Search PubMed⌕ Search

Biomedical subjects

Z Fishelson

Publications and source records attributed to Z Fishelson.

At least 19 recordsLinked to original sources
PubMed1994

Functional and antigenic similarities between a 94-kD protein of Schistosoma mansoni (SCIP-1) and human CD59.

Schistosomiasis is a parasitic disease affecting approximately 200 million people, primarily in the third world. Schistosoma mansoni, one of the causative agents of this disease, parasitize the human mesenteric and portal blood systems while successfully evading host immune responses. During parasite penetration into the mammalian host and shortly afterwards, the larvae rapidly convert from being sensitive to being resistant to C-mediated killing. Treatment of the C-resistant parasitic forms with trypsin renders the parasite susceptible to C attack, thus indicating the presence of C inhibitory protein(s) on the parasite surface. We describe here an intrinsic schistosome C inhibitory protein (SCIP-1) that exhibits antigenic and functional similarities with the human C-inhibitor CD59. Like CD59, SCIP-1 is capable of inhibiting formation of the C membrane attack complex (MAC), probably by binding to C8 and C9 of the C terminal pathway. In addition, SCIP-1 is apparently also membrane-anchored via glycosyl phosphatidylinositol as it can be specifically released with phosphatidylinositol-specific phospholipase C. Soluble SCIP-1, partially purified from Nonidet P-40 extracts of schistosome tegument is capable of inhibiting hemolysis of sensitized sheep erythrocytes and of rabbit erythrocytes by human C. Anti-human CD59 antibodies block this activity of SCIP-1 and in addition, upon binding to intact parasites, render them vulnerable to killing by human and guinea pig C. SCIP-1 is located on the surface of C-resistant forms of the parasite, i.e., 24-h cultured mechanical schistosomula and in vivo-derived adult worms as revealed by immunofluorescence and immunogold electron microscopy studies. These results identify one of the mechanisms schistosomes use to escape immune attack.

Animals↗
PubMed1992

Sublytic complement attack protects tumor cells from lytic doses of antibody and complement.

Sublytic doses of the membrane attack complex (MAC) of complement are known to exert multiple stimulatory effects on metabolically active cells. Results presented herewith demonstrate that pretreatment of the human leukemic cells K562 and HL-60 with sublytic doses of antibody and normal human serum protects them from lytic complement concentrations, a phenomenon proposed to be called "complement-induced protection". C7- and C8-deficient human sera are ineffective in inducing resistance unless they are reconstituted with purified human C7 and C8, respectively. The complement-induced protection is inhibitable by actinomycin D and cycloheximide indicating that the increased complement resistance depends on RNA and protein synthesis triggered by the sublytic complement doses. Free extracellular Ca2+ is also required to achieve maximal protection, indicating a role for Ca2+ ions in the cell stimulatory events which culminate in increased complement resistance. Quantitative analysis of bound complement components indicated that similar amounts of C3 and C9 molecules are deposited on "protected" and control cells during complement activation. The "protected" K562 and HL-60 cells regain sensitivity to lytic MAC doses after about 8 or 3 h, respectively, of culture in growth medium, in the absence or presence of actinomycin D and cycloheximide. The "induced protection" is not species restricted and protection from human complement can be induced in K562 cells by treatment with sublytic doses of antibody and rabbit or guinea pig sera.

Animals↗
PubMed1992

Schistosoma mansoni: cell-specific expression and secretion of a serine protease during development of cercariae.

Eukaryotic serine proteases are an important family of enzymes whose functions include fertilization, tissue degradation by neutrophils, and host invasion by parasites. To avoid damaging the cells or organisms that produced them, serine proteases must be tightly regulated and sequestered. This study elucidates how the parasitic blood fluke Schistosoma mansoni synthesizes, stores, and releases a serine protease during differentiation of its invasive larvae. In situ hybridization with a cDNA probe localized the protease mRNA to acetabular cells, the first morphologically distinguishable parasite cells that differentiate from the embryonic cell masses present in the intermediate host snail. The acetabular cells contained vimentin but not cytokeratins, consistent with a mesenchymal, not epithelial, origin. Antiprotease antibodies, localized by immunoperoxidase, showed that the protease progressively accumulated in these cells and was packaged in vesicles of three morphologic types. Extension of cytoplasmic processes containing protease vesicles formed "ducts" which reached the anterior end of fully differentiated larvae. During invasion of human skin, groups of intact vesicles were released through the acetabular cytoplasmic processes and ruptured within the host tissue. Ruptured protease vesicles were noted adjacent to degraded epidermal cells and dermal-epidermal basement membrane, as well as along the surface of the penetrating larvae themselves. These observations are consistent with the proposed dual role for the enzyme in facilitating invasion of host skin by larvae and helping to release the larval surface glycocalyx during metamorphosis to the next stage of the parasite.

Animals↗
PubMed1992

Complement membrane attack complexes induce in human leukemic cells rapid expression of large proteins (L-CIP).

The effect of sublytic doses of the complement membrane attack complexes (MAC) on protein synthesis in human leukemic cells was examined. As shown herein, rapid protein synthesis is evident in K562 erythroleukemic cells upon exposure to sublytic complement doses. Analysis of cell extracts by SDS-PAGE revealed high molecular weight proteins which appeared in the cells already after 15 min treatment with complement at 37 degrees C, reaching a maximal level after 40-50 min. These large complement-induced proteins (L-CIP) were clearly observed in gels stained by Coomassie blue and in autoradiograms following [35S]-Met or [3H]-Leu incorporation. Rabbit antibodies prepared against L-CIP were reactive in immunoassays with extracts of MAC-treated cells but not of non treated cells. They also bound to the surface of intact K562 cells (as determined by immunofluorescence), but only after treatment of the cells with complement. Both heterologous (rabbit and guinea pig) and homologous (human) sera induced L-CIP synthesis. The induction of L-CIP was indeed mediated by the complement MAC since L-CIP could not be detected in K562 cells exposed to heat-inactivated human serum or C6-deficient rabbit serum. Similarly, C7- or C8-deficient human sera could not induce L-CIP production unless they were reconstituted with purified human C7 or C8, respectively. The synthesis of L-CIP was largely inhibited by the protein synthesis inhibitors cycloheximide and puromycin and partially inhibited by the RNA synthesis inhibitor actinomycin D. L-CIP was similarly induced in two other human leukemic cell lines, U937 and HL-60, but not in K562/S, a subline of K562 which is highly sensitive to complement damage. These results are discussed with respect to the resistance of leukemic cells, and nucleated cells in general, to complement-mediated immune damage.

Cell Death↗
PubMed1992

The human lymphokine leukoregulin induces cell resistance to complement-mediated lysis.

Leukoregulin (LR) is a lymphokine secreted by human natural killer (NK) cells. Its effect on the susceptibility of K562 human erythroleukemic cells to lysis by antibody and complement was examined. As reported here, treatment of K562 cells with LR for 60 min at 37 degrees C confers on them resistance to complement damage. The LR-induced state of complement resistance is transient and the cells recover within 4-6 h unless a second dose of LR is added. The protective action of LR was observed using both conventional 51Cr-release and trypan blue inclusion assays. The protein synthesis inhibitors puromycin and cycloheximide and the protein kinase inhibitors tamoxifen, polymyxin B and W-7, could each block this action of LR. Fewer membrane attack complexes were found, following complement activation, on LR-treated than control cells. These results suggest that LR increases the capacity of K562 cells to down-regulate complement activation or repair the complement damage, possibly by inducing synthesis of defense proteins and/or activation of protective protein kinases.

Antibodies, Neoplasm↗
PubMed1991

Leishmanial protein kinases phosphorylate components of the complement system.

Externally oriented protein kinases are present on the plasma membrane of the human parasite, Leishmania. Since activation of complement plays an important role in the survival of these parasites, we examined the ability of protein kinases from Leishmania major to phosphorylate components of the human complement system. The leishmanial protein kinase-1 (LPK-1) isolated from promastigotes of L. major was able to phosphorylate purified human C3, C5 and C9. Only the alpha-chain of C3 and C5 was phosphorylated. The beta-chain appeared not to be a substrate for this enzyme. C3b which is formed by proteolytic cleavage of C3 was not phosphorylated by LPK-1. Trypsin treatment of phosphorylated C3 (P-C3) resulted in the disappearance of 32P from the alpha-chain. This was correlated with the conversion of the C3 alpha-chain to the alpha'-chain of C3b, and the appearance of a 9 kDa 32P fragment comigrating with the C3a fragment of C3. P-C3 was more resistant to cleavage by trypsin than nonphosphorylated C3. LPK-1 phosphorylated purified C3a and two synthetic peptides, C3a21R and YA-C3a10R, derived from its COOH-terminal end, which contain the C3a binding site to leukocytes and platelets. LPK-1 did not phosphorylate C3a8R. Phosphoamino acid analysis of the synthetic peptides indicated that serine 71 of C3a was phosphorylated by LPK-1. Treatment of C3 with either methylamine or freeze-thaw C3 (H2O) prevented phosphorylation by the LPK-1 suggesting that substrate conformation may be involved in recognition by the leishmanial enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Resistance to NK cell-mediated cytotoxicity (in K-562 cells) does not correlate with class I MHC antigen levels.

Natural Killer (NK) cells probably function as an early line of defense against virus-infected cells and tumor cells. In all cases, the killing by NK cell-mediated cytotoxicity (NK-CMC) is not MHC-restricted and the factors which determine the sensitivity to NK-CMC have not yet been identified. A positive correlation between resistance to NK-CMC and the level of class I MHC antigen (MHC I) expression on target cells has been reported in many studies, and in some cases a functional linkage between the two has been claimed. Several other studies have shown that there is no such correlation. By employing several experimental systems, we demonstrate here a lack of correlation between the level of MHC I and the sensitivity of K-562 cells to NK-CMC. Transfer of MHC I to MHC I-negative cells via vesicles had no effect on their resistance to NK-CMC. In addition, a decrease in resistance to NK-CMC and increase of MHC I levels was observed following target-cell membrane modulation by both application of cholesterol and hydrostatic pressure. Finally, no correlation between sensitivity to NK-CMC and MHC I expression was found in three sublines of K-562 cells. Since NK-CMC is a multistage process, it is concluded that components other than class I MHC antigens have a more prominent role in modulating the sensitivity of target cells to NK-CMC.

Cell Death↗
PubMed1991

Heterotypic leukocyte aggregation in the peripheral blood of patients with leukemia, inflammation and stress.

This study deals with the question of whether the aggregates of leukocytes in the peripheral blood are homo- or heterotypic. One hundred-fifty individuals with leukemia, inflammation, and physical and mental stress, were examined. It was found that the various cell populations of the peripheral blood are represented in the aggregates and that aggregates are generally heterotypic. Normal and malignant leukocytes were noted in aggregates of patients with leukemia, suggesting that adhesive mechanisms are similar for both normal and malignant leukocytes. This was also supported in two animal models, one with leukocytosis of normal cells and the other with leukocytosis of leukemic cells, in which the state of leukocyte adhesiveness/aggregation in the peripheral blood correlated with tissue leukostasis. The possibility exists that "non specific stickers", present in the peripheral blood, promote interactions between the white blood cells, normal and malignant, and between these cells and the endothelium.

Adolescent↗
PubMed1990

Potentiation of NK cytotoxicity by antibody-C3b/iC3b heteroconjugates.

The interaction of two Burkitt lymphoma lines, Raji and Rael, with human C and NK cells was analyzed. Raji cells activate the alternative C pathway (ACP) and then bind C3 fragments. Consequently, the cells become more sensitive to lysis by CR3-bearing NK cells but not to C lysis. In contrast, Rael cells are poor ACP activators, do not bind C3 fragments, and are therefore resistant to C-dependent NK lysis. As suggested earlier, the difference between Raji and Rael could be attributed to the presence or absence of CR2, respectively, on their surface. To potentiate C- and NK-dependent lysis of target cells, we generated heteroconjugates composed of a murine antitransferrin receptor mAb and of human C C3b or iC3b. Antibody-C3b conjugates induced C3 deposition on Rael cells and elevated C3 deposition on Raji cells in human serum. Both Raji and Rael cells coated with antibody-C3b conjugates were efficiently lyzed by the cytolytic ACP in human serum. This conjugate had a small enhancing effect on target cell lysis by NK cells which could be markedly increased by combined treatment of the target cell with antibody-C3b conjugate and C5-depleted human serum. On the other hand, antibody-iC3b conjugates efficiently potentiated lysis of target cells by NK cells in the absence of serum. The iC3b-directed cytotoxicity was mediated by CR3-bearing NK effector cells. Anti-C3 but not anti-mouse Ig antibodies abrogated the activity of the antibody-iC3b conjugate. These results further demonstrate that NK cytotoxicity may be potentiated by opsonizing the target cells with C3 fragments and suggest that antibody-C3b/iC3b conjugates could be potent tools for targeting and potentiation of the lytic action of both C and NK cells against tumor cells.

Antigen-Antibody Complex↗
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

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↗