol wt molecule is rapid, specific, and requires the presence of antigen. The mechanism of specific suppression of Th function may depend upon two functionally distinct regions of the 70,000-mol wt molecule: one that binds antigen and a second that mediates suppression.

Animals↗
PubMed1981

Use of cloned populations of mouse lymphocytes to analyze cellular differentiation.

We describe a method for generation of homogeneous cell populations that each arise from clonal expansion of cells at a discrete stage of differentiation within a single lineage. We have used this to produce continuously propagatable lymphocyte clones. Each clone represents a cell at a progressive stage of thymus-dependent cellular differentiation. These cloned cells bear stable surface membrane glycoproteins characteristic of precursor cells and mature progeny; conditions allowing maximal cloning efficiencies for each cell type (10-85%) have been established. Mature lymphocyte clones continue to express specialized function and provide material for biochemical analysis of T lymphocyte functions; one fully differentiated clone from the "inducer" lymphocyte set synthesizes a molecule that activates other lymphocytes to secrete immunoglobulin. This activity is associated with a highly purified molecule having a molecular weight of 45,000 daltons and an isoelectric point of approximately 6.0. This molecule, together with clones of precursor and mature T lymphocytes, may provide a system to further study the mechanisms of gene activation during cellular differentiation.

Antigens, Surface↗
PubMed1980

Inhibitory effects of 'cap' analogues on globin mRNA and encephalomyocarditis RNA translation in a reticulocyte cell-free system.

The cap analogues 7-methylguanosine 5'-phosphate [m7G(5')p], 7-methylguanosine 5'-triphosphate [m7G(5')ppp] and 2'-O-methylguanosine 5'-triphosphate [Gm(5')ppp] inhibit the translation of capped globin mRNA and encephalomyocarditis (EMC) RNA (a naturally uncapped mRNA) in a reticulocyte cell-free system. This inhibition occurs at the level of protein synthesis initiation and is of a competitive type since it can be overcome by increasing the mRNA concentration. However, the translation of globin mRNA is more sensitive to the inhibitory effects of the cap analogues m7G(5')p and m7G(5')ppp than translation of EMC RNA. The same spectra of specific inhibition is also observed with some other initiation inhibitors such as aurintricarboxylic acid, which inhibits mRNA binding, but not with pactamycin which does not affect mRNA interaction. A model is presented suggesting that this preferential inhibition by cap analogues could be explained mainly by the different affinities of globin mRNA and EMC RNA for the initiation complexes between 40-S subunits and Met-tRNAf. Moreover Gm(5')ppp cannot be considered simply as a cap analogue since it also affects some step prior to mRNA binding.

Animals↗
PubMed1977

Inhibition of translation in eukaryotic systems by harringtonine.

The Cephalotaxus alkaloids harringtonine, homoharringtonine and isoharringtonine inhibit protein synthesis in eukaryotic cells. The alkaloids do not inhibit, in model systems, any of the steps of the initiation process but block poly(U)-directed polyphenylalanine synthesis as well as peptide bond formation in the fragment reaction assay, the sparsomycin-induced binding of (C)U-A-C-C-A-[3H]Leu-Ac, and the enzymic and the non-enzymic binding of Phe-tRNA to ribosomes. These results suggest that the Cephalotaxus alkaloids inhibit the elongation phase of translation by preventing substrate binding to the acceptor site on the 60-S ribosome subunit and therefore block aminoacyl-tRNA binding and peptide bond formation. However, the Cephalotaxus alkaloids do not inhibit polypeptide synthesis and peptidyl[3H]puromycin formation in polysomes. Furthermore, these alkaloids strongly inhibit [14C]trichlodermin binding to free ribosomes but hardly affect the interaction of the antibiotic with yeast polysomot interact with polysomes and therefore only inhibit cycles of elongation. This explains the polysome run off that has been observed by some workers in the presence of harringtonine.

Alkaloids↗
PubMed1976

Initiation of the polypeptide chain by reticulocyte cell-free systems. Survey of different inhibitors of translation.

In order to elucidate the mechanism of action of inhibitors that block the initiation of protein synthesis in mammalian systems, we have studied the following steps: (a) formation of the ternary complex Met-tRNAr-IF-E2-GTP, (b) binding of the initiator Met-tRNAf to the 40-S ribosomal subunit in the presence of initiation factors and dependent or not on the addition of mRNA, (c) formation of the initiation complex with 80-S ribosomes and (d) formation of the first peptide bond. Adrenochrome, aurintricarboxylic acid, polydextran sulphate, pyrochatechol violet and showdomycin block the formation of the ternary complex Met-tRNAf-IF-E2-GTP. Edeine A1, aurintricarboxylic acid and polydextran sulphate block the binding of the mRNA to the 40-S ribosomal subunit. Pactamycin induces the formation of stable smaller initiation complexes which are unable to go through the subsequent steps of initiation. Stimulation of the binding of the initiator Met-tRNAf to the 80-S ribosome in the presence of initiation factors is observed with sparsomycin and antibiotics of the sesquiterpene family (verrucarin A, trichodermin and trichothecin). However, these antibiotics block the reaction of the bound Met-tRNAf with puromycin. Narciclasine has no effect on the binding of the initiator to the ribosome but strongly blocks its reaction with puromycin. We have developed a simple technique to detect the Met-tRNAf-40-S-subunit-poly(A, G, U) initiation complexes by chromatography on Sepharose 6B columns. The requirements for the formation of such complexes measured by this technique and its comparison with the sucrose gradient centrifugation method are described.

Animals↗
PubMed1975

Inhibitors of polypeptide elongation on yeast polysomes.

Yeast polysomes are very active for amino acid incorporation when supplemented with elongation factors and the different components required for elongation of the polypeptide chain. This polysomal system is suitable for the study of the individual streps of the elongation cycle and to test the effect of different inhibitors. Anisomycin, trichodermin, trichodermol, trichothecin, fusarenon X, sparsomycin and blasticidin S inhibit peptide bond formation on these polysomes, whereas diphtheria toxin, pederine, cycloheximide and cryptopleurine block translocation.

Amino Acids↗