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L Valente

Publications and source records attributed to L Valente.

At least 37 records · Page 2Linked to original sources
PubMed1989

Thymopentin induces release of ACTH-like immunoreactivity by human lymphocytes.

Peripheral mononuclear (PMN) cells are known to produce ACTH-like immunoreactivity (ACTH-LIR) in vitro. Based on these findings the aim of this study was to find out whether thymopentin (the active pentapeptide of the native hormone thymopoietin) may stimulate ACTH-LIR production and release by cultured normal human lymphocytes. Thymopentin at concentration of 1 microgram/ml was capable of inducing ACTH-LIR release by normal human PMN cells (median 22 pg/ml) whereas ACTH-LIR inside cells was lower (median 11 pg/10(7) cells). The chromatographic characterization of the eluted material identified the presence of ACTH immunoreactive peptides with the elution characteristics of the precursors 31 K proopiomelanocortin, 22 K ACTH and 4.5 K ACTH, together with higher molecular weight material (greater than 43 K). These data demonstrate that thymopentin induces ACTH-LIR release by human lymphocytes, thus adding a novel factor to those already reported (corticotrophin releasing factor, lipopolysaccharide, viruses) capable of such function.

Adrenocorticotropic Hormone↗
PubMed1988

Inhibition of protein non-enzymic glycation induced by Bendazac.

Enhanced non-enzymic glycation of proteins has been suggested to play a role in the pathogenesis of diabetic microangiopathy. Thus pharmacological inhibition of this reaction could be envisaged to delay the development of late diabetic complications. In the present study we have investigated the effect of a new compound, 1-Benzylindazole-3-oxyacetic acid, Bendazac (BDZ) on the in vitro glycation of soluble proteins (albumin and fibrinogen) and isolated glomerular basement membrane (GBM). The data obtained indicate that BDZ is capable of reducing significantly the glycation of albumin and fibrinogen (p less than 0.001). When present in concentrations usually found in patients undergoing therapy (40-80 micrograms/ml), an inhibitory effect on soluble proteins was also observed. Inhibition of glycation of GBM was found only in the presence of the active metabolite (5 hydroxy BDZ) and at high glucose concentrations. These results suggest that BDZ could interfere with protein non-enzymic glycation and its use in patients with diabetes may be then taken into consideration to evaluate the effect on late diabetic complications.

Animals↗
PubMed1987

Auranofin increases the affinity of phorbol dibutyrate receptors in chronic lymphocytic leukemia cells (B cells).

Previous studies have shown that auranofin (AF), a lipophilic gold I complex, modulates metabolic events in leukocytes stimulated by phorbol esters, whose major cellular binding site is now known to be the Ca++/phospholipid-dependent protein kinase (protein kinase C). In these experiments we have investigated the effect of AF on the binding of phorbol dibutyrate (PDBu) to human chronic lymphocytic leukemia (CLL) B cells. AF enhanced binding of PDBu to its receptor in CLL cells by a) causing an increase in the affinity of PDBu receptors from Kd 20.3 nM to 7.3 nM, and b) enhancing translocation of PDBu receptors to the cell membrane. The increase in PDBu binding induced by AF in whole cells was only partially reversible by EGTA or the intracellular Ca++ antagonist TMB-8. Studies performed with quin-2-labeled cells showed that 100 microM AF caused a mean (+/- SD) rise in cytosolic Ca++ levels from 0.41 (0.12) to 0.85 (0.33) (n = 5). Thus the mechanism by which AF increases binding of PDBu to its receptor appears to be partially dependent on Ca++. These effects of AF occurred at cellular levels achieved in mononuclear cells during chrysotherapy of patients with rheumatoid arthritis.

Auranofin↗
PubMed1987

Calcium ionophore A23187 enhances human neutrophil superoxide release, stimulated by phorbol dibutyrate, by converting phorbol ester receptors from a low- to high-affinity state.

The calcium ionophore A23187 acted synergistically with phorbol dibutyrate (PDBu) to stimulate human neutrophil superoxide production. A23187 shortened the lag period and markedly increased the initial rate of neutrophil superoxide production induced by suboptimal concentrations of PDBu. 1 microM A23187 reduced the EC50 value for superoxide release from 56 to 8 nM PDBu. This effect of A23187 was correlated with enhanced binding of [3H]PDBu to its receptor and a reduction in the dissociation constant (Kd) from 27 to 10 nM, without altering the apparent total number of phorbol dibutyrate receptors. These actions of A23187 were abolished in the presence of EGTA or TMB-8, confirming a dependence on Ca2+.

Caenorhabditis elegans Proteins↗
PubMed1986

Calcium ionophore A23187 primes human B-cells for activation by phorbol dibutyrate by converting receptors for phorbol dibutyrate from a low to high affinity state.

The calcium ionophore A23187 synergised with phorbol dibutyrate-induced activation of human chronic lymphatic leukaemia B-cells, as assessed by modulation of the membrane receptor for mouse erythrocytes. Thus A23187 (1 microM), which alone had no effect on expression of the receptor for mouse erythrocytes, reduced the EC50 and shortened the lag period for modulation of this receptor by phorbol dibutyrate. This action of A23187 was shown to be due to enhanced binding of [3H]phorbol dibutyrate to its receptor (phospholipid/Ca++ dependent protein kinase C) whose affinity was altered from a predominantly low affinity state (Kd 83 nM) to high affinity (Kd 9 nM). A23187 had no effect on the total number of phorbol dibutyrate receptors. EDTA abolished these actions of A23187.

B-Lymphocytes↗
PubMed1984

A subclass of albumin recognized by inhibition of phosphatidylethanolamine-mediated agglutination of mouse erythrocytes.

Agglutination of mouse erythrocytes by non-choline phospholipids is inhibited by a factor in mammalian sera. The inhibitor cochromatographed with albumin on dye-agarose conjugates, was retained by an anti-albumin affinity column, was neutralized by anti-albumin antibody and found in a serum fraction in which only albumin could be detected. A variety of commercial preparations of albumin (fraction V, crystalline) did not inhibit. However, they acquired potent inhibitory activity when treated with low molecular weight thiols. The inhibitory activity of serum was increased 8-fold by treatment with dithiothreitol. Other proteins were not activated in this way. Inhibitory activity increased with average free sulphydryl content of treated albumin, up to six thiol groups per molecule. Alkylation of these sulphydryl groups did not diminish inhibitory activity. Thiols also induced polymerization of albumin. Inhibitory albumin in serum was largely monomeric. We propose that the inhibitor is a type of serum albumin which is lost or inactivated during preparation of commercial albumin, and which shares a structural feature, necessary for inhibition, with thiol-reduced albumin and the ligand on mouse erythrocytes.

Adult↗
PubMed1984

A phosphatidylethanolamine-containing complex on human B cells that mediates rosette formation with mouse erythrocytes.

The maturation-associated human B cell rosette receptor (MER) for mouse erythrocytes has been solubilized from B cells by mild trypsinization. It specifically agglutinates mouse red cells. Material with hemagglutinating activity partitioned into the lipid-soluble phase of a Folch partition of the trypsin extract was sensitive to phospholipase C and alkali, and on two-dimensional thin layer chromatography, it co-migrated principally with phosphatidylethanolamine (PE). Phosphatidylcholine, the major lipid present, was inactive. The relationship of phospholipid structure to hemagglutinating activity has been described. PE in the crude trypsin extract was associated with unidentified glycoprotein and albumin. Material containing hemagglutinating lipid bound to a wheat germ lectin-Sepharose column and was released by N-acetylglucosamine, indicating that the PE was complexed with glycoprotein. When the crude trypsin extract or eluate from the lectin column was extracted with aqueous phenol, hemagglutinin in the aqueous phase no longer bound to wheat germ lectin-Sepharose; however, albumin was greatly enriched, indicating that some of the PE exists in a complex with albumin. The molar ratio of PE to albumin was approximately 200:1. After delipidation, this albumin (in molar excess) inhibited hemagglutination by PE in the same way as a recently described subclass of serum albumin. Studies with phospholipase-treated B cells were also consistent with PE being the MER. We conclude that MER is PE, existing in a complex containing glycoprotein and a subclass of albumin. The capacity to form rosettes can be transferred to nonrosetting Raji B cells by the complex, but not pure PE, indicating that the proteins may be involved in orienting PE correctly for it to function as the MER.

Animals↗
PubMed1984

Mechanism of induction of mouse erythrocyte receptor switch in human B cells.

An early event in phorbol ester-induced maturation of chronic lymphocytic leukemic (CLL) B cells is a membrane change characterized by the inactivation of a mouse erythrocyte receptor (MER). This event, the MER-switch, is quantified by inhibition of rosette formation. By using [3H]phorbol dibutyrate ([3H]PDBu), both to stimulate MER-switch and assay binding of PDBu to CLL cells, it was shown that MER-switch was an irreversible, time-dependent event which occurred some time after maximal binding of [3H]PDBu to cells. Two classes of binding sites, one of high affinity (Kd 1 to 2 nM) at low frequency (1.5 to 5 X 10(4) sites per cell), and a lower affinity site (Kd 33 to 50 nM) of higher frequency (2 to 3.5 X 10(5) sites per cell), were detected. Binding of [3H]PDBu was inhibited by phorbol ester analogs that stimulated MER-switch, but not by inactive analogs. This, and the similarity in shapes of the binding and rosette inhibition curves over a range of concentrations, suggests that stimulation of MER-switch by phorbol esters is due to this specific binding. The phorbol ester receptor and MER are distinct because MER-ve T cells and MER-ve atypical B cells from a patient with CLL had both classes of PDBu receptor. Solubilized MER did not bind [3H]PDBu. Time-course studies, and the irreversibility of the switch, despite removal of most of the bound [3H]PDBu, indicate that inhibition of rosetting is not due to competitive or steric hindrance by phorbol esters. Equivalent activities of soluble MER were released from fresh and phorbol ester-treated CLL cells, indicating a rearrangement of MER, rather than a loss. A supernatant of phytohemagglutinin-stimulated human spleen cells also induced MER-switch in CLL lymphocytes, suggesting that a lymphokine may be a natural inducer of this event.

Animals↗
PubMed1983

Agglutination of mouse erythrocytes by binding of non-choline phospholipids to a 70 000-Dalton protein.

The structure of some phospholipids that cause agglutination of mouse erythrocytes has been studied. Haemagglutination is a property of non-choline-containing phospholipids; the phosphate group is essential and unsaturated fatty acids optimal. A protein of Mr 70 000 was isolated from mouse erythrocyte membranes which completely inhibited phospholipid-mediated erythrocyte agglutination. It is proposed that this protein is the phospholipid binding site on mouse erythrocytes and the ligand for the human B-lymphocyte receptor for mouse erythrocytes. Preliminary investigations suggest that a similar inhibitor of phospholipid-mediated agglutination is found in serum. Agglutination of mouse erythrocytes by phospholipid and specific inhibition by the 70 kDa membrane protein constitute a simple system for studying the interaction of phospholipid with protein.

Animals↗
PubMed1982

Human B-lymphocyte maturation sequence revealed by TPA-induced differentiation of leukaemic cells.

Normal human B cells and leukaemic B-cell populations in common-type CLL undergo sequential shifts in proportions of the three B-cell subsets, defined by expression of mouse erythrocyte receptors R1 and R2, during TPA-induced differentiation to plasmacytoid cells in vitro, suggesting that the B-cell differentiation pathway is R1 +R2+ leads to R1 -R2+ leads to R1 -R2- leads to immature plasmacyte. Maturation of the less common type of CLL with a predominance of R1 -R2+ type cell was in agreement with this model. Changes in Fc gamma, Fc mu and C' receptors were also observed during maturation. A model of human B-cell maturation is presented on which common sites of blockage in leukaemia can be located.

B-Lymphocytes↗
PubMed1982

Two maturation-associated mouse erythrocyte receptors of human B cells. I. Identification of four human B-cell subsets.

Using rosetting tests with untreated mouse erythrocytes (M) and pronase-treated M (pro M), four human B cell subsets can be identified. Three of these, possessing the phenotypes BM+ pro M+, BM- pro M+ or BM- pro M-, constitute 17%, 61% and 22% of normal blood B cells respectively. The fourth subset, BM+ pro M-, does not occur in normal tissues but was found in the pre-B-cell line of Raji cells, indicating that this phenotype may be a marker for early B cells. Some differences in the proportion of each subset were found in cord blood, lymph nodes and tonsils. Surface-immunoglobulin-positive (SIg+) and -negative (SIg-) non-T cells were present in each subset. M and pro-M rosetting tests were applied to cells from blood of 27 cases of chronic lymphocytic leukaemia (CLL) and to cells from involved nodes, spleen or marrow in five cases of non-Hodgkin's lymphoma (NHL). In 15 cases of CLL, there was considerable increase in the BM+ pro M+ subset (BM+ pro M+ type CLL); in seven cases, there was a predominance of BM- pro M+ cells and in another four cases, BM- pro M- cells predominated. All five cases of NHL were greatly enriched in BM- pro M- cells. There was no obvious correlation between rosetting and other surface markers but BM- pro M- clones in CLL or NHL always stained brightly with FITC-anti-Ig. This was not found in BM+ pro M+ or BM- pro M+ clones. Rosette formation of neuraminidase-treated B cells with M identifies the same subset as B-pro-M rosetting in normals and CLL. Evidence is presented that two types of receptors are involved in M and pro-M rosetting, designated R1 and R2, binding to corresponding M ligands L1 and L2. M rosetting is due to R1-L1 binding while R2-L2 binding mediates B-pro-M rosetting. Shifts between subsets within the same clone in some cases of CLL suggest that the subsets are distinct maturational stage of B-cell development rather than families of B cells of different lineage. The following B-cell maturation sequence is proposed: R1+ R2- lead to R1+ R2+ leads to R1- R2+ leads to R1- R2-.

Adult↗
PubMed1982

Two maturation-associated mouse erythrocyte receptors of human B cells. II. Isolation and partial characterization of a B-cell lectin with specificity of R1.

Trypsin treatment of chronic lymphocytic leukaemia (CLL) cells which have the capacity to rosette with mouse erythrocytes (M), the BM+ subtype, inhibits their capacity to rosette and releases a substance into the supernatant which agglutinates mouse and rat erythrocytes but not erythrocytes of five other species tested. This substance has been named immature B-cell lectin (IBL). The specificity of IBL was further demonstrated by fluorescence labelling, absorption and latex rosetting. IBL does not bind to pronase-treated M (pro M), indicating that it has the specificity of R1 as distinct from R2 which binds to a pronase-resistant ligand on M. Other evidence that IBL is associated with B-cell membrane receptors for mouse erythrocytes is as follows: (1) The amount of IBL released into the supernatant correlated with the trypsin sensitivity of M rosetting with different clones of BM+ CLL cells. (2) Only small amounts of IBL were released from non-rosetting cells (T cells and mature B cells). (3) Binding properties of IBL were inhibited by extract of M but not extract from ox erythrocytes. (4) High-titre solutions of IBL conferred the capacity to form M rosettes on certain types of non-rosetting B cells. IBL has a dual binding specificity. Its binding to M is inhibited by fetuin and mannan, while its binding to B cells is not inhibited by these substances. The relationship of IBL to other membrane lectins including fibronectin is discussed. Preliminary characterization indicates a high-molecular-weight (at least 300,000 daltons) glycoprotein which has a pronounced tendency to aggregate in solution. The relationship of IBL to stages of human B-cell maturation is discussed.

Animals↗
PubMed1981

Loss of receptor activity for mouse erythrocytes precedes tumour promoter-induced maturation of chronic lymphocytic leukaemia cells.

The tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induced differentiation in lymphocytes from patients with chronic lymphocytic leukaemia (CLL). The differentiation was detected by the appearance of cytoplasmic immunoglobulin (CIg) and a plasmacytoid morphology, and was accompanied by the loss of the ability of the CLL cells to rosette with mouse erythrocytes (M). Loss of M rosetting occurred rapidly (within 10 min), was not prevented by cycloheximide or actinomycin D and was elicited by low concentrations of TPA (ED50 8 X 10(-10) M). Inhibition of rosette formation was induced by other phorbol diester promoters, but not non-promoting derivatives. Loss of the capacity to form M rosettes occurs before events which are evidently related to genome activation.

Animals↗
PubMed1981

B lymphocyte specificity of lectins of Cepaea nemoralis and Dolichos biflorus: paradoxical binding of anti-A active lectins to human lymphocyte subclasses.

Binding of four blood group A-specific lectins, from Helix pomatia (HP), lucorum (HL), Cepaea nemoralis (CN) and Dolichos biflorus (DB) to human lymphocytes was determined. Use was made of lectins attached to latex particles, as convenient probes to detect binding of lectins to individual cells, Specificity of lectin-latex probes was demonstrated by comparison with agglutination and fluorescent lectin binding; experiments with untreated and enzyme-treated human and animal erythrocytes confirmed the specificity of the lectin-latex beads as did inhibition in the presence of N-acetyl-galactosamine, the immunodominant sugar of blood group A substance. The binding of HP to T cells and a proportion of B, and non-B, non-T cells is confirmed. Binding to B cells in chronic lymphocytic leukaemia (CLL) is also confirmed. HP-latex had the same specificity as soluble HP, but binding did not require pretreatment of lymphocytes with neuraminidase. HL-latex had the same specificity for erythrocytes, normal lymphocyte subpopulations and CLL lymphocytes as HP, but the binding was weaker and required pretreatment of the lymphocytes with neuraminidase to demonstrate it. Contrary to expectation, CN and DB bound to B lymphocytes and did not bind to T lymphocytes. CN binding was almost completely restricted to B cells, whereas DB bound to part of the non-B, non-T populations as well as to a substantial proportion of B cells. Neither CN nor DB labelled malignant T cells. Both CN and DB bound to B cells in CLL. As with HP, pretreatment of lymphocytes with neuraminidase increased the accessibility of receptors, but was not essential to demonstrate labelling with CN-, and DB-latex preparations. Binding of each lectin to lymphocytes was independent of ABO blood group of donor suggesting that ABO antigens may be expressed poorly, if at all, on lymphocytes. Binding is probably due to additional specificities possessed by these lectins. Protease treatment destroyed CN- and DB-binding sites but not HP receptors suggesting that at least two types of binding site are involved.

ABO Blood-Group System↗