Biomedical subjects

M Mirshahi

Publications and source records attributed to M Mirshahi.

At least 73 records · Page 4Linked to original sources

PubMed1992

A common epitope on human tumor necrosis factor alpha and the autoantigen 'S-antigen/arrestin' induces TNF-alpha production.

A common epitope on S-antigen (arrestin), a potent autoantigen inducing experimental autoimmune uveoretinitis (EAU), and on human tumor necrosis factor alpha (hTNF alpha) was revealed using two monoclonal antibodies to S-antigen which inhibit EAU induction. The minimal common sequence for monoclonal antibody recognition is GVxLxD in the S-antigen/hTNF alpha amino acid sequences. Peptides containing this sequence motif exhibited monocyte activating capacity similar to the autocrine stimulatory capacity of hTNF alpha itself. In the S-antigen this activity was located from residue 40 to 50, corresponding to the peptide PVDGVVLVDPE (epitope S2). In hTNF alpha, the monocyte activating capacity correlated to residue 31 to 53, corresponding to the peptide RRANALLANGVELRDNQLVVPSE (peptide RRAN). The identified regions define common functional structures in the autoantigen and in the hTNF alpha molecule. The data suggest a regulatory function of this particular structure in TNF alpha expression and in autoimmunity.

Amino Acid Sequence↗

PubMed1992

Humoral immune response against the S-antigen/TNF alpha common epitope in rat EAU suppressed by the monoclonal antibody S2D2.

S-antigen (S-Ag)-induced experimental autoimmune uveoretinitis (EAU) in rats can be suppressed by injecting the mouse monoclonal antibody (mAb) S2D2 or a polyclonal rat anti-idiotype S2D2 (anti-Id S2D2) antibody, the internal image of the epitope of S-Ag recognized by mAb S2D2. This epitope located in amino acids 40-50 of bovine S-Ag (peptide S2), displays an homology with a sequence of human tumor necrosis factor alpha (hTNF alpha) (peptide RRAN) which is also recognized by S2D2. (Stiemer et al., this symposium). We show that one injection of S2D2 at the time of immunization with S-Ag suppressed EAU and modulated the production of antibodies against peptides of bovine or human S-Ag containing the S2 epitope and against peptide RRAN. Immunization against anti-Id S2D2 stimulated antibody production to peptide S2 and RRAN and inhibited EAU. These data suggest that disease suppression could be related to the production of antibodies against the S-Ag/TNF alpha common epitope.

Amino Acid Sequence↗

PubMed1992

Cytokine induction by immunomodulatory epitopes in S-antigen and tumor necrosis factor alpha.

Common epitopes on S-antigen (arrestin), a potent autoantigen inducing experimental autoimmune uveoretinitis (EAU), and on human tumor necrosis factor alpha (hTNF alpha) are revealed with monoclonal antibodies (mAb) to S-antigen, which inhibit EAU induction. The minimal common sequence for mAb recognition is GVxLxD in the S-antigen/hTNF alpha amino acid (aa) sequences. Peptides containing this sequence motif exhibit monocyte activating capacity analogous to the autocrine stimulatory capacity of hTNF alpha itself. In S-antigen this activity is located at epitope S2 (aa residues 40 to 50), corresponding to the peptide PVDGVVLVDPE (peptide S2). In hTNF alpha the monocyte activating capacity correlates to aa residue 31 to 53, corresponding to the peptide RRANALLANGVELRDNQLVVPSE (peptide RRAN). Peptide S2 but not peptide RRAN is competing for mAbs S6H8 and S2D2 binding to S-antigen. Anti-idiotypic antibodies to S2D2 compete with peptide S2 but not peptide RRAN for binding to mAbs S2D2 and S6H8. In human retinal S-antigen epitope S2 is localized at the aa residues 44-54 and is cleaved in the human peptide 4 (aa 31-50). Competition experiments with peptide 4 (aa 31-50) and peptide 5 (aa 41-60) indicate that the C-terminal aa residues VDPD in the epitope S2 play an important role for internal image recognition of the anti-idiotypic antibodies. Peptide S2 and peptide RRAN define common functional structures in the autoantigen and hTNF alpha molecules. The data suggest regulatory functions of the peptides in cytokine expression, network regulation and in autoimmunity.

Amino Acid Sequence↗

PubMed1991

Immunopurification of an S-antigen-like protein from human platelets.

