Phase IV clinical trial with a single treatment arm to evaluate bronchopulmonary penetration of isavuconazole in pulmonary transplant recipients (PBISA01): Study protocol clinical trial. (Preprint)

Background

Aspergillosis is the most frequently observed invasive fungal disease (IFD) in lung transplant recipients. Isavuconazole (ISA) has shown a better safety profile and noninferiority to voriconazole in the treatment of patients with IFD.

Objective

The aim of this study is to describe the bronchopulmonary pharmacokinetic profile of oral ISA by analyzing the degree of penetration in the epithelial lining fluid and alveolar macrophages in patients receiving lung transplantation with a diagnosis of IFD.

Methods

A total of 12 patients aged ≥18 years receiving a lung transplant with an IFD diagnosis and indication for ISA treatment and follow-up bronchoscopy will be included in the study. After 5 days of treatment with ISA and before the treatment is discontinued, the patients will be randomized (1:1:1:1) to perform the scheduled bronchoscopy at various times after the administration of ISA (2, 4, 8, and 12 hours). In total, 4 blood samples will be obtained per patient: at 72 hours after treatment initiation, on the day of the bronchoscopy, at the time of the bronchoalveolar lavage (simultaneously), and at 7 days after treatment initiation, to analyze tacrolimus and ISA plasma levels. ISA concentrations will be measured in plasma, epithelial lining fluid, and alveolar macrophages by a high-performance liquid chromatography/UV coupled to fluorescence method.

Results

Enrollment for the PBISA01 trial began in October 2020 and was completed in October 2021. All samples will be analyzed once recruitment is complete, and the results are expected to be published in October 2022.

Conclusions

There are no clinical studies that analyze the bronchopulmonary penetration of ISA. Bronchoalveolar lavage performed routinely in the follow-up of lung transplant recipients constitutes an opportunity to analyze the bronchopulmonary penetration of ISA.

Trial Registration

European Clinical Trials Register 2019-004240-30; www.clinicaltrialsregister.eu/ctr-search/trial/2019-004240-30/ES

International Registered Report Identifier (IRRID)

DERR1-10.2196/37275

Blebbistatin and blebbistatin-inactivated myosin II inhibit myosin II-independent processes in Dictyostelium

Blebbistatin, a cell-permeable inhibitor of class-II myosins, was developed to provide a tool for studying the biologic roles of myosin II. Consistent with this use, we find that blebbistatin inhibits three myosin II-dependent processes in Dictyostelium (growth in suspension culture, capping of Con A receptors, and development to fruiting bodies) and does not inhibit growth on plates, which does not require myosin II. As expected, macropinocytosis (myosin I-dependent), contractile vacuole activity (myosin V-dependent), and phagocytosis (myosin VII-dependent), none of which requires myosin II, are not inhibited by blebbistatin in myosin II-null cells, but, unexpectedly, blebbistatin does inhibit macropinocytosis and phagocytosis by cells expressing myosin II. Expression of catalytically inactive myosin II in myosin II-null cells also inhibits macropinocytosis and phagocytosis. Both blebbistatin-inhibited myosin II and catalytically inactive myosin II form cytoplasmic aggregates, which may be why they inhibit myosin II-independent processes, but neither affects the distribution of actin filaments in vegetative cells or actin and myosin distribution in dividing or polarized cells. Blebbistatin also inhibits cell streaming and plaque expansion in myosin II-null cells. Our results are consistent with myosin II being the only Dictyostelium myosin that is inhibited by blebbistatin but also show that blebbistatin-inactivated myosin II inhibits some myosin II-independent processes and that blebbistatin inhibits other activities in the absence of myosin II.

Cell aggregation by scaffolded receptor clusters

The aggregation of cells by lectins or antibodies is important for biotechnological and therapeutic applications. One strategy to augment the avidity and aggregating properties of these mediators is to maximize the number of their ligand binding sites. The valency of lectins and antibodies, however, is limited by their quaternary structures. To overcome this limitation, we explored the use of polymers generated by ring-opening metathesis polymerization (ROMP) as scaffolds to noncovalently assemble multiple copies of a lectin, the tetravalent protein concanavalin A (Con A). We demonstrate that complexes between Con A and multivalent scaffolds aggregate cells of a T cell leukemia line (Jurkat) more effectively than Con A alone. We anticipate that synthetic scaffolds will offer a new means of facilitating processes that rely on cell aggregation, such as pathogen clearance and immune recognition.

Cross-linking of cell surface receptors enhances cooperativity of molecular adhesion

Cooperativity of molecular adhesion has been proposed as a mechanism for enhanced binding strength of adhesion molecules on the cell surface. Direct evidence for its mechanism, however, has been lacking until now. Atomic force microscopy (AFM) was used to measure the adhesive strength between concanavalin A (Con A) coupled to an AFM tip and Con A receptors on the surface of NIH3T3 fibroblast cells. Cross-linking of receptors with either glutaraldehyde or 3, 3'-dithio-bis(sulfosuccinimidylproprionate) (DTSSP) led to an increase in adhesion that could be attributed to enhanced cooperativity among adhesion complexes. An increase in loading rate due to greater stiffness of fixed cells also contributed to the twofold increase in binding strength. These results show that receptor cross-linking can greatly contribute to a total increase in cell adhesion by creating a shift toward cooperative binding of receptors.

A study of effects of WGA and ConA on RBC membrane receptors using a new ektacytometric method

With a new ektacytometry, we studied the relation between the microstructure of red blood cell (RBC) membrane and the rheological properties of RBCs in a shear flow field of low viscosity. The main contributions of this paper are as follows: 1. The hemorheological meanings of the orientation index (DI)or and the small deformation index (DI)d were explored. (DI)or is an overall rheological index depending on the deformability and morphology of RBCs. The better the physiological shape of RBCs is maintained, the greater the (DI)or is. (DI)d can be used to describe the lipid fluidity of RBC membrane. Such an explanation for the meaning of (DI)d has been forcefully supported by our experiments using electron spin resonance (ESR) and fluorescence polarization. 2. The influence of wheat germ agglutinin (WGA) of different concentrations on the lipid fluidity of membrane is different from that of concanavalin A (ConA). The lipid fluidity of membrane changes with WGA concentration treating RBCs and there is a maximum value for the membrane fluidity at a specific concentration of WGA. However, the deformability of membrane described by the integrate deformation index (IDI) monotonically decreased with the increase in WGA concentration treating RBCs. 3. It is concluded that the increase in the lipid fluidity of red cell membrane is not necessarily associated with the improvement of RBC deformability.

Cross-linking of concanavalin A receptors on cortical neurons induces programmed cell death

The loss of neurons by programmed cell death is a normal feature of the nervous system during development and has recently been implicated as a major mechanism of cell death in neurodegenerative diseases. In some cases, programmed cell death is induced by the activation of membrane receptors and is referred to as activation-induced programmed cell death. Activation-induced programmed cell death has been previously described in cells from the immune system, in which the activation of receptors by receptor clustering leads to programmed cell death. To determine whether activation-induced programmed cell death occurs in neurons, Concanavalin A was used to cross-link membrane receptors on cortical neurons. Concanavalin A-induced neuronal death was dose dependent and effective at concentrations previously shown to induce activation-induced programmed cell death in lymphocytes. Programmed cell death was attenuated when Concanavalin A-specific binding to neurons was blocked with methyl alpha-D-mannopyranoside. Succinyl Concanavalin A, which bound to Concanavalin A receptors but was ineffective at cross-linking them, did not induce programmed cell death. Concanavalin A-induced neuronal death exhibited many of the hallmarks associated with programmed cell death, such as membrane blebbing, nuclear condensation and margination, and internucleosomal DNA cleavage. In addition, neurons exposed to Concanavalin A displayed a rapid, robust, and persistent increase in the immediate early gene protein c-Jun. A similar increase in c-Jun precedes programmed cell death induced by beta-amyloid in neurons, and under some conditions an increase in c-Jun has been shown to be required for programmed cell death to occur in neurons. Increased expression of c-jun and other immediate early genes has also been correlated with activation-induced programmed cell death in lymphocytes. These observations suggest that Concanavalin A induces activation-induced programmed cell death in neurons via signals produced from the cross-linking of receptors on neuronal membranes. These results also raise the possibility that beta-amyloid induces programmed cell death in a similar manner, by causing the cross-linking of receptors on neuronal membranes. This mechanism may be relevant to neuronal programmed cell death that occurs during development and neurodegeneration.

Possibility of signal transduction through microfilaments below the membrane following ligand-receptor interaction

In this paper, we describe the changes of microfilament assembly and 3H-TdR incorporation in mouse ascites liver cancer cells under the action of concanavalin A (ConA) and laminin (LN). We have also studied the variation of 3H-TdR incorporation induced by destroying microfilaments with cytochalasin B (CB) following ConA and LN binding with their membrane receptors. It was found that ConA and LN interactions with their membrane receptors could induce the assembly of microfilaments below the membrane and promote DNA synthesis in these cells, but this effect was inhibited when microfilaments were destroyed by CB treatment. These results suggest that microfilaments might play a role in transferring signals from the membrane to the nucleus.

[Effect of 764-3 on ConA receptors on rat alveolar macrophages]

The changes of concanavalin A (ConA) receptors on alveolar macrophage (AM) surfaces were observed by means of ConA-horseradish peroxidase gold labelling techniques. The results were as follows: 1) The average gold particle number on normal AM surfaces was 1.985 +/- 0.097/microns, distributed uniformly; 2) On AM activated by BLMA6, in vitro, this number had increased to 3.909 +/- 0.314/microns, P < 0.001 compared with the normal group; 3) On AM preincubated with 764-3, the average gold particle number was 1.577 +/- 0.090/microns, significantly lower than that in the BLMA6 group. All results suggest that 764-3 might partially inhibit the expression of ConA-R on AM activated by BL-MA6.

Effect of erythropoietin on the interaction of concanavalin A with rat erythrocytes

Effect of Erythropoietin (Ep) on the interaction of Concanavalin A (Con A) with rat erythrocytes was studied using 125I-labelled Con A. Binding of Con A to erythrocytes was dependent on time and cell concentration. Starvation caused an elevation of the lectin binding capacity of red cells which again came down towards the normal level on Ep administration to starved rats. Binding of Con A to erythrocytes decreased linearly with increasing concentration of Ep. Specificity of binding was confirmed by inhibition studies with alpha-methyl-D-mannopyranoside (Me Man) Cells from the starved rats compared to those from normal and Ep treated animals were less prone to inhibition by this sugar analog. Positive cooperative binding of Con A to rat erythrocyte was observed at low concentration of Con A but was absent at higher lectin concentrations. Starvation caused an increase in the number of binding sites per cell which returned to normal level after Ep treatment. Under identical conditions, binding affinities were not much changed in these cells. Cells from the starved animals were more susceptible to agglutination compared to those from normal and Ep-treated rats. Microviscosity and cholesterol/phospholipid ratio of red cell membrane decreased in the starved animals which retraced its way back towards the normal level after Ep treatment.

Differential effects of glycoprotein processing inhibition on experimental metastasis formation by T24-H-ras transformed fibroblasts

Highly metastatic mouse 10T1/2 cell lines (Ciras 2, Ciras 3 and dGC2M5) which have been T24-H-ras transfected, are shown to have differential responses in metastatic properties when grown in the presence of the processing inhibitors, swainsonine, castanospermine and deoxymannojirimycin. Concanavalin A binding data indicated the inhibitors caused similar shifts in oligo-saccharide structures, resulting in more high mannose character for all cell lines. However, swainsonine inhibited the experimental metastasis of dGC2M5, but did not affect the metastatic properties of Ciras 2 and Ciras 3. Inversely, castanospermine reduced experimental metastasis of Ciras 2 and 3 and did not inhibit dGC2M5. These results show that closely related metastatic cell lines respond differently in their metastatic ability when changes occur in N-linked oligosaccharide content. This observation emphasizes the importance of oligosaccharide structure in the malignant phenotype and indicates that some caution should be used when generalizing about the effects of processing inhibitors on a complex process like metastasis.

Concanavalin A and wheat germ agglutinin binding glycoproteins associated with cell fusion and zygote differentiation in Dictyostelium discoideum: effects of calcium ions and tunicamycin on glycoprotein profiles

To determine which glycoproteins may be critical to sexual development in Dictyostelium discoideum, cell samples from different developmental stages were separated by sodium dodecyl sulfate - polyacrylamide gel electrophoresis and blotted to nitrocellulose. Concanavalin A (ConA) and wheat germ agglutinin (WGA) binding proteins were visualized on the blots using an immunochemical procedure employing peroxidase-antiperoxidase. ConA labelled at least 28 proteins, but only one band showed calcium-dependent changes in its expression. WGA bound at least 30 proteins and changes in several bands were observed that did not occur in calcium-deficient controls. Two WGA-binding glycoproteins which migrated at 200 and 166 kilodaltons (kDa), respectively, showed developmental changes associated with the time of cell fusion. One WGA-binding and one ConA-binding glycoprotein migrating at 130 and 126 kDa, respectively, appeared later during sexual development, in association with the phase of zygote differentiation. Several WGA- and ConA-binding glycoproteins decreased during sexual development, but were not affected by the absence of calcium ions. Tunicamycin (1 microgram/mL) inhibited cell fusion when added to sexual cultures prior to the appearance of the 166-kDa glycoprotein gp166. The effects of this inhibitor on development support the importance of glycoproteins to cell fusion during sexual development in D. discoideum.

Effect of different fixatives on Con A surface receptors of mouse peritoneal macrophages

The effects of glutaraldehyde, formaldehyde, or osmium tetroxide fixation on the number of labeled Con A surface receptors on mouse peritoneal macrophages were compared. Gold-labeled Con A receptors were found to be isolatedly arranged and evenly distributed on cell surfaces independent of the fixative used. Only cells preincubated with Con A and subsequently fixed by osmium tetroxide showed arrangement of labeled receptors in clusters. Significant differences were found in the number of Con A receptors per cell depending on the fixative used. The fluorescence intensity of FITC-Con A staining was detected spectrophotometrically, the characteristic X-rays of gold-labeled Con A receptors were determined by means of electron beam-induced X-ray microanalysis. The experimental results obtained both at light and electron microscopic level pointed to formaldehyde being the best fixative also for this purpose.

Age-dependent LH and FSH effect on the proliferation of women's peripheral blood lymphocytes in vitro

Pituitary gonadotropic hormones (LH and FSH) were found to induce an age-dependent proliferation of women's peripheral blood lymphocytes (PBL). Results showed that PBL of elderly women gave a higher gonadotropic response than those of younger donors and that the number of responders to the mitogenic stimulus of the hormones was always more important in older than in younger women. A negative correlation between the mitogenic effect of FSH (10(-9) g/ml) and the level of plasma concentration of some steroid hormones (17-beta-estradiol or both 17-beta-estradiol and progesterone) was observed in younger donors. It was also found that physiological concentrations of LH and FSH can either increase or decrease the Concanavalin A (Con A)-induced proliferation in vitro of PBL taken from both young or postmenopausal women. In certain elderly women (4/9) a synergistic effect of Con A and LH, giving rise to high levels of thymidine incorporation similar to those achieved by Con A-stimulated PBL of young women, was observed. The possible physiological significance of these results is discussed.

Effect of glutaraldehyde fixation on cell surface binding capacity of Candida albicans

The ability of viable and glutaraldehyde-fixed, stationary-phase yeast cells of Candida albicans to bind concanavalin A and monospecific antiserum for antigenic factor 1 was examined. Both fluorescence flow cytometric analysis and transmission electron microscopy indicated that glutaraldehyde-fixed cells bound less of the two reagents than did unfixed viable cells.

Effect of fluoride on movement of concanavalin A-acceptor molecules of human neutrophils

The effects of fluoride (F) on neutrophil protuberance formation and induced Con A acceptor molecule migration were assessed microscopically. Below 5 mM, F had little effect on acceptor migration, while it markedly inhibited formation of colchicine-induced protuberances. The anion also increased the rate at which preformed protuberances regressed. Since protuberance formation is enhanced by disassembly of microtubules, these data suggest that F promotes and/or stabilizes microtubule assembly. Microtubule assembly is favored by binding of GTP to tubulin subunits, while GDP binding favors disassembly of microtubules. Since F binds with GDP, forming a new complex that mimics GTP, the anion would be expected to enhance microtubule assembly. Over the same F concentration range, the anion failed to inhibit acceptor polarization, but did inhibit cytochalasin B-enhanced dispersion of prepolarized Con A acceptors, implying that, at low concentrations, F also affected microfilament cycling. Concentrations of F in excess of 5 mM inhibited acceptor migration as well as protuberance formation. At 20 mM, the anion abolished both events, yet at this same concentration F induced neutrophil superoxide generation and degranulation, suggesting that acceptor migration is not a prerequisite for these two neutrophil effector activities.

[Embryonic cell aggregation in the loach Misgurnus fossilis L. in vivo and in vitro. The agonist of sigma opiate receptors SKF 10,047 as a regulator of the aggregation]

SKF 10,047, known as an agonist of sigma opiate receptors of the brain, specifically interacts with the surface of embryonic cells of the loach inducing clustering of concanavalin A receptors, changing rheological properties of the membrane and causing the detachment of the cultivated cells from the glass. Both, in situ and in vitro, the rate of cellular aggregation increases together with the increase in the local density of aggregates; aggregation looses its spatial homogeneity. Therefore, there is a direct relationship between destabilization of spatially homogeneous condition at the cellular and supracellular levels.

Concanavalin A-induced redistribution of surface receptors in Acanthamoeba castellanii at different growth phases

Concanavalin A (ConA)-induced redistribution of surface receptors has been studied in Acanthamoeba castellanii at different growth phases utilizing double fluorescent techniques and transmission electron microscopy. When the amoebae were incubated with 2 micrograms and 10 micrograms tetramethylrhodamine isothiocyanate (TRITC)-ConA/ml for 4 min and 15 min at 28 degrees C the staining pattern was characterized by various numbers of scattered aggregates of fluorescent ConA. Double labeling of the amoebae showed that the fluorescent aggregates represented internalized label, and the internalization was not preceded by any aggregation of ConA receptors on the cell surface as visualized by incubating with anti-ConA serum followed by fluorescein isothiocyanate-conjugated anti-IgG. Following exposure of the amoebae to 10 micrograms TRITC-ConA/ml for 4 min and 15 min at 28 degrees C intracellular accumulation of some of the fluorescent aggregates in cap-like structures occurred at the logarithmic and postlogarithmic growth phases but not at the early stationary growth phase. Electron microscopic observation of amoebae labeled with ferritin-conjugated ConA at 28 degrees C revealed a uniform surface labeling and an intracellular accumulation of the label in vesicular and tubular structures, and occasionally in cap-like structures. Surface capping of ConA receptors in Acanthamoeba was induced by treating the amoebae with ConA and anti-ConA serum at 0 degrees C followed by incubation at 28 degrees C. The formation of surface caps in Acanthamoeba showed growth-phase dependency, too. The visualization of the surface caps at the electron microscopic level was performed by indirect staining utilizing protein A-colloidal gold.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of steroidal anesthetics on histamine release from rat mast cells stimulated by concanavalin A, compound 48/80 and A23187

1. Alphaxalone and alphadolone acetate were found to inhibit histamine release from rat mast cells induced by concanavalin A by blocking the calcium channels of the cells. 2. They also both inhibited the release induced by A23187, but only alphaxalone inhibited the release induced by compound 48/80. 3. It is concluded that the inhibitory effects of these compounds were not due to their anesthetic properties, but may have been due to their inhibition of steps of the release cascade that open calcium channels and subsequent steps.

Cyclosporin A inhibits late steps of T lymphocyte activation after transmembrane signaling

The in vitro stimulation of murine splenic T lymphocytes with concanavalin A (Con A) produced interleukin 2 (IL2). The addition of cyclosporin A (CsA) to the culture resulted in complete inhibition of IL2 production. The Con A stimulation of T lymphocytes induced the breakdown of phosphatidylinositol into inositol trisphosphate and diacylglycerol, each of which could function as the second messengers in the subsequent signal transduction pathway. CsA did not inhibit the production of inositol (poly)phosphates. Further, CsA did not affect Ca2+-calmodulin functions; a) the redistribution of various cytoskeletal proteins as well as Con A-receptor aggregation, and b) the cytosolic Ca2+-calmodulin-dependent enzyme activities. Moreover, the activity of protein kinase C, which has been accepted to be the target of diacylglycerol, was not influenced in the presence of CsA. While the above steps of signal transduction are bypassed by synergy between calcium ionophore and phorbol ester, T lymphocyte activation which was induced by such stimuli was completely inhibited by CsA. These results indicate that CsA does not influence early steps of T lymphocyte activation as bypassed by calcium ionophore and phorbol ester, but rather inhibits later step(s) subsequent to the activation of protein kinase C and Ca2+-calmodulin.

Effects of colchicine and cytochalasin B on distribution of concanavalin A receptors in isolated and cultured guinea pig epidermal cells

Regulation of the distribution of concanavalin A (Con A)/receptor complexes by the cytoskeletal contracture system was studied in guinea pig epidermal cells in suspension and culture using the fluorescence double staining method. After treatment with 100 micrograms/ml of Con A at 37 degrees C for 30 min lectin/receptor complexes were endocytosed by the less-differentiated cells in suspension and by the adherent cells in 1- and 3-day cultures that represent a growing cell fraction. The same treatment resulted in diffuse surface distribution of the complexes in the well-differentiated cells in suspension. Colchicine (10(-5) and 10(-6) M) inhibited internalization of the complexes with resultant diffuse distribution in 60% of the adherent cells in culture. Cytochalasin B (5 and 10 micrograms/ml) not only inhibited endocytosis but promoted formation of surface patchy clumps of the complexes in suspended, less-differentiated cells and cultured adherent cells. The distribution profile was not influenced by these drug treatments in the well-differentiated cells. SDS polyacrylamide gel electrophoresis and autoradiography of 125I-labelled epidermal membranes revealed several Con A-reactive polypeptides common to the cells at various differentiation steps. The progressive decrease in endocytosis and mobility of Con A/receptor complexes was suggested to occur with differentiation. In the germinative cells the distribution of lectin/receptor complexes seemed to be regulated by microfilaments and microtubules.

Target cell recognition structures in LDCC and ODCC

Cytotoxic T lymphocyte effector cells specific for a defined class I antigen can kill target cells displaying a wide range of different class I proteins in the presence of certain lectins and oxidizing agents. However, optimal lysis of the target cell (TC) still requires interaction of the CTL with the TC class I proteins. This raises the question of how the lectin or oxidizing agent alters the system in such a way that an "inappropriate" CTL-TC interaction takes place, in a class I-dependent manner. In this study we show that if papain-sensitive molecules are cleared from the TC surface and are allowed to regenerate in the presence of tunicamycin, the cells still serve as targets in direct, class I antigen-specific CTL killing, but not in LDCC or ODCC. Target cells treated in this way display N-linked carbohydrate-less class I proteins, and presumably other N-linked carbohydrate-less, papain-sensitive molecules as well. We present data showing that both types of molecules are important in nonspecific lytic reactions.

Concanavalin A receptor capping in mouse myeloma and hybridoma

Concanavalin A capping was studied in immunoglobulin-secreting hybridomas derived from fusion of mouse myeloma NSO cells with mouse spleen lymphocytes. The cells of the parental populations differed significantly in capping ability (low in myeloma cells and high in the lymphocytes). Among the hybridoma cells tested, several clones showed low capping, similar to that of the myeloma cells, some showed a good degree of capping, similar to that of the lymphocytes and other clones expressed an intermediate capping response. Capping was significantly increased in hybridoma clones of intermediate capping ability following in vivo intraperitoneal growth. A possible relationship of the variation in capping response to cell motility and to metastatic capacity is pointed out.

Inhibitory effect of chloroquine on concanavalin A internalization into cell monolayer culture

When cultured rat hepatoma cells (R-Y121B) were incubated with insulin in the presence of chloroquine at 25 degrees C, chloroquine increased both insulin binding to the cell surface and its internalization into cells. In addition, in order to elucidate whether or not the effect of chloroquine on insulin receptors is specific, concanavalin A binding to the cells was examined in the presence or absence of chloroquine, since insulin receptors have concanavalin A binding sites. When the cells were incubated with concanavalin A in the presence of chloroquine, this drug decreased concanavalin A internalization in a dose-dependent manner: The inhibitory effect of chloroquine on concanavalin A internalization was evident at a concentration as low as 0.05 mM, and increased up to 0.5 mM. The effect of chloroquine was not related to the degradation of concanavalin A incubated with cells. When the cells were incubated with concanavalin A at 4 degrees C in the presence of chloroquine even at 0.5 mM, the inhibitory effect of chloroquine was not observed. It is concluded that the behavior of insulin receptors in the presence of chloroquine is different from that of concanavalin A receptors, although insulin receptors have concanavalin A binding sites. Chloroquine apparently increases insulin binding to cells in vitro, and this is due to the effect of chloroquine on insulin-receptor recyclization to which lysosome contributes [16, 31, 32]; this drug inhibits the function of lysosome which digests insulin-receptor complexes and eventually insulin bound to its receptors is accumulated in intracellular compartments.(ABSTRACT TRUNCATED AT 250 WORDS)

Histochemical studies on Concanavalin A-binding in experimental carcinoma of the mouse submandibular gland

The lectin, Concanavalin A(Con A) has been used to localize specific sugar residues (D-glucose, D-mannose and D-fructose) in premalignant lesions and squamous-cell carcinomas induced following cryosurgery of the mouse submandibular gland. The original Con A-horseradish peroxidase (HRP) technique as well as its combination with periodate oxidation and subsequent reduction by borohydrate were used to compare the epithelial elements during submandibular gland carcinogenesis. Granules in the granular convoluted tubule cells which were weakly reactive to the Con A-HRP method were not present in the premalignant duct like structures. The epithelium of premalignant lesions, duct-like structures, multicystic lesions, and squamous-cell carcinomas were positive for the cell-surface and intercellular substances; and basement membranes and stromal fibers were also positive. The results indicated that throughout malignant transformation of the ductal segments, premalignant epithelia lost Con A-HRP-staining granules and that Con A-binding patterns in induced squamous-cell carcinomas were similar to those found in squamous-cell epithelium.

[Formation of processes during fibroblast spreading in an in vitro medium with cytochalasin B]

The spreading of normal mouse fibroblasts in a solid substrate involves extension and attachment of numerous pseudopodia resulting in the formation of lamellar cytoplasm in the cell periphery which is attached to the substrate. During the spreading of fibroblasts in the presence of cytochalasin B (CB), a system of arbor-like branched processes forms de novo, rather than lamellar cytoplasm. Unlike the normal lamellar cytoplasm, the arbor-like processes are unable to clear their surface from concanavalin A-patched receptors and do not reveal microfilament bundles in their attachment sites. The cells spreading in the presence of both CB and colcemid do not form well-organized branched structures but extend numerous unstable pseudopodia. The formation of lamellar cytoplasm can be regarded as a combination of several functionally different processes: a) rudimentary pseudopodial CB- and colcemid-resistant reactions, b) CB-sensitive lamelliation, and c) colcemid-sensitive stabilization.

Interaction of an acute phase reactant, alpha 1-acid glycoprotein (orosomucoid), with the lymphoid cell surface: a model for non-specific immune suppression

alpha 1-Acid glycoprotein (AG), a serum component elevated during acute inflammation, has been implicated in the suppression of various immunological responses. Pretreatment of lymphoid cells with AG at a concentration commonly found in patients with acute inflammation results in the inhibition of mitogen induced lymphoproliferation as well as capping of concanavalin A (Con A) receptors and surface immunoglobulin (sIg) on the lymphoid cell surface. In order to determine a potential interaction of AG with the lipid bilayer we examined the effects of purified AG on synthetic phosphatidyl choline vesicles. AG displaces 1-anilino-8-naphthalene sulphonate (ANS), an anionic surface probe from these vesicles yet is unable to perturb the binding of N-phenyl-1-naphthalamine (NPN), a hydrophobic probe of the membrane interior. The non-immunosuppressive asialo-derivative of AG is incapable of displacing ANS from the vesicles. The interaction of AG with the membrane may partially involve electrostatic forces mediated by sialic acid and/or steric hindrance of receptor mobility. The results suggest that AG has the capacity to perturb the lymphoid cell surface and interfere with events required for lymphocyte proliferation.

The effects of gold sodium thiomalate on the binding and internalization of concanavalin A in human mononuclear phagocytes

The effects of gold sodium thiomalate (GST) on the binding and internalization of concanavalin A (Con A) in human mononuclear phagocytes (M phi) were investigated in vitro. First, the binding and internalization of Con A were examined quantitatively using 3H-Con A. The prolonged incubation with GST induced a prominent inhibition of 3H-Con A internalization in M phi. The inhibition was increased in parallel with both increasing concentrations of GST and increasing time intervals of the incubation with GST. On the other hand, GST failed to significantly affect the binding of 3H-Con A to the M phi surface receptor. Second, the binding and internalization of Con A were examined qualitatively by fluorescein isothiocyanate-conjugated Con A (FITC-Con A). After incubation with GST for 72 h, the internalization of FITC-Con A was prominently impaired in vacuolated M phi. A significant inhibition of FITC-Con A internalization was not observed in either GST-treated nonvacuolated M phi or non-GST-treated M phi. Thus the inhibition of FITC-Con A internalization in GST-treated vacuolated M phi seemed to account for the inhibition of 3H-Con A internalization in all the GST-treated M phi populations. The binding of FITC-Con A to the cell surface receptor and the clustering of FITC-Con A receptor complexes were not detectably changed in any of the M phi populations. These results indicated that GST alters the initial step in the activation of M phi by Con A, namely the internalization of this mitogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of cell-associated concanavalin A by methyl alpha-D-mannopyranoside reveals three binding states of concanavalin-A receptors on mouse fibroblasts

Based on the partial reversibility of concanavalin A binding by saturating concentrations of methyl alpha-D-mannopyranoside (MeManp) three states of cellular association could be characterized: type I, most rapidly established and most tightly bound, not released by MeManp at 0 degrees C or at 37 degrees C; type II, most loosely bound, released by MeManp at 0 degrees C, therefore not critically dependent on the temperature at which the release reaction is performed; type III, intermediate strength of binding, released by MeManp only at 37 degrees C, thus reflecting the temperature-sensitive nature of these cell complexes. A similar temperature dependence was found for cell-bound concanavalin A when it was displaced by an excess of the same lectin. The types of binding are seen irrespective of the temperature at which the cellular association was established. About 10% of the concanavalin A molecules bind to receptor structures in a saturable way and represent the type I association. Type I association is clearly distinct from types II and III. Type II seems to be the precursor of type III. Most of the type II associations can be converted into type III associations since ConA-cell complexes originally sensitive to the action of MeManp at low temperature gradually do become resistant after prolonged association at the same temperature. The temperature dependence in binding to cells was, however, not related to receptor mobility since glutaraldehyde-treated cells had most of the release properties that were observed in untreated cells and which did not markedly differ between 3T3 cells and their SV40-transformed counterparts. In contrast to cellular binding, dissociation of concanavalin A from Sephadex beads by saturating concentrations of MeManp was complete irrespective of temperature.

Alterations in the structure of the oligosaccharide of vesicular stomatitis virus G protein by swainsonine

Swainsonine, an inhibitor of glycoprotein processing, inhibits the formation of the normal oligosaccharide chain of the G protein of vesicular stomatitis virus. Thus, when vesicular stomatitis virus was grown in baby hamster kidney cells in the presence of swainsonine (15 to 500 ng/ml) and labeled with [2-(3)H]mannose, the oligosaccharide portion of the G protein was completely susceptible to the action of endoglucosaminidase H. However, the normal viral glycoprotein is not susceptible to this enzyme. Various enzymatic treatments and methylation studies of the mannose-labeled oligosaccharides suggest that swainsonine causes the formation of a hybrid-type oligosaccharide having an oligomannosyl core (Man(5)GlcNAc(2)-Asn) characteristic of neutral oligosaccharides plus the branch structure (NeuNAc-Gal-GlcNAc) characteristic of the complex oligosaccharides. A structure for this hybrid oligosaccharide is proposed. Swainsonine had no effect on the incorporation of [(14)C]leucine into viral proteins, nor did it change the number of PFU produced in these cultures. It did, however, slightly decrease the incorporation of [(3)H]glucosamine and increase the incorporation of [(3)H]mannose. Vesicular stomatitis virus raised in the presence of swainsonine bound much more tightly to columns of concanavalin A-Sepharose than did control virus. Swainsonine had to be added within the first 4 or 5 h of virus infection to be effective. Thus, when 100 ng of the alkaloid per ml was added at any time within the first 3 h of infection, essentially all of the glycoprotein was susceptible to digestion by endoglucosaminidase H. However, when swainsonine was added 4 h after the start of infection, 30% of the glycopeptides became resistant to endoglucosaminidase H; at 5 h, 70% were resistant. The effect of swainsonine was reversible since removal of the alkaloid allowed the cells to form the normal complex glycoproteins. However, the time of removal was critical in terms of oligosaccharide structure.

Sendai virus envelopes can mediate Epstein-Barr virus binding to and penetration into Epstein-Barr virus receptor-negative cells

Epstein-Barr virus (EBV) receptor-negative cells were treated with UV-inactivated Sendai virus (SV) or with reconstituted SV envelopes having a low hemolytic activity and then assayed for EBV binding or for susceptibility to EBV infection. EBV binding was assessed by using both unlabeled and fluoresceinated EBV preparations. It was found that SV or SV envelope treatment renders these cells able to bind EBV. Various experiments were performed to clarify the mechanism of this SV-induced binding. The EBV receptor-negative 1301 cells were treated with SV either at 0 degrees C or at both 0 and 37 degrees C successively and then examined for EBV binding at 0 degrees C. It was thus found that when SV treatment was performed exclusively at 0 degrees C, the target cells showed higher fluorescence intensity after their incubation with fluoresceinated EBV. In addition, Clostridium perfringens neuraminidase treatment of 1301 cells did not induce any EBV binding to these cells. These data indicate that EBV binding is not due to the disturbance of the cell membrane by SV envelope fusion or to the uncovering of EBV binding sites on the cells after the enzymatic action of SV neuraminidase. Moreover, bound EBV was partly eluted from SV-treated 1301 cells at 37 degrees C, and the treatment of EBV with C. perfringens neuraminidase inhibited its SV-mediated binding. These data indicate that EBV binds to the hemagglutinin-neuraminidase of SV on the target cell surface and that a fraction of the bound EBV becomes irreversibly associated with the SV-treated cell membrane. Our data also show that EBV can penetrate into 1301 cells which have incorporated SV envelopes into their membrane, as demonstrated by the induction of the EBV-determined nuclear antigen by B95-8 EBV in SV envelope-treated 1301 cells.

Tissue-specificity of reactivity to concanavalin-A of human cells in culture

Concanavalin-A (Con-A) reactivity was studied to identify the tissue-specificity of cells established from various normal human tissues. Cells were treated with Con-A-labelled human red blood cells (C-RBC). C-RBC was not absorbed on the cells derived from the bone marrow, skin and liver. Lung-derived fibroblast cells showed weak C-RBC adsorption. Kidney-derived cells showed epithelial morphology and easily adsorbed C-RBC. These suggest that a large number of Con-A receptors exists on the membrane surface of kidney cells.

Concanavalin A-mediated agglutination and distribution of concanavalin A-binding sites in Acanthamoeba following treatment with colchicine and cytochalasin B

Incubation of Acanthamoeba castellanii (Neff strain) with FITC-ConA (15 micrograms/ml) resulted in the appearance of patches of fluorescence on the amoebae within 2 min of incubation. These patches disappeared following treatment of the amoebae with alpha-MeMan. Pretreatment of the amoebae with colchicine or cytochalasin B or with colchicine and cytochalasin B in combination did not significantly alter the distribution pattern of fluorescence in the amoebae. 2,4-Dinitrophenol and incubation at 4 degrees C on the other hand decreased the degree of patching of the amoebae. Pretreatment with 2,4-dinitrophenol and incubation at 4 degrees C also decreased the ConA-mediated agglutination of the amoebae. No effect on the ConA-mediated agglutination was, however, observed following pretreatment of the amoebae with colchicine and cytochalasin B neither alone nor in combination. Our results indicate that ConA-mediated agglutination and long-range ConA-receptor mobility in the Acanthamoeba are not under the control of structures sensitive to cytochalasin B or colchicine.

[Ability to redistribute surface receptors in transplantable cell lines]

The ability of cultured lymphoid, erythroid and fibroblastic cells for ligand-induced redistribution of their surface receptors proved to be lower than that of lymphocytes. The process of surface receptors redistribution can be inhibited by low temperature and sodium azide in all the cells under study. Pretreatment with trypsin increased the ability for redistribution of surface receptors in some types of cultured cells, but had no such effect on lymphocytes. These differences between lymphocytes and cultured cells seem to be due to differences in organization of the surface and contractile systems of the respective cells.

Formation of total, active and stable E-rosettes by human lymphocytes stimulated with con A derivatives

Peripheral blood lymphocytes from healthy human volunteers where incubated for 48 hr with 10 micrograms/ml of native Con A or its dimeric derivatives, succinyl- and acetyl-Con A. The percentage of total-active and stable E-rosettes were determined before and after incubation. There were no differences among the three forms of the lectin. Stable E-rosettes exhibited the most dramatic effects from Con A stimulation. They increased from approximately 2% in control cultures to 20-25% in stimulated cultures. Treatment with the Con A inhibitor alpha-Methyl-D-mannoside after Con A stimulation did not affect the rosette formation. Our results suggest that redistribution of membrane receptors on stimulated lymphocytes is not responsible for increased E-rosette formation after Con A stimulation since dimeric forms of Con A are not able to induce membrane receptor redistribution.

Adsorption of concanavalin A on human platelets

A physiological cell surface adsorption system approach is investigated on human platelets utilizing mathematical modeling. Monodispersed washed platelets are freshly collected in an isotonic buffer as a suspension utilizing a gel filtration technique. Concanavalin A is used as a glycoprotein receptor adsorbate in the adsorption studies. Three mathematical models are proposed based on simple chemical equilibrium reactions between adsorbate and cell surface receptors in an effort to explain concanavalin A - platelet surface glycoprotein interaction. Model I assumes that all receptors are undergoing simultaneous surface reactions with the adsorbate and without correlation. Model II reflects a strong correlation between the receptors, when only one receptor is active and the second receptor(s) is nothing but the combination of first receptor-adsorbate complex. Model III assumes the presence of multiple receptors on the cell surface. Only when a specific fraction of the total number of one receptor have reacted, will the other receptor(s) initiate reaction with the adsorbate. The results suggest the existence of at least three major glycoprotein receptors interacting with the lectin, and having different equilibrium constants as indicated in the adsorption isotherm. Model III seems to support best the experimental data of concanavalin A interaction with platelet surface glycoproteins.

Interactions of lectins with CHO cell surface membranes. II. Differential effects of local anesthetics on endocytosis of Con A and WGA binding sites

Using fibroblastic CHO cells, we have examined 1) the internalization and redistribution of surface binding sites for the lectins Concanavalin A and wheat germ agglutinin and 2) the sensitivity of these processes to putative inhibitors of cytoskeletal activity. Following initial exposure to fluorescein conjugated Con A (CAF) or WGA (WGAF) at 4 degrees C, kinetic analysis of internalization and intracellular aggregation of lectin at 37 degrees C indicated more rapid aggregate formation in the case of WGA than in the case of Con A. Treatment with tertiary amine local anesthetics (tetracaine, dibucaine, and xylocaine) or with a lysosomatrophic amine, m-dansyl cadaverine, blocked internalization of Con A but not of WGA. Similar differential effects on redistribution of Con A and WGA were not however observed with the antimicrotubule agents colchicine and nocodazole. Simultaneous treatment of cells with WGAF and with rhodamine labeled Con A (CAR) resulted in the accumulation of both labels in a central perinuclear aggregate; a similar experiment in the presence of local anesthetic resulted in a diffuse peripheral distribution of CAR and a central aggregate of WGAF. These results suggest 1) CHO cells possess at least two distinct pathways for lectin internalization and redistribution, which can be discriminated in terms of drug sensitivity; 2) CHO cells can sort out and independently internalize different populations of lectin binding sites; and 3) different pathways may be a manifestation of biochemically distinct linkages between cytoskeletal elements and various groups of surface glycoproteins. Present findings concur with our previous results concerning the mutual independence of the surface binding sites for Con A and WGA (Emerson and Juliano, 1982).

Receptor-mediated regulation of mitogenic response

We have investigated the requirements of mitogenic response of mouse spleen cells for free and cell-bound concanavalin A (Con A) and inhibition of the response by egg lecithin. We also studied 125I-Con A binding with the mouse cells at different times after stimulation with the lectin. Our results suggested that mitogenic response to Con A by mouse spleen cells may be regulated by two receptor-mediated mechanisms acting in concert. Mitogenic response was inhibited during the first 2 hr following stimulation with Con A by removing free Con A from culture medium. But after 4 hr, the response became independent of free Con A and, concomitantly, Con A binding by mouse cells increased by about 2-3 fold. It was further shown that the increase in Con A binding depends on prior reaction of the cells with the lectin but it does not, on de novo protein synthesis. Treatment of mouse cells with glutaraldehyde may also increase Con A binding. These results suggested that the initial Con A binding with mouse cells may not be sufficient to initiate mitogenic response. It may however mobilize those Con A receptors which have remained hitherto cryptic but occupancy of which by Con A may be essential for triggering of mitogenic response. The second mechanism affects mitogenic response at a time after receptor mobilization and before cells are committed to proliferation. The nature of this mechanism remains obscure but it requires Con A binding and is sensitive to inhibition by the membrane active substance, egg lecithin.

Effects of beta interferon on concanavalin A binding and size of HeLa cells

Treatment of HeLa-S3 cells with 640 u/ml of human beta interferon (HuIFN-beta) in suspension culture increases the cell volume and the heterogeneity of the population with respect to cell size, as measured by Coulter electronic volume analysis. Based on such analysis, the cell surface area is increased 11% by 24 h, and 42% by 48 h after beginning of interferon treatment. Binding of [125I] Concanavalin A (measured at 22 degrees C) is increased 75% by 24 h, and 120% by 48 h on a per-cell basis. It follows that interferon treatment for 24 h causes a 58% increase in the abundance of functional Con A receptor sites per unit area of cell surface. The further increase in Con A binding after treatment of cells with interferon for 48 h can be attributed to increased surface area of cells.

Cholera toxin B-subunit protects mammalian cells from ricin and abrin toxicity

The glycoproteins ricin and abrin intoxicate cells by inhibiting protein synthesis. Pretreatment of HeLa cells with cholera toxin partially protects them from ricin and abrin activity. The involvement in this phenomenon of the various effects of cholera toxin, namely, redistribution of membrane receptors elicited from protomer B and increasing cyclic AMP concentrations induced by protomer A, were studied. Substances able to enhance cyclic AMP concentrations do not affect ricin and abrin activity, while protomer B alone protects cells. In addition, the effects of several lectins on ricin or abrin toxicity were examined. Almost complete prevention of ricin or abrin activity was obtained using concanavalin A (Con A) and wheat germ agglutinin (WGA). Conversely, neither succinyl Con A nor Ulex europeus agglutinin (UEA) affected the cellular response. Both protomer B of cholera toxin and Con A did not alter the binding of ricin or abrin; they seem to protect cells by altering membrane structure.

Use of fluorescent probes to monitor propranolol effects on the murine splenic lymphocyte

Recent studies indicate that propranolol suppresses the normal murine lymphocyte mitogen dose-response(1) and that propranolol has a high affinity for the beta-adrenergic binding site on the murine lymphocyte(2). Since concentrations which suppress the lymphocyte mitogen dose-response are much greater than the Kd for the binding site, it may be suggested that the suppression of the mitogen dose-response is a result of nonspecific effects of propranolol. Three fluorescent probes (1,6-diphenyl-1,3,5-hexatriene (DPH), fluorescein conjugated concanavalin A (F-Con A), and 3,3'-dithio-diisopropyl-oxacarbocyanine iodide (diS-C3-(5)) were used to investigate possible mechanisms of the nonspecific effects of propranolol on the murine splenic lymphocyte. This report presents data which suggests a possible relationship between propranolol concentrations that alter lipid membrane dynamics, as monitored by the fluorescence polarization of DPH, and suppression of the mitogen dose-response in short term cell cultures as effected by propranolol. Also reported are effects of propranolol on the relative mobility of surface membrane lectin receptors as monitored by the fluorescence polarization of F-Con A, effects of propranolol on the transmembrane potential as monitored by fluorescence emission of diS-C3-(5), and the propranolol effect on fluorescence polarization temperature-dependence of DPH and F-Con A. Studies of the effects of sotalol, alprenolol, and metoprolol are included and used for the comparison of different drug effects.

[Redistribution of concanavalin A receptors on the thrombocyte surface]

Using the indirect immunofluorescence method, it has been shown for the first time that concanavalin A receptors can undergo a redistribution over the surface of platelets spread on the substrate. The distribution of receptors in the intact cells is diffuse and random. Con A receptors, cross-linked by their ligand, are removed from the surface of the lamellar cytoplasm of living substrate-spread platelets. These receptors move into the central part of cell surface. This phenomenon is similar to capping or clearing of lamellar cytoplasm of big nucleated cells. Cytochalasin B (10 mcg/ml) does not prevent the formation of patches of receptors but inhibits the clearing of the lamellar cytoplasm of spread platelets. This result suggests that microfilaments may be involved in the redistribution of receptors.

Inhibitory effect of cytochalasin H on cell reaggregation of the fresh water sponge, Ephydatia meyeni Carter

Cytochalasin H (CH) has been shown to inhibit the reaggregation of dissociated cells of a fresh water sponge. The effect is dose-dependent and reversible. Even after 24 h of CH treatment, the cells show the formation of pseudopodia suggesting that the effect of CH may not be due to arrested cell motility. Exogenously added alpha-D-glucosamine, a precursor of complex carbohydrates, brings about reaggregation of CH-treated cells. Fluorescent Con A binding, both patching and capping, is shown by untreated as well as CH-treated cells. It is likely that CH, like cytochalasin B, may interfere with the production, release or binding of carbohydrate-containing macromolecules important in cell aggregation.

Maximizing differences in the concanavalin A-induced blastogenic responses of lymphocytes from breast cancer patients and controls by the use of alpha-methyl-D-mannoside

In an attempt to magnify differences in the immune responses of potentially immunosuppressed cancer patients and normal controls, an assessment was made on the effects of the competitive inhibitor alpha-methyl-D-mannoside on the concanavalin A (Con A)-induced blastogenic responses of lymphocytes from each of these populations. Lymphocytes from breast cancer patients with metastatic disease were significantly deficient in their capability to undergo blast transformation regardless of whether the monosaccharide inhibitor was added to the assay cultures. In contrast, lymphocytes from breast cancer patients who did not display metastatic disease were capable of normal blastogenic responses to Con A. The addition of alpha-methyl-D-mannoside to lymphocyte cultures caused a significantly greater inhibition of the blastogenic responses of these patients' cells as compared to cells of normal controls. Thus the monosaccharide seems to serve as a useful reagent for optimizing differences between lymphocyte blastogenic responses of normal donors and those of immunodepressed donors. The results suggest that lymphocytes from breast cancer patients without clinically evident metastases possess some modification of their cell membrane. One possibility discussed was that the number or distribution of receptors for Con A on the membrane of lymphocytes of these patients is deficient.

Translational mobility of concanavalin A receptors in normal and neoplastic glial cells

The dynamics of cell-associated Concanavalin A (Con A) in astrocytes of the newborn rat (RNA), the rat glioma (AC), and the human glioblastoma (GB) were studied in vitro by fluorescence and electron microscopy. Con A receptors on the cell surface were seen usually as a continuous thin layer, and Con A accumulations in fluorescence microscopy were actually Con A receptors on complicatedly infolded cell membrane and collection of Con A pinosomes. No capping occurred in the three types of glial cells. The translational movement of Con A receptors on the cell surface was rapid in the AC, slow in the RNA, and intermediate in the GB, and partly associated with Con A internalization. Con A pinosomes were more numerous in the RNA compared with those in the AC and the GB. Colchicine accelerated the translational mobility of surface Con A receptors more markedly in the AC and the GB than in the RNA. The translational movement Con A receptors, when treated with cytochalasin B, was retarded in the RNA and the GB and rather accelerated in the AC. Con A pinosomes were decreased in the three types of glial cells by treatment with colchicine or cytochalasin B.

Synthesis and application of cleavable photoactivable heterobifunctional reagents

Three different cleavable photoactivable heterobifunctional reagents have been synthesized and characterized by proton NMR, 13C NMR, mass spectroscopy, infrared spectroscopy, and thin-layer chromatography. They are the N-hydroxysuccinimide ester of 3-[(4-azidophenyl)dithio]-propionic acid, methyl 3-[(4-azidophenyl)dithio]propionimidate, and N-[(4-azidophenyl)thio]phthalimide. Concanavalin A was coupled with one of the reagents, the N-hydroxysuccinimide ester of 3-[(4-azidophenyl)dithio]propionic acid, and radioiodinated. The [125I]lectin derivative and [125I]lectin showed similar specific binding to the receptors on the human erythrocyte membrane. Upon photolysis, subunits of the [125I]lectin derivative were cross-linked to produce dimer, trimer, and tetramer. These cross-linked complexes were readily cleaved by reducing the disulfide bond of the reagent.

A study on concanavalin A binding to human erythrocytes

Interactions of concanavalin A with human erythrocytes were studied using 125I-labelled concanavalin A and a centrifugal technique with dibutyl phthalate which permitted complete separation of bound and free concanavalin A. Binding of 125I-labelled concanavalin A to human erythrocytes was dependent on cell concentration, pH and temperature. Specificity of binding was confirmed by inhibition and dissociation studies with sugars and native concanavalin A. Positive cooperative binding of concanavalin A to human erythrocytes was observed at low concanavalin A concentrations (less than I microgram/ml) in both buffers studied. Positive cooperativity at higher concanavalin A concentrations (more than 100 microgram/ml) was seen in Tris-Hepes buffer but not in phosphate-buffered saline. Consistent with this cooperative effect was the observation that although dissociation of 125I-labelled concanavalin A from the erythrocytes was complete in the presence of 1 mg/ml of the native lectin, release was inhibited by low concentrations (1 microgram/ml). A comparison of concanavalin A binding with hemagglutination studies suggests that the amount of concanavalin A bound determines the rate of erythrocyte agglutination and the size of the aggregates formed.