Search PubMed⌕ Search

Biomedical subjects

Z Fishelson

Publications and source records attributed to Z Fishelson.

At least 55 records · Page 3Linked to original sources
PubMed1990

Complement regulation on the surface of cultured schistosomula and adult worms of Schistosoma mansoni.

Cercaria and freshly prepared schistosomula of Schistosoma mansoni are highly sensitive to complement. However, early in their maturation, the schistosomula become resistant to complement killing. This conversion is preceded by a rapid and massive release of several acetabular proteases and of the glycocalyx coat. Thus, shedding of the glycocalyx which is a major immunogen and a strong activator of the alternative pathway of complement permits the parasite to escape immune damage. Mechanically transformed schistosomula, which were cultured in a defined synthetic medium and developed complement resistance, could be converted by proteolysis to complement sensitivity. Trypsin and pronase markedly increased the susceptibility of cultured schistosomula to complement. The trypsin-induced complement sensitivity persisted for at least 19 h without recovery of resistance. Similar treatment with trypsin produced complete killing of adult worms by complement in absence of antibodies. Efficient killing was obtained with normal human serum (NHS), with normal guinea pig serum (GpS), and with C4-depleted HS and C4-deficient GpS indicating that the killing was mediated by the cytolytic alternative pathway of complement. Larger quantities of C3b with intact alpha' chain could be demonstrated on trypsin-treated than on non-treated schistosomula. Antibodies which were raised in rabbits by immunization with the trypsin-released material bound to cultured (non-treated) schistosomula and to adult worms, and induced their killing in GpS and C4-deficient GpS. These results suggest that following release of the glycocalyx, the transforming schistosomula of S. mansoni spontaneously express a complement regulatory protein(s). A similar regulator is postulated to be present on the surface of adult worms. Such regulatory molecules may serve as good targets for immunotherapy, since antibodies directed to them will inhibit their regulatory activity and thus potentiate in vivo the lytic action of complement.

Animals↗
PubMed1990

Prevalence of hereditary properdin, C7 and C8 deficiencies in patients with meningococcal infections.

High incidence of hereditary complement (C) deficiencies was found among 101 patients who had a meningococcal disease. This study revealed 11 non-related patients with complete C deficiency: five deficient in C7, three in C8, two in properdin and one in C2. Additional C-deficient individuals, most of them with no history of severe bacterial infections, were detected in family studies. The C8-deficient patients were found to have a selective deficiency of the C8-beta subunit and a reduced expression of the alpha/gamma subunit. Only a few families with properdin deficiency have been described so far. However, it is likely that frequent analysis of the activity of the alternative C pathway in survivors of severe bacterial infections will disclose numerous properdin-deficient patients. All our C7-, C8- and properdin-deficient patients are Sephardic Jews whose families originated from Morocco, Yemen (C7 and C8 deficient) or Tunisia (properdin deficient). This and other findings indicate that the type of complement abnormality found in association with meningococcal infections varies with the ethnic origin of the patient.

Adolescent↗
PubMed1990

Schistosoma mansoni: localization of the 28 kDa secreted protease in cercaria.

Monospecific rabbit antibodies were utilized to localize the 28 kDa serine protease which is released from transforming schistosomula of Schistosoma mansoni in cercariae and freshly transformed schistosomula. This protease exerts two postulated activities, degradation of connective tissue proteins thus promoting skin penetration and release of the cercarial glycocalyx leading to accelerated schistosomular transformation. Upon immunogold labelling of cercarial cryosections, the 28 kDa protease was found stored in both the preacetabular and postacetabular glands. This enzyme was also detected in the cercarial glycocalyx by immunogold and immunofluorescence labelling and by its proteolytic activity. Following transformation and shedding of the glycocalyx, the same 28 kDa protease was found on the surface membrane of transformed schistosomula which are resistant to immune damage. It is suggested that the 28 kDa membrane protease which cleaves in vitro the complement proteins C3, C3b and C9, may promote in vivo immunoresistance of S. mansoni.

Animals↗
PubMed1989

Targeting of complement to tumor cells by heteroconjugates composed of antibodies and of the complement component C3b.

Tumor cells have adapted several strategies which permit them to grow in an immunologically hostile environment. The C system can potentially destroy these cells; however, its action needs to be specifically potentiated on the surface of the tumor cells. To this end, a heteroconjugate composed of a mouse mAb and of the human C3b C component has been generated by using the heterobifunctional reagent N-succinimidyl-3-(2-pyridyldithio)propionate. The two mAb which were used in this study are V1-10 and TIB219 which bind to the human and mouse transferrin receptors, respectively. The mAb-C3b conjugates were purified by gel filtration and were each composed of one mAb and one C3b. They bound to the human K562 and HL60 or mouse ALB1 cell lines and amplified the killing of these cells by C from 10 to 15% to 70 to 100%. Fresh normal human or mouse sera were used as a source of C. The mAb-C3b conjugates activated primarily the alternative pathway of C since only C3 and factor B but not C4 were cleaved in the sera. After disulfide-linking to the mAb, the C3b became highly resistant to inactivation by factors H and I, probably due to its reduced factor H binding capacity. On the other hand, the conjugated C3b bound factor B better than free C3b and produced more C3 convertases which expressed increased stability. These results suggest that mAb-C3b conjugates may serve as an effective tool for the specific activation of the cytolytic C system on selected cells. As such, they may be used in vitro or in vivo to target the autologous C to tumor cells or to lymphocytes and may promote tumor immunotherapy.

Animals↗
PubMed1989

Complement and parasitic trematodes.

The complement (C) system acts as a barrier to protect our bodies against invading pathogens. It may react to cytophilic antibodies or directly to foreign molecules presented by the intruder. As well as their cytotoxic activity, C components can attract and attach leucocytes to the surface of the foreign body, and activate them to kill it. Zvi Fishelson describes various strategies used by a parasitic trematode to escape immune damage in the face of potent immune surveillance by C and other effector mechanisms.

Journal Article↗
PubMed1989

Killing of human tumor cells by antibody C3b conjugates and human complement.

To potentiate the lytic action of complement on tumor cells, we have constructed heteroconjugates composed of monoclonal antibody and of the human C3b component of complement. The conjugates were formed efficiently using the heterobifunctional cross-linking reagent SPDP. The monoclonal antibody-C3b conjugate promoted the killing of K562 tumor cells by normal human serum. Treatment of the tumor cells with the monoclonal antibody and normal human serum resulted in 10-15% lysis. However, following pretreatment of the cells with antibody-C3b conjugates, their lysis by normal human serum increased to 70%. The conjugate activated selectively the alternative pathway of complement and the C3b component in the conjugate was highly resistant to cleavage and inactivation by the complement regulatory proteins Factors H and I. These results suggest that the coupling of C3b molecules to monoclonal antibodies anti-unique tumor antigens produces a potent complement-activating reagent which may act specifically on tumor cells and promote cancer therapy.

Antibodies, Monoclonal↗
PubMed1989

Visualization of vascular platelet aggregation by plastic embedding and light microscopy.

Previous studies have indicated that platelets play a role in inflammation and microvascular damage but routine histologic preparations do not permit clear visualization of the platelets in tissues. Plastic embedding was used in this study to demonstrate platelet aggregates in the pulmonary vasculature of mice exposed to complement activation. The degree of platelet aggregation in the excised lungs was graded semiquantitatively in a total of 75 mice. Control Balb/c mice had a mean aggregation score of 0.16 while mice which received 0.3 ml zymosan-activated plasma (ZAP) intravenously (iv) had a score of 2.2. Injection of 0.3 or 0.4 ml of ZAP to which epsilon-aminocaproic acid was added prior to incubation with zymosan resulted in a score of 2.6 or 4.7 respectively. Balb/c (C5 sufficient) and AKR/J (C5 deficient) mice injected iv with 1 mg zymosan had scores of 2.9 and 3.2, respectively. Cobra venom factor (CVF) injected iv to Balb/c mice induced a dose-dependent aggregation. Taken together, these results confirm that complement activation products can mediate intrapulmonary platelet aggregation and they also demonstrate the suitability of plastic embedding for visualization of intravascular platelet aggregates under light microscopy.

Animals↗
PubMed1988

Proteases secreted by transforming schistosomula of Schistosoma mansoni promote resistance to killing by complement.

Early events in the transformation of schistosomula of Schistosoma mansoni include shedding of the glycocalyx and conversion of the parasite from sensitive to resistant to complement-mediated killing. This is accompanied by a release of proteolytic activity which occurs at the same rate as the first two phenomena and is also complete within 1 h of culture at 37 degrees C in defined synthetic medium. Two serine proteases, of 28 kDa and a 60 kDa, were purified to homogeneity from the culture medium of transforming schistosomula; the purification steps and the initial characterization of these proteases are reported elsewhere. Both proteases accelerated the release of surface molecules from the schistosomula; however, the effect of the 28-kDa protease was much more pronounced. Qualitative analysis of the material cleaved from the schistosomula by the purified proteases on SDS-PAGE revealed a fragmentation pattern identical with that of the material shed spontaneously from transforming schistosomula. This strongly suggests that the 28-kDa and 60-kDa proteases contribute physiologically to the release of the schistosomular surface molecules including the high Mr glycocalyx. The activity of the two proteases was inhibited by PMSF. Freshly transformed schistosomula treated shortly with the purified 28-kDa protease produced a lower C consumption and became more refractory to C killing. Both consumption and killing were mediated by the alternative pathway of C in the absence of antibodies. These results postulate a role for proteases secreted by transforming schistosomula in the release of schistosomular surface molecules which activate C. This may serve as an escape mechanism from C damage employed by transforming schistosomula.

Animals↗
PubMed1988

Purification and characterization of proteases secreted by transforming schistosomula of Schistosoma mansoni.

Schistosomula of Schistosoma mansoni which are mechanically transformed at 4 degrees C and are then incubated at 37 degrees C in defined medium spontaneously secrete two proteases, a major one of 28 kDa and a minor one of 60 kDa. These were purified by ion exchange chromatography on DEAE-cellulose and gel filtration on Ultrogel AcA 54 with yields of 33% and 29%, respectively. Both appeared as single bands by silver staining following sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis. The 28 kDa protease is a glycoprotein that has a pI of 11 or higher and an optimal activity around pH 9.0. It cleaves casein, gelatin and human C3 and C3b. It is metal-ion independent and is inhibited by diisopropyl fluorophosphate, phenylmethanesulfonyl fluoride, soy-bean trypsin inhibitor, alpha 1 antitrypsin, Zn2+ ions, sodium dodecyl sulphate and normal human serum. The 60 kDa protease is a glycoprotein with a pI of 9.2. It can also cleave casein and gelatin and its activity is inhibited by phenylmethanesulfonyl fluoride but not by diisopropyl fluorophosphate or sodium dodecyl sulphate. We suggest that these proteases may play a role during cercarial penetration of the skin and in shedding of the cercarial glycocalyx.

Animals↗
PubMed1988

Synergism between zymosan-activated serum and heparin in the induction of polymorphonuclear leukocyte aggregation.

During the course of extracorporeal circulation, leukocyte aggregation is known to occur in some patients. This is attributed to complement activation and release of the chemotactic factor C5a. We investigated the effect of heparin on in vitro complement induced aggregation of polymorphonuclear leukocytes (PMNAGG), since most patients undergo heparinization during the extracorporeal circulation. Our results indicate that sub-aggregating concentrations of zymosan-activated serum (ZAS) enhance heparin-induced PMNAGG and that sub-aggregating amounts of heparin increase the aggregation induced by ZAS. Heat inactivation of the serum prior to zymosan activation abrogated the aggregating activity of the ZAS. Furthermore, the combined ZAS and heparin-induced PMNAGG was partially inhibited by specific antibodies to C5a but not to C3a. Therefore, we suggest that heparin and C5a may have a synergistic effect on the aggregation of polymorphonuclear leukocytes. These data might be relevant to situations in which patients are subjected to extracorporeal circulation.

Cell Aggregation↗
PubMed1987

Regulation of the alternative pathway of complement by pH.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic anemia. The abnormal PNH erythrocytes are highly susceptible to complement-mediated lysis in vitro, especially at pH 6.4. Lysis has been shown to be due to alternative pathway activation. The purpose of this study was to determine why lysis of PNH erythrocytes is increased at acidic pH. The results presented demonstrate that at pH 6.4: binding of C5 and Factor B to C3b deposited on human erythrocytes is markedly enhanced; generation of the two C3 convertases, C3(H2O), Bb and C3b,Bb is increased; and control of C3b on human erythrocytes by CR1 and Factor I is diminished. In addition, it was found that rabbit erythrocytes, which activate the human alternative pathway, are also lysed much better at pH 6.4 than at pH 7.4. These results indicate that the optimal pH for the initiation and amplification of the alternative complement pathway, and probably also for the activation of the membrane attack complex, is 6.4.

Complement Activation↗
PubMed1987

C3 convertase of the human alternative pathway of complement: modulation of enzyme activity and stability by mouse monoclonal antibodies to Bb.

To further characterize functional sites on C3b,Bb, and C3 convertase of the alternative pathway of complement, we examined the effect of four monoclonal antibodies on its activity and stability. These antibodies recognized antigenic epitopes on human Bb which were not fully exposed in intact factor B. Three of the monoclonal antibodies inhibited lysis of rabbit erythrocytes by normal human serum in the presence of Mg2+ and EGTA. Two of these antibodies markedly inhibited the activity of purified C3b,Bb deposited on rabbit erythrocytes. However, all four monoclonal antibodies increased the half-life of the C3 convertase. Thus, these results demonstrate that binding of antibodies to Bb may concomitantly stabilize C3b,Bb and abate its activity. It is likely that such antibodies induce in Bb conformational changes which increase the C3b,Bb complex stability but may also hinder its catalytic site.

Antibodies, Monoclonal↗
PubMed1987

Regulation of the alternative pathway of human complement by C1q.

The interaction of C1q with C3b and its effect on C3b activities in the alternative pathway of complement (APC) have been studied. Purified C1q markedly inhibited C3b deposition on and lysis of rabbit erythrocytes by the isolated cytolytic APC. It also blocked formation of the C3 convertase, C3b, Bb as well as binding of Factors B and H to sheep erythrocytes (E) bearing C3b. The direct and specific binding of C1q to C3b was clearly demonstrated using the hemagglutination technique at low ionic strength (0.1 M NaCl). C1q concns of 2 micrograms/ml and higher agglutinated, in a dose-dependent fashion, EC3b but not E, EC3bi or EC3d. Addition of C1r and C1s to C1q and formation of C1 did not affect its capacity to agglutinate EC3b. The C1q-mediated agglutination of EC3b was inhibited by EDTA, MgEGTA, C3b and Factor B but not by native C3 or collagen. Heating C1q (56 degrees C) markedly potentiated its agglutinating activity whereas collagenase-treated C1q lost most of its activity. Taken together, these results suggest that C1q binds through its "heads" and in the presence of calcium ions to a site on C3b that is adjacent to the Factor B and Factor H binding sites. This interaction may down-regulate the activity of the alternative pathway of complement on surfaces which activate both the classical and alternative pathways of complement.

Animals↗
PubMed1987

The phenomenon of leukergy: induction and detection of leukocyte aggregation in whole human blood.

Leukocyte aggregation is involved in the generation of vascular damage during various inflammatory conditions. So far, in vitro leukocyte aggregation has been studied by mixing patients' plasma or serum with leukocytes of a normal donor in a platelet aggregometer. We evaluated the leukergy phenomenon, that is, the occurrence of aggregated leukocytes in peripheral blood of patients with inflammatory disorders, as an alternative tool to the former method. Leukocyte aggregation could be induced by zymosan-activated plasma, phorbol myristate acetate, and formyl-methionyl-leucyl-phenylalanine, as well as by the calcium ionophore A23187 in vitro in whole human blood. This aggregation was blocked by various lipoxygenase and cyclooxygenase pathway inhibitors. Leukergy was diagnosed in peripheral blood of patients with inflammatory disorders and was generally not associated with elevated concentrations of immune complexes, lactoferrin, C3a des Arg, or C5a des Arg. To the best of our knowledge, this is the first report on leukocyte aggregation studies performed in whole blood. Such study permits evaluation of the aggregation phenomena of leukocytes in their natural milieu. Furthermore, it is possible with this method to obtain direct visualization of leukocytic aggregates in the peripheral blood of patients. The significance of our results and their possible implications are discussed in light of the pertinent literature.

Adult↗
PubMed1986

Schistosoma mansoni: killing of transformed schistosomula by the alternative pathway of human complement.

The interaction of mechanically transformed schistosomula of Schistosoma mansoni with the alternative pathway of human complement was studied in vitro. To detect early changes in transformation, the schistosomula were prepared at a low temperature and used immediately. As shown previously, freshly transformed schistosomula were highly susceptible to killing by normal human serum and by C4-depleted normal human serum. This serum activity was concentration dependent and was markedly reduced on a twofold serum dilution. Upon incubation at 37 C in defined synthetic medium, schistosomula rapidly became refractory to killing by the alternative pathway of complement. After 1 hr of incubation at 37 C, the percentage of schistosomula which were resistant to killing increased from 16 to 85. This conversion was accompanied by a fivefold decrease in deposition of C3b on schistosomula which had been exposed to 37 C for 1 hr and then further incubated with C4-depleted normal human serum. The following events occurred concomitantly during incubation of freshly transformed schistosomula at 37 C with a half-life of 30-60 min: (1) Decrease in activation and consumption of the alternative pathway of complement by schistosomula; (2) appearance of a strong complement consuming activity in the supernatant of incubating schistosomula; and (3) shedding of protein- and carbohydrate-containing substances from the surface of schistosomula into the supernatant. Isolated external membranes of freshly transformed schistosomula consumed the alternative pathway of complement to a greater extent than membranes of schistosomula preincubated in medium at 37 C. The results demonstrate that transformed schistosomula acquire resistance to complement killing via the alternative pathway by shedding complement-activating substances.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Residual hemolytic and proteolytic activity expressed by Bb after decay-dissociation of C3b,Bb.

Bb (Mr = 63,000) is the catalytic site-bearing subunit of the C3 convertase of the alternative complement pathway, C3b,Bb, which is dissociated from the complex upon decay of the enzyme. Because purified Bb induced certain leukocyte activities, we examined whether it expresses residual hemolytic or proteolytic activity. Hemolytic activity of Bb was tested by using Factor B- or Factor D-depleted normal human serum and rabbit or sheep erythrocytes. Proteolytic activity of Bb was assessed by using purified C3 or C5 as substrates and SDS-PAGE to detect protein cleavage. Bb expressed metal-dependent hemolytic activity that was approximately 100-fold lower than that of Factor B. This activity could be inhibited by Factor H and enhanced by properdin. Low but statistically significant binding of 125I-labeled Bb to C3b on erythrocytes was demonstrated. Monoclonal antibodies that bind to Bb but not to intact Factor B inhibited the Bb hemolytic activity. Purified Bb cleaved C3 to C3a and C3b, as evidenced by the appearance of the alpha'-chain of C3b. It also cleaved C5 to C5a and C5b when cobra venom factor was present in the reaction mixture. Metal ions were required for expression of proteolytic activity, and Ni supported the activity better than Mg. These results indicate that decayed Bb has residual C3 and C5 cleaving activity and hemolytic activity, expression of which appears to require its association with C3b, C3(H2O), or cobra venom factor. These observations may aid in explaining the mechanism of action of Bb on leukocytes.

Antibodies, Monoclonal↗