S-antigen (also named arrestin or 48K protein) is a protein abundant in photoreceptor cells of vertebrates and invertebrates. The presently known function of this protein in retina is to arrest the enzymatic cascade of phototransduction in retinal rods, through its binding to photoactivated and phosphorylated rhodopsin. Proteins closely related to S-antigen were recently demonstrated in several non photosensitive cells. In this work, we demonstrated the presence of a protein similar to retinal S-antigen with regards to its immunoreactivity with a panel of monoclonal antibodies and its molecular weight in soluble extracts of human platelets. This protein was purified by immunoaffinity chromatography using a rabbit antibody to retinal S-antigen. This S-antigen-like protein could have a regulatory function in G-protein-mediated transduction of chemical signals in platelets, similar to arrestin function in phototransduction.

Antibodies, Monoclonal↗

PubMed1991

Detection of undegraded fibrin and tumor necrosis factor-alpha in venous leg ulcers.

The pathogenesis of venous leg ulcers is based on the leakage of fibrinogen leading to pericapillary fibrin cuff and plugging of capillaries by white blood cells. Eight patients with venous leg ulcers have been studied with a panel of antibodies reactive for fibrinogen, fibrin, fibrin degradation products, and various cell-associated markers for polymorphonuclear cells, monocytes, and B and T lymphocytes. Our results showed that pericapillary fibrin cuff was mainly composed of undegraded fibrin and that, in the granulation tissue, tumor necrosis factor-alpha and elastase activities were detectable in monocytes and polymorphonuclear cells, respectively. Only few activated lymphocytes were present. On the basis of these results, it is assumed that inflammation generated by activated white blood cells that accumulate under unrelieved pressure is the key event. Tumor necrosis factor-alpha synthesized by activated monocytes may therefore induce the formation of pericapillary fibrin cuffs. Pericapillary fibrin cuffs and toxic metabolites released by polymorphonuclear cells may explain the absence of wound repair.

Aged↗

PubMed1991

Distribution of arrestin-like protein and beta-subunit of GTP-binding proteins in quail choroid plexuses.

Monoclonal antibodies (Mabs) directed against retinal arrestin (S-antigen) were used to detect and characterize this protein in choroid plexus (CP) of quails maintained during eight days, either under long-day photoperiods or in constant darkness. Immunocytochemistry and Western blotting confirmed the presence and the distribution of an arrestin-like protein in quail CP. Arrestin-like immunoreactivities in CP were compared with those obtained with Mabs to beta 36-subunit of G proteins (G beta), alpha-subunit of transducin and rhodopsin. Rhodopsin-like and transducin-like proteins could not be detected in choroidal cells, whereas intense positive reactions were observed with anti-G beta and anti-arrestin Mabs. The strongest immunoreactivities were found in choroidal ependymocytes of the lateral and IIIrd ventricles. In CP epithelial cells lining the IVth ventricle, very weak or no immunoreactivity could be detected with Mabs to arrestin, while Mab against G beta subunit always provided a positive reaction. In quails maintained in constant darkness, arrestin- and G beta-immunoreactivities of CP epithelial cells displayed changes in cellular distribution and intensity (decrease or disappearance of the immunoreactions). The strong arrestin-like immunoreaction located in the apical region of ependymocytes suggests the preferential association of the protein with choroidal microvilli and a possible role in cerebrospinal fluid production assumed by CP cells.

Animals↗

PubMed1991

Immunological screening of a glycoprotein antigen expressed by Zajdela ascites hepatoma cells on normal rat tissues and tumour cells.

Expression of the glycoprotein MII2 antigen originally identified in Zajdela ascites hepatoma cells was investigated in several normal rat tissues and in more or less differentiated tumours using biochemical and immunological approaches. SDS-polyacrylamide gel electrophoresis followed by fluorography or immunoblotting with an antiserum raised against the purified MII2 antigen revealed that this antigen was absent from normal liver cells. ELISA assays, indirect immunofluorescence and immunoprecipitation experiments using the same antiserum showed that this glycoprotein was not expressed in various normal tissues such as liver, spleen, lung, pancreas, intestine and stomach, but it was unexpectedly detected in kidney and thymic tissues. However, the molecular weight of the antigens immunoprecipitated from kidney and thymus was lower than the one of MII2 (Mr of 60,000 versus 110,000-160,000 for purified MII2). No staining was observed in embryonic rat liver at 10 and 20 days of development. Moreover, this antigen was present on the surface of Morris hepatoma 7777, another rapidly proliferating and poorly differentiated hepatocellular carcinoma. In contrast, this antigen was not detected on the surface of in vitro Zajdela hepatoma cells (ZHC) or of partially differentiated hepatomas (Faza) which have recovered some hepatic functions. In addition, the MII2 antigen was found on the human non-hepatic HT-29 tumour cell line, under its undifferentiated form (HT-29 G+ subline). The possible relationships between the expression of this antigen and both the malignant transformation process and the differentiation process are discussed.

Animals↗

PubMed1991

Early disappearance of alpha-transducin in light-induced photoreceptor degeneration in albino rats.

Progressive degeneration of retinal photoreceptor cells occurs in albino rats when exposed to continuous lighting. Three proteins involved in the phototransduction cascade were immunodetected in these cells after various durations of continuous illumination. We found that S-antigen (arrestin) and rhodopsin immunoreactivities persisted for 1-2 months during the degenerative process, whilst immunoreactivity of the alpha subunit of transducin totally disappeared between day 2 and day 4 of continuous light exposure. This suggests that continuous illumination could impair alpha-transducin synthesis, a possible causal factor of photoreceptor damage.

Animals↗

PubMed1991

[Presence of arrestin (S-antigen)-like proteins in vegetable cells].

Arrestin (or S-antigen) is a protein that regulates phototransduction in photoreceptor cells of the retina. Homologous proteins have been recently detected in other, non-photosensitive, cells of vertebrates, where they are thought to be associated with other systems of signal transduction. Proteins crossreactive with retinal arrestin were detected in soluble cell extracts from Nicotiana tabacum and Chlamydomonas reinhardtii by immunoblotting using several antibodies against arrestin. Variations of the immunoreactive protein pattern were associated with the growth cycle of tobacco cells. These observations suggest that analogs of arrestin exist in the vegetal kingdom, where they could be involved in transduction processes.

Animals↗

PubMed1991

The role of fibroblasts in organization and degradation of a fibrin clot.

Older clots become less sensitive to fibrin degradation than newly formed ones. A possible role for fibroblasts in this defective thrombus lysis was studied. A system has been developed in which different clones of fibroblasts were incorporated into a floating whole blood clot. The effect of the incorporated fibroblasts on clot lysis has been analyzed in relation to their basic characteristics: clot retraction, production of plasminogen activators (PAs) and their inhibitors (PAIs), and secretion of collagen. In neoplastic fibroblast-enriched clots, secretion of PA was associated with spontaneous lysis of a whole blood clot. Normal fibroblasts, secreting levels of PA and PAI similar to those of the cancer cells, did not induce spontaneous lysis of the clot. Moreover, these cells protected whole blood clot from thrombolysis by added PA. Our data show that the resistance to fibrin clot degradation induced by normal fibroblasts was mainly mediated by collagen secretion and deposition rather than PAI secretion or retraction of the clot. We suggest a key role for normal fibroblasts in the acquisition of resistance to proteolytic fibrin degradation of whole blood clots through the secretion of collagen.

Collagen↗

PubMed1990

Arrestin from nucleated red blood cells binds to bovine rhodopsin in a light-dependent manner.

Using a panel of monoclonal antibodies, it has previously been demonstrated that the cytosol of nucleated red cells (trout and turkey) contains a protein similar to arrestin, a soluble protein found so far only in the photosensitive cells and which, by binding to photoexcited rhodopsin, inhibits the phototransduction process. The role of this arrestin-like protein in non-photosensitive cells is questionable. In this report we present evidence that partially purified red blood cell arrestin (RBC arrestin) behaves functionally like bovine retinal arrestin: it binds to phosphorylated bovine rhodopsin only when this receptor has been photoactivated. Thus RBC arrestin and bovine retinal arrestin are closely related both structurally and functionally. By analogy with the function of retinal arrestin, it is proposed that RBC arrestin is involved in desensitization of membrane transport proteins and/or adrenergic receptors.

Animals↗

PubMed1990

Experimental autoimmune uveoretinitis: idiotypic regulation and disease suppression.

Experimental autoimmune uveoretinitis (EAU), a mostly T-cell dependent disease, was induced in laboratory animals by a single immunization with retinal extract or purified S-antigen in complete Freund's adjuvant. It can be prevented or suppressed by injections of either the autoantigen or monoclonal antibodies against the autoantigen. The suppression of EAU by these antibodies was associated with an anti-idiotypic antibody response. The inhibition of the pathogenic immune response by the antigen or the antibodies could be explained, according to Jerne's hypothesis of immunoregulation, by a disturbance of the network of idiotype and anti-idiotype interactions.

Animals↗

PubMed1990

Degradation of fibrinogen by tissue plasminogen activator. Consequences for fibrin polymerization.

In patients treated with tissue plasminogen activator (t-PA), there was a marked increase in concentration of fibrinopeptide A (fpA). The purpose of this study was to analyse the activation of coagulation in plasma treated in vitro by pharmacological doses of t-PA. From our results, it appears that fpA release due to direct interaction of fibrinogen with t-PA, in the absence of plasminogen, is very low and not observed with pharmacological doses of t-PA. In contrast in the presence of plasminogen, the release of fpA is much higher and induces fibrin formation concomitantly to fibrinogen degradation.

Biopolymers↗

PubMed1990

Evolutionary stability of fibrinogen epitopes implicated in fibrin polymerization and in fibrinolysis.

In this work, fibrinogen evolution was analysed by testing the reactivity of fibrinogen from different species with monoclonal antibodies against human fibrinogen fragment D. One epitope concerning the fibrin polymerization site 'a' and two epitopes responsible for tPA binding to fibrin were conserved in all mammalian fibrogens tested but not in crab coagulogen or pleurodella fibrinogen. In these two species, some epitopes which are not implicated in fibrinogen function were conserved. Therefore, we can conclude that polymerizing site 'a' and tPA binding sites have not been modified for at least 80 million years.

Animals↗

PubMed1990

Fibrin degradation products generation and fibrinopeptide A release in normal plasma incubated with thrombolytic agents: proposed mechanisms.

Clinical data have shown that the evaluation of fibrin degradation products (FbDP) does not reflect the efficiency of thrombolytic therapy in vivo. In this study, we found that the addition of plasminogen activators to normal plasma resulted in generation of FbDP and release of fibrinopeptide A (FpA) as shown by ELISA and HPLC. This FpA release was concomitant with fibrinogen degradation, and was not inhibited by thrombin inhibition or by prothrombin depletion in plasma. Thus, the increase in FpA did not result from coagulation activation and may result from the plasmin-induced release of FpA from fibrinogen degradation product E1. The generation of cross-linked FbDP after tPA addition occurred in normal plasma as well as in factor-XIII-deficient plasma and quickly reached a plateau. It was not inhibited by hirudin. Therefore FbDP in these plasmas probably derived from the plasmin degradation of cellular transglutaminase cross-linked fibrin/fibrinogen derivatives present in plasma.

Aprotinin↗

PubMed1990

S-antigen in non ocular tissues.

S-antigen has been considered a specific protein of photoreactive cells by immunohistochemical criteria. It was observed in the retina and pineal gland of all examined vertebrates as well as in photoreceptors of invertebrates, but not currently in other organs. However, contrary to pineal cells of poikilotherms and birds which are true or modified photoreceptors, mammalian pinealocytes are not photosensitive. Recent experiments demonstrated that S-antigen-like proteins are present in low amount in many other cells in the body. These proteins are characterized by the same migration pattern (the same molecular weight) as retinal S-antigen in SDS-electrophoresis and by their immunoreactivity with a panel of monoclonal and polyclonal antibodies to S-antigen. These cells are not photosensitive, but are controlled by beta adrenergic, G-protein mediated adenylate cyclase system, a transduction system that shares many structural and functional homologies with visual transduction. S-antigen (arrestin) plays a regulatory role in phototransduction in rods by desensitizing rhodopsin. In the mammalian pineal and in other cells or tissues, S-antigen, or a family of structurally related proteins, could similarly be involved in the regulation of chemical signal transduction. Whether any systemic pathology is associated with uveoretinitis and pinealitis after S-antigen immunization deserves further investigations.

Animals↗

PubMed1990

[Secretion of plasminogen activators and their inhibitors in corneal fibroblasts. Modification of this secretion in Schnyder's lens corneal dystrophy].

In this study, we have shown that the secretion of plasminogen activators (PA) by corneal fibroblasts from Schnyder dystrophy is much lower than that secreted by normal corneal fibroblasts. This defective secretion of PA was noted both in the supernatant of cell culture and on the cell surface. This anomaly is found in cultured fibroblasts and therefore is not related to environment modification. Since PA was implicated in remodeling of extracellular matrix, we hypothesized that this anomaly should be responsible for the corneal dystrophy.

Cells, Cultured↗

PubMed1989

Immunological detection of arrestin, a phototransduction regulatory protein, in the cytosol of nucleated erythrocytes.

Cytosolic extracts of trout and turkey erythrocytes were tested for their immunoreactivity with polyclonal and monoclonal antibodies to retinal arrestin (S-antigen), a cytosolic protein of photoreceptor cells involved in the desensitization of rhodopsin. After adsorption or immunoaffinity chromatography of the extracts, these antibodies specifically recognized a protein having a molecular weight similar to that of retinal arrestin. Because the G-protein-mediated transduction systems, such as visual and beta-adrenergic systems, display a high degree of structural and functional homology, the presence of arrestin-like proteins in non-photosensitive cells suggests that these proteins are involved in the transduction of chemical signals, with a possible role in receptor desensitization.

Animals↗