Immunochemical determination of ganglioside GM2, by inhibition of complement-dependent liposome lysis

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.

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.

Antibody response of rabbits to nerve ending gangliosides. Analysis of antibody specificity by liposome lysis and lysis inhibition assays

Rabbits were immunized with nerve ending fraction prepared from guinea pig brain. Serum antibodies to total gangliosides were followed by enzyme-linked immunosorbent assay; their titers were highest at 2 to 3 weeks after immunization and some rabbits showed a response to reinjections. Specific reactivities of the antibodies against each molecular species of gangliosides were analyzed by liposome lysis assay and liposome lysis inhibition assay. Antibody responses were detected against GM1, GD1b, GM3 and GM2, but not against GD1a and GT1b. Natural and immune antibodies to the asialo glycolipids and to galactosylceramide were also observed.

Immunochemical determination of Forssman and blood group A-active glycolipids in human gastric mucosa by inhibition assay of liposome lysis

A simple liposome immunoassay, liposome immune-lysis inhibition (LILI) assay, is described for quantitative determination of individual glycolipid antigens. Liposomes containing fluorogenic marker, 4-methylumbelliferyl phosphate, were prepared from sphingomyelin, cholesterol, dicetylphosphate and standard glycolipid. Release of trapped markers from these liposomes by antibody and complement (liposome lysis) was inhibited by preincubating the antibody with test glycolipid incorporated into inhibitor liposomes. Based on the competitive inhibition, it was possible to quantitate each glycolipid antigen in less than picomolar amounts. The sensitivity and specificity of the assay were examined with purified glycolipid standards. LILI assay has been applied for the determination of Forssman glycolipid and blood group A-active glycolipid in human gastric mucosa and cancer tissues.

Dynamics of antibody- and lectin-mediated endocytosis of hapten-containing liposomes by murine macrophages

The uptake by murine macrophages of liposomes, exhibiting one of a variety of haptenic groups on their surfaces, was greatly enhanced by the addition of an intact antibody or a lectin specific for the incorporated hapten. The uptake of untreated liposomes was slow and linear over long periods, whereas upon addition of the antibody or lectin, over 30-fold increase in the maximal rate of uptake was observed. The process reached a plateau after 90-120 min. The interaction of the antibody- or lectin-treated liposome with the macrophages apparently resulted in an active endocytosis of soluble fluorescent, intraliposomal marker had a granular intracellular pattern in treated cells. The uptake was sensitive to azide and the liposome constituents could not be detected at the cell surface. The size of the liposomes as well as the state of stimulation of the macrophages (thioglycollate stimulated vs. normal) did not seem to have a major effect on the phagocytic process. The time required to reach the plateau in uptake was independent of liposome composition or antibody concentration and is, apparently, an intrinsic property of the cells. The implication of this phenomenon on the dynamics of the relevant macrophage receptors is discussed.

A new assay for lytic anti-galactocerebroside (GC) antibodies employing 56Rubidium release from GC-labelled liposomes

This assay is a quick and sensitive method for determination of antibodies to galactocerebroside (GC). The use of antibody-plus-complement radioisotope release from GC-bearing liposomes allows numerous samples to be handled in semi-automated fashion. By substituting alternative gangliosides or cerebrosides, the technique may be simply modified for assay of antibodies to other substances.

A simple radioimmunoassay to determine binding of antibodies to lipid antigens

A solid-phase radioimmunoassay to determine the binding of antibodies to lipid antigens is described. Polyvinyl chloride microtiter plates were coated with lipid antigens by placing in each well 25--100 microliters of solutions of the antigens in ethanol and evaporation of the solvent. The wells were than washed with 0.3% gelatine solution to remove loosely bound antigens and to saturate the plastic with an unrelevant protein to prevent unspecific binding of antibodies to the plates. About one-third of [3H] phosphatidylcholine adsorbed in this way (out of 1 nmole) was firmly attached to the plastic and was not washed away during a standard assay. The rest, loosely bound lipid, was washed away in the first 5 washings before the primary antibodies were applied. The technique is rapid and convenient and is as sensitive as a conventional solid-phase radioimmunoassay with protein antigens. It requires minute amounts of antigen. Less than 10(-12) moles of lipid antigen can be detected by this technique.

Anti-ganglioside antibodies in multiple sclerosis

Serological activity against several purified brain gangliosides has been demonstrated in sera of a proportion of multiple sclerosis patients, but not in normal individuals. The activity was determined by the capacity of the sera to bring about complement-dependent lysis of liposomes containing the respective ganglioside in their lipid bilayer. An apparent correlation is indicated between the severity of the disease and the extent of liposome lysis. Cerebrospinal fluid of the patients did not induce lysis, probably due to low antibody concentration.

Radioimmunoassay of glycosphingolipids: application for the detection of forssman glycolipid in tissue extracts and cell membranes

Development of a radioimmunoassay for detecting glycosphingolipids has been difficult, primarily because of transfer of radiolabeled glycolipid antigen to the unlabeled antigen pool. This difficulty has been overcome by the use of a radiolabeled glycolipid-polymer. Thus, an assay system has been developed for measuring picomolar quantities of Forssman hapten glycolