A simple method to measure anti-glycolipid antibody by using complement-mediated immune lysis of fluorescent dye-trapped liposomes

Vesicle-Based Assays to Study Membrane Interactions of Amyloid Peptides

The growing interest in membrane interactions of amyloidogenic peptides and proteins emanates from the realization that lipid bilayers and membranes play central roles in the toxicity and pathological pathways of amyloid diseases. This chapter presents experimental schemes designed to study membrane interactions and membrane-induced fibrillation of amyloid peptides.

Membrane interactions of ionic liquids: possible determinants for biological activity and toxicity

Ionic liquids (ILs) are a class of diverse organic salts with relatively low melting points (below 100°C) which have attracted considerable interest as a promising "green" substitute for organic solvents. The broad solvation properties of ILs and their high solubility in water, however, present health risks, in particular since it was shown that many ILs exhibit cytotoxic properties. In this context, interactions of ILs with the cellular membrane are believed to constitute a primary culprit for toxicity. We present a comprehensive biophysical and microscopy study of membrane interactions of a series of ILs having different side-chain compositions and lengths, and cationic head-group structures and orientations. The experimental data reveal that the ILs studied exhibit distinct mechanisms of membrane binding, insertion, and disruption which could be correlated with their biological activities. The results indicate, in particular, that both the side chain composition and particularly the head-groups of ILs constitute determinants for membrane activity and consequent cell toxicity. This work suggests that tuning membrane interactions of ILs should be an important factor for designing future compounds with benign environmental impact.

Development of Liposome Immune Lysis Assay for the Herbicide Atrazine

A homogeneous complement-mediated liposome immune lysis assay (LILA) was developed for determination of the herbicide atrazine. To dispose the antigen on the surface of lipid bilayer the atrazine was conjugated to a dimirystoylphosphatidylethanolamine (DMPE) carrier. Calcein was compared with sulforhodamine 101 as a fluorophore label for entrapping into the antigen-sensitized liposomes. The liposomes were incubated with rabbit anti-atrazine antibodies in the presence of guinea pig complement. Formation of the antigen-antibody complexes on the liposomal surface initiated the lytic action of the complement. As free competing atrazine inhibited the lytic reaction, the amount of calcein released was inversely proportional to the atrazine content in the probe. Concentration and kinetic dependences of the immunoassay were characterized to reach its maximal sensitivity. The developed assay allows detecting atrazine in concentrations up to 0.13 ng mL(-1) in the sample (0.04 ng mL(-1) in the final reaction mixture). The named sensitivity is two orders higher than those for the microplate enzyme-linked immunosorbent assay (ELISA) with the same antibodies which allows us to recommend LILA for environmental monitoring.

A kinetics approach to the characterization of an IgM specific for the glycolipid asialo-GM1

The unique features of protein recognition of membrane-anchored glycolipids were investigated by surface plasmon resonance (SPR) monitoring of antibody interactions with glycolipids contained in liposomes. Several positive hybridomas belonging to the IgM and IgG classes were identified when tested for binding to the glycosphingolipid asialo-GM1 (Gal beta1-3GalNAcl beta1-4Gal beta1-4Glc beta1-1-Ceramide). Preliminary screening by enzyme immunoassay and thin layer chromatography (TLC) followed by immunostaining indicated that only those of the IgM type showed specificity for this glycosphingolipid. One of the IgMs, H2G10, was purified and further characterized using a SPR technique that involved antibody binding to liposomal asialo-GM1. This method generated kinetic and affinity constants for the interaction and confirmed the specificity of H2G10 for the terminal galactose of asialo-GM1. Interestingly, inhibition of antibody binding to asialo-GM1 liposomes by the asialo-GM1 tetrasaccharide reduced the total amount of bound antibody but increased the affinity of the antigen-antibody interaction due to an inverse relationship between tetrasaccharide concentration and the H2G10 dissociation rate constant. We believe that this effect is due to the selective inhibition of lower valency binding by the tetrasaccharide which, in turn, promotes higher avidity antibody-carbohydrate interactions. The observation that slower dissociation rate constants were also observed at high antigen to antibody ratios supports this interpretation. These results highlight the insight that kinetic data can provide in efforts to promote and inhibit high avidity interactions such as those involving proteins and carbohydrates.

Transdermal immunisation with an integral membrane component, gap junction protein, by means of ultradeformable drug carriers, transfersomes

Molecules greater than 500 Da normally do not cross the skin. This prevents epicutaneous delivery of the high molecular weight therapeutics as well as non-invasive transcutaneous immunisation. Extremely deformable vesicles prepared by the judicious combination of several materials provide a solution to this problem: the resulting agent carriers, transfersomes, are the only tested colloidal system that can transport even large macromolecules spontaneously through the skin in immunologically active form. Gap junction proteins (GJP) incorporated into transfersomes and applied to the intact skin surface thus give rise to specific antibody titres marginally higher than those elicited by subcutaneous injections of GJP in transfersomes, mixed lipid micelles or liposomes. The latter two carrier systems give no significant biological response after epicutaneous administration. Transcutaneous protein delivery by means of transfersomes also appears to increase the relative concentration of anti-GJP IgA in the serum.

Liposomes and immunoassays

Various aspects of the application of liposomes as a label in immunoassays are reviewed. Methods for the preparation of liposomes, from the basic film method to the more advanced dehydration-rehydration method, are discussed. Furthermore, the markers used in liposome labels, as well as the methods to conjugate liposomes to antigens or antibodies, are summarized. Liposome immunoassays are applied as homogeneous or heterogeneous assays. Homogeneous assays often rely on the lytic activity of complement on antibody-associated liposomes. Another group of homogeneous assays utilizes the inhibitory action of antibodies on the activity of conjugates of mellitin (a bee venom protein) with a hapten. Free mellitin conjugates are able to lyse liposomes effectively. Heterogeneous liposome immunoassays, performed either competitively or non-competitively, resemble more closely standard enzyme linked immunosorbent assays, with the enzyme being replaced by a liposome label. Washing steps are used to separate antigen-specifically bound liposomes from unbound liposomes. All bound liposomes are lysed with a detergent, giving an instantaneous amplification. Flow-injection liposome immunoassays and liposome immunosensors are also described as examples of other possible immunoassay formats.

Antibody dependent, complement mediated liver uptake of liposomes containing GM1

PURPOSE

We have previously reported that GM1 exhibits an opposite effect on regulating liposome circulation time in mice and rats (Liu et al. Pharm. Res. Vol. 12:508-512 (1995)). Inclusion of GM1 into liposomes significantly prolongs liposome circulation time in mice, while it dramatically decrease the blood half life and increases liver uptake of liposomes in rats. The purpose of this study was to elucidate the mechanism that underlies this phenomenon.

METHODS

Single-pass liver perfusion in vitro and complement mediated liposome lysis assay was used.

RESULTS

Serum appeared to play an important role in determining the liver uptake of GM1 liposomes. Specifically, rat serum enhanced the uptake of GM1-containing liposomes by the perfused liver. Such activity was also found in human and bovine serum, but not in mouse serum. Taking human serum as an example, we demonstrated that such serum activity can be blocked by EDTA and EGTA/Mg2+. Antibodies against human IgM and the third component of complement system (C3) also inhibited serum activity.

CONCLUSIONS

The presence of naturally occurring anti-GM1 antibodies in rats, through the activation of the classic pathway of complement system, is likely the cause of rapid blood clearance of GM1-liposomes. The third component of complement is likely to serve as the opsonin that is directly involved in mediating liposome clearance.

Production of human monoclonal antibodies to i blood group by EBV-induced transformation: possible presence of a new glycolipid in cord red cell membranes and human hematopoietic cell lines

To study the differentiation-associated glycolipid two anti-i mAb producers, GL-1 and GL-2, were established from the combination of EBV-induced transformation of normal PBL and immune lysis of fluorescent dye-trapped liposome-containing bovine i-active glycolipid. The mAb GL-1 reacted with both sialosylparagloboside and pentahexosyl ceramide and the bovine i-active glycolipid whereas mAb GL-2 reacted only with the bovine i-active glycolipid in LILA. Both mAbs cold-agglutinate human cord red cells but not adult red cells. However, unexpectedly, the majority of the reactivity of these mAbs in human cord red cells on TLC was not identical to the i-active glycolipid. The GL-1 antigenic substance is considered to be a glycolipid distinct from the i-active glycolipid because the immunoreactivity was canceled with endoglycoceramidase which cleaves a linkage between the oligosaccharide and ceramide. Based on complement cytolysis with the mAb, 15 hematopoietic cell lines and normal peripheral lymphocytes were screened for susceptibility to the mAbs. A Burkitt lymphoma cell line, Ramos, was most sensitive among those tested, and BJA-B, Daudi, Namalwa in the B cell lines, TALL-1, Jurkatt in the T-cell lines and HL-60 in the non-lymphoid cell lines were sensitive whereas normal lymphocytes or other 8 cell lines were not. An immunoreactive spot with the same Rf with cord red cells was also detected in sensitive cell lines. The possible presence of a new glycolipid antigen determined from the mAb and related to the differentiation of hematopoietic cells was speculated.

The use of streptavidin-biotin interaction for preparation of reagents for complement-dependent liposome immunoassay of proteins: detection of latrotoxin

We have developed liposome sensitization by a protein, latrotoxin (LT), using immobilization of biotinylated LT via streptavidin with biotinylated phosphatidylethanolamine contained in liposomes. The use of such liposomes in the complement-dependent homogeneous liposome immune lysis assay (LILA) has allowed us to detect in the test sample as little as 2 micrograms/ml of polyclonal and 50-100 ng/ml of monoclonal IgG and IgM antibodies to LT. LT concentration in solution was determined by inhibition of immune lysis by free LT. The sensitivity of the LT assay varied from 1 x 10(-9) to 5-50 x 10(-9) M when antiserum (polyclonal antibodies) and monoclonal antibodies to LT were correspondingly used. The results show that a streptavidin-biotin spacer can be used to immobilize protein antigens on liposomes for a subsequent application in LILA. The suggested technique greatly simplifies the sensitization procedure and extends the applicability of the LILA.

Liposome immune lysis assay (LILA) for gelonin

A complement-mediated liposome immune lysis assay using entrapped calcein was developed for a plant toxin gelonin. Gelonin was covalently coupled to DPPE, and then adsorbed on to the surface of liposomes. Such antigen-bearing liposomes when incubated with anti-gelonin antibody in the presence of guinea pig complement undergo lysis. The detection range is from 3 ng to 60 ng. The method was used to monitor isolation of gelonin by affinity chromatography. It was observed that a minor peak in addition to the major one comes with gelonin, shared common epitopes/epitope with gelonin in immunological reaction. This was further confirmed by SDS-gel electrophoresis indicating the former being an isoform of gelonin. A comparative study of the immunocross-reactivity of ricin and ricin A chain with anti-gelonin antibody was carried out. It was found that while ricin A chain cross-reacted extensively with gelonin antibody and intact ricin elicited little or no cross-reactivity. It is suggested that the present LILA may be employed for the detection and quantitation of ricin A chain by this LILA method.

Studies on osmotic stability of liposomes prepared with bacterial membrane lipids by carboxyfluorescein release

The authors measured the osmotic stability of liposomes prepared with membrane lipids of bacteria, using the osmotic-shock release of entrapped carboxyfluorescein as an indicator. The sub-second physical changes of liposomes suspended in a solution of low osmotic pressure were examined by stopped flow spectrophotometry. The entrapped carboxyfluorescein was released when the liposomes burst on inflow of excess water. Liposomes prepared with the lipids of a stable Staphylococcus aureus L-form strain were more resistant to low osmotic pressure than those prepared from the wild strain of S. aureus, and liposomes prepared from Mycoplasma orale were even more resistant. Cardiolipin enhanced the lipid membrane stability in S. aureus and cholesterol in M. orale. The stability of lipid membranes to low osmotic pressure could be precisely determined by the present method.

Fluorescence quenching measurements of the membrane bound lipid haptens with different length spacers

Dansyl lipid haptens with three different length (short, intermediate and long) spacers have been incorporated into DMPC or DPPC liposomes. Anti-DNS-IgG bound most efficiently to these liposomes containing lipid haptens with an intermediate length spacer, although the binding efficiency became more increased when liposomes were made of a mixture of phospholipid (DMPC or DPPC) and cholesterol. To explain these results we have measured the accessibility of dansyl lipid haptens in liposomal membranes by the fluorescence quenching method. It was found that the dansyl haptens located on the surfaces of DMPC (or DPPC) membranes and fluorescence quenchers (iodide ions) possessed almost similar accessibility for the dansyl haptens with different length spacers. However, in the DMPC (or DPPC) membranes with 50% cholesterol, a part of the dansyl haptens became buried into the interior of the liposomal membranes depending on the length of the spacer and another part removed into the aqueous solution with greater affinity for antibody. These results were explained well by our recent model for antibody binding to the membrane-bound lipid haptens.

Assay of complement activity in human serum using large unilamellar liposomes

Liposomes incorporating 2,4,6-trinitrophenyl-aminocaproyl-dipalmitoylphosphatidylethanolamine (TNP-cap-DPPE) as a membrane hapten can be lysed by human complement in the presence of anti-TNP antibody. Liposomes were composed of L-alpha-dimyristoylphosphatidylcholine, cholesterol, TNP-cap-DPPE and dicetylphosphate at a molar ratio of 1:1:0.005:0.02. Large unilamellar liposomes were prepared by reverse-phase evaporation with an entrapped marker, carboxyfluorescein, which is self-quenching in liposomes at high concentrations such as 0.2 M. When the marker is released by complement action, a strong fluorescence is produced. The amount of marker released from liposomes is able to quantify complement activity of both the classical and alternative pathways. CL50 is the complement activity obtained by lysis of 50% of the liposomes. The number of CL50 units in sera obtained with liposomes correlates well with those obtained using the hemolytic complement test CH50 (r = 0.98). The advantages of this method include stability of reagents, accuracy, simplicity and speed. In addition, it is well suited for developing an automated system. This method is a useful substitute for the hemolytic assay for determination of human complement activity.

Homogeneous immunoassay for alpha 2 plasmin inhibitor (alpha 2PI) and alpha 2PI-plasmin complex. Application of a sandwich liposome immune lysis assay (LILA) technique

The measurement of the alpha 2 plasmin inhibitor (alpha 2PI) and alpha 2PI-plasmin complex is important for a complete understanding of fibrinolytic conditions. Using monoclonal antibodies against alpha 2PI, a sandwich liposome immune lysis assay (LILA) has been used for the quantitation of alpha 2PI and the alpha 2PI-plasmin complex. In the assay system for the measurement of alpha 2PI, anti-alpha 2PI monoclonal antibodies were covalently coupled to liposomes and specific lysis of liposomes was observed when the liposomes were incubated with the alpha 2PI antigen, TNP haptenized second monoclonal antibody against alpha 2PI and complement activating rabbit anti-TNP antibody. The same liposomes and rabbit anti-plasminogen antibody could be used for the homogeneous determination of the alpha 2PI-plasmin complex. The former assay suggests that monoclonal antibodies lacking complement-activating ability can be used in the sandwich LILA technique. The second application suggests that the LILA technique is capable of measuring heterocomplexes. These assays, which involve the same analytical system, are simple, fast and highly sensitive. They are potentially useful in determining the fibrinolytic status of patients.

Hydrophilic fluorescein derivatives: useful reagents for liposome immunolytic assays

Hydrophilic derivatives of fluorescein containing hydroxyalkyl substituents were synthesized and encapsulated within liposomes. The fluorophores showed significantly more retention with time than did fluorescein, carboxyfluorescein, or calcein. Unlike calcein, the fluorophores are minimally susceptible to fluorescence quenching by Co2+. The utility of these compounds as immunodiagnostic reagents was demonstrated by encapsulating 5(6)-carboxyfluorescein trismethylolamide in haptenized liposomes which were used in an immunoassay for digoxin.

Prevention of nonspecific lysis in liposomal and erythrocyte immunoassay systems by small lipid vesicles and erythrocyte ghosts

Large unilamellar liposomes prepared by the reverse-phase evaporation method (REVs) were made immunoreactive by incorporating dinitrophenylaminocaproyl-phosphatidylethanolamine (DNP-Cap-PE) or 8-(3-carboxypropyl)-theophylline-dipalmitoylphosphatidylethanolamine (Th-DPPE) into the phospholipid bilayer. Specific lysis in the presence of anti-DNP-BSA and goat anti-theophylline serum respectively, was induced by adding guinea pig serum as source for complement to these liposomes. However, specific lysis was found to be compromised by high levels of nonspecific lysis as monitored by the release of the fluorescent aqueous-space marker 6-carboxyfluorescein. Nonspecific lysis could be prevented without affecting specific lysis by pretreatment of complement or incubation of the reaction mixture with small unilamellar liposomes (SUVs). SUVs of various lipid compositions produced the desired effect; however, when the fraction of negative charge in the SUVs was increased to 30 mol%, specific lysis was inhibited as well. In a similar assay system consisting of hemolysin-sensitized sheep red blood cells it was also found that nonspecific lysis could be inhibited by addition of erythrocyte ghosts to the incubation medium, although specific lysis was somewhat depressed. However, SUVs or REVs of a composition similar to sheep erythrocytes were ineffective indicating a more selective nature of complement-mediated immunoreaction with erythrocyte membranes than with synthetic bilayer membranes.

Homogeneous liposome lysis assay for determination of anti-streptolysin O antibody titer in serum

We developed a liposome lysis assay for determining anti-streptolysin O antibodies (ASO) in human sera involving the use of carboxyfluorescein-entrapped multilamellar liposomes. This assay system was based on the inhibition of streptolysin O-induced liposome lysis by ASO. Briefly, after incubation of a given amount of streptolysin O with ASO for 30 min at 37 degrees C, carboxyfluorescein-entrapped liposomes composed of egg yolk phosphatidylcholine and cholesterol in a molar ratio of 1:1 were added to the mixture to determine the residual streptolysin O activity. Liposome lysis, detected as carboxyfluorescein release from the liposomes, was inversely proportional to the ASO titer. The results of within-run and between-run precision studies indicated that the liposome lysis assay is accurate and gives reproducible data. Bilirubin, hemoglobin, and triglycerides did not interfere with the liposome lysis assay. The ASO titers of 100 patient sera, evaluated by our new method and the Rantz-Randall method, showed good correlation.

Membrane-damaging action of staphylococcal alpha-toxin on phospholipid-cholesterol liposomes

The mechanism of membrane damage by staphylococcal alpha-toxin was studied using carboxyfluorescein (internal marker)-loaded multilamellar liposomes prepared from various phospholipids and cholesterol. Liposomes composed of phosphatidylcholine or sphingomyelin and cholesterol bound alpha-toxin and released carboxyfluorescein in a dose dependent manner, when they were exposed to alpha-toxin of concentrations higher than 1 or 8 micrograms/ml, respectively. In contrast, the other liposomes composed of phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol or phosphatidylinositol plus cholesterol were not susceptible to the toxin even at high concentrations up to 870 micrograms/ml. The insensitive liposomes containing either phosphatidylserine or phosphatidylglycerol were made sensitive to alpha-toxin by inserting phosphatidylcholine into the liposomal membranes. In addition, phosphorylcholine inhibited the toxin-induced marker release from liposomes. These results indicated that the choline-containing phospholipids are required for the interaction between alpha-toxin and liposomal membranes. Susceptibility of liposomes containing phosphatidylcholine or sphingomyelin increased with the increase in cholesterol contents of the liposomes. Based on these results, we propose that the choline-containing phospholipids are possible membrane components or structures responsible for the toxin-membrane interaction, which leads to damage of membranes. Furthermore, cholesterol may facilitate the interaction between alpha-toxin and membrane as a structural component of the membrane.

Liposome immune lysis assay (LILA). Application of sandwich method to determine a serum protein component with antibody-bearing liposomes

A complement-dependent liposome immune lysis assay (LILA) using carboxyfluorescein (CF)-entrapped liposomes bearing antibody was developed to measure C-reactive protein (CRP) antigen as a model of protein antigens in human sera. Goat anti-CRP antibody was covalently coupled to liposomes, and a specific lysis of the liposomes could be observed when the liposomes were incubated with both rabbit anti-CRP antibody (secondary antibody) and CRP antigen in sera in the presence of guinea pig complement. In this assay system, so-called sandwich assay, CRP (a multivalent antigen) bound to the liposomes bearing anti-CRP antibody and subsequently secondary antibody, which activated complement efficiently. The amount of CF released by a complement-dependent liposome immune lysis was proportional to CRP concentrations. This sandwich assay was simple, fast, highly sensitive, and covered the ranges 10-300 ng of CRP/ml in a homogeneous mode, that is, one where no separation step was employed. The results correlated well with those obtained by single radial immunodiffusion and enzyme immunoassay. This assay system would be applicable to the measurement of other protein antigens.

Antiglycolipid antibodies in normal and pathologic human sera and synovial fluids

Antiglycolipid antibodies were measured in normal and pathologic sera and synovial fluids by means of a modified microplate method of complement-mediated immune lysis of fluorescent dye-trapped liposomes. All sera of normal subjects had antibodies against globopentaosylceramide (IV3 GalNAcGbOse4Cer), ganglioside GM1, gangliotriaosylceramide, gangliotetraosylceramide, and galactosylneolactotetraosylceramide antigens. Most sera of normal subjects had antibodies against lactotriaosylceramide, N-glycolylneuraminosyl-neolactotetraosylceramide (NeuGcnLcOse4Cer), GM3 ganglioside with N-glycolylneuraminic acid (NeuGcGM3) and GD1a antigens. Differences of titers against IV3GalNAcGbOse4Cer, neolactotetraosylceramide, NeuGcGM3 and NeuGcnLcOse4Cer antigens were observed between sera of normal subjects and pathologic sera from cases of leukemias, lymphomas, several autoimmune diseases and liver diseases.

Acute joint inflammation in mice after systemic injection of the cell wall, its peptidoglycan, and chemically defined peptidoglycan subunits from various bacteria

The systemic injection of an aqueous suspension of cell wall or its peptidoglycan (PG)-rich sonicate derived from group A streptococcus and Lactobacillus casei induced acute joint lesions in BALB/c, DBA/1J, (BALB/c X DBA/1J)F1, and C3H/He mouse strains, but not in C57BL/6, DBA/2, and AKR strains. Cell walls and their enzymatically degraded PG fragments from other bacteria as well as the synthetic disaccharide dipeptide and Lactobacillus plantarum cell wall-derived disaccharide tripeptide produced similar acute inflammation in susceptible BALB/c mice. Acute swelling and erythema of the ankles and wrists were observed as early as 3 h, reached maximum severity by day 2, and generally subsided by days 4 to 6 after injection. Histological studies showed synovial proliferation, marked infiltration of many mononuclear cells and a few polymorphonuclear leukocytes in the soft tissues, and extensive deposition of fibrinous exudate in the joint space. Antibody response was detectable against the PG fraction. However, anti-PG antibody does not seem to be responsible for the pathogenesis of this disease. On the other hand, experiments on decomplementation by cobra venom factor suggest that complement components are involved in the early phase of this arthritic model.

Liposome immune lysis assay (LILA): a simple method to measure anti-protein antibody using protein antigen-bearing liposomes

A new simple immunoassay technique using immune lysis of liposomes was developed to measure antibody against protein antigens. Multilamellar liposomes were composed of dipalmitoylphosphatidylcholine, cholesterol and phosphatidylethanolamine substituted with the hetero-bifunctional cross-linking reagent N-hydroxysuccinimidyl 3-(2-pyridyldithio)propionate (SPDP). The protein antigen (human IgG) was coupled to these liposomes after treatment with SPDP and mild reduction. As a release marker, carboxyfluorescein (CF) was entrapped in the liposomes. The CF release was specific to anti-human IgG antibody and depended on the presence of complement. This technique could detect 10(-15) mol of anti-human IgG antibody or human IgG. The liposomes were stable over 8 months at 4 degrees C under nitrogen gas.

Biological activities of analogues of lipid A based chemically on the revised structural model. Comparison of mediator-inducing, immunomodulating and endotoxic activities

Lipid A analogues were chemically synthesized based on the model structure recently revised, and biological activities of the analogues were tested. The analogue, (beta-1,6)-linked glucosamine disaccharide carrying ester-bound 3-hydroxytetradecanoic acids at 3 and 3' position of reducing and nonreducing glucosamine in addition to amide-bound 3-hydroxytetradecanoic acids and glycosidic-linked and ester-linked phosphate groups, showed much stronger activities for mediator inducing and immunomodulating as well as endotoxic activities than those exhibited by the previously synthesized analogues based on the old model. Among the activities tested, induction of interferon and tumor necrosis factor as well as mitogenicity, adjuvanticity and pyrogenicity were, however, not expressed so strongly as natural lipid A used as controls. In contrast, the analogue exhibited comparable activities to those of control lipid A in the test of lethal toxicity to mice and gelating activity of Limulus amebocyte lysate. Other synthetic analogues carrying a phosphate group showed comparable, slightly stronger or weaker activities depending on the test, but nonphosphorylated analogue exhibited no apparent or only very weak activities.

A new method of evaluating complement mediated lysis of liposomes

Immune lysis of liposomes has been utilized in immunoassays for detection of specific antibodies. Membrane immunoassays which have sensitivities comparable with those of radioimmunoassays are easy and rapid to perform. Information obtained so far has been limited by the fact that the method is based on empirical relationships. The present paper describes a simple theoretical model for analysing membrane immunoassay data. According to the model, relative dissociation constants for the antibody-antigen reaction and relative concentrations of high affinity antibodies for different antisera may be determined. Furthermore, the analysis yields the percentage of antibody bound to antigen under certain conditions. The method is also useful in the search for optimum experimental conditions in membrane immunoassay measurements.

Serological specificity of the liposome lysis test for measurement of anti-ganglioside antibodies. A comparison with hemagglutination inhibition

A simple and reliable complement-dependent liposome lysis test for the detection of anti-ganglioside antibodies is described. For sera raised in rabbits against the monosialoganglioside NG-GM3, the sensitivity and specificity of antibody detection was compared with that of the HRBC hemagglutination-inhibition test: the liposome lysis test appears more sensitive. A difference in antigen presentation was also demonstrated.

Differing reactivities of human and guinea-pig complement on haptenized liposomes via the alternative pathway

Several haptens coupled to dipalmitoylphosphatidylethanolamine (DPPE) were inserted into the liposome membrane with a base composition of an equimolecular mixture of dimyristoylphosphatidylcholine (DMPC) and cholesterol (Chol). Haptens used were trinitrophenyl (TNP)-DPPE, TNP-aminocaproyl (TNP-Cap)-DPPE, dinitrophenyl (DNP)-DPPE, DNP-aminocaproyl (DNP-Cap)-DPPE, fluoresceinthiocarbamyl (Fl)-DPPE, azobenzenarsonate-tyrosyl (ABA-Tyr)-DPPE, dansyl (DNS)-DPPE, dabsyl (DABS)-DPPE, dithiopyridyl (DTP)-DPPE and maleimidobenzoyl (MB)-DPPE. Reactivity of those haptenized liposomes with complement via the alternative pathway was assessed by release of trapped fluorescent marker from the liposomes following incubation with dilutions of guinea-pig and human sera in a diluent containing MgCl2 and ethyleneglycol-bis(beta-aminoethyl ether)N,N'-tetraacetate (EGTA). In the diluent (Mg-EGTA-GVB), complement activation via the alternative pathway proceeds while that via the classical pathway is inhibited. Fl-liposomes were found to be extremely sensitive to guinea-pig complement, being lysed by guinea pig serum dilutions of up to 1:76 in Mg-EGTA-GVB. Guinea-pig serum could lyse TNP-Cap-liposomes, DNP-Cap-liposomes, TNP-liposomes, DTP-liposomes, MB-liposomes, DNP-liposomes and ABA-Tyr-liposomes, with the reactivity of the liposomes decreasing in this order. However, the only haptenized liposomes sensitive to human serum in Mg-EGTA-GVB were DTP- and MB-liposomes; the other liposomes including Fl-liposomes being unreactive via the alternative pathway in reaction with human complement.

A quantitative analysis of cell surface glycosphingolipid with a fluorescence activated cell sorter

The fluorescence activated cell sorter (FACS) was used with an indirect membrane immunofluorescence technique to detect antibody against the Forssman antigen, a glycosphingolipid. Sheep erythrocytes, which contain Forssman antigen as a major membrane glycosphingolipid, were used as the target antigen. Detection of the anti-Forssman antibody on the sheep erythrocytes was done with specific fluorescein-conjugated second antibody and analyzed on a FACS. Compared to other available methods, analysis with the FACS was simple, sensitive, reproducible and quantitative. More than 250 pg of antibody could be detected. In addition, as little as 1 ng of Forssman antigen could be estimated by a binding inhibition experiment.

Forssman antibody levels in sera of cancer patients

By means of SRBC lysis in agarose gel and Forssman (F) liposome lysis assay, serum levels of F antibodies were determined in various cancer patients. F antibody titers of the patient's sera were shown to be lower than that of normal controls. Following radical surgery, F antibody titers were elevated significantly in most of the patients with advanced gastric, colorectal and lung cancer. Similar tends of anti-A antibody titers were observed in group O and B patients with advanced cancer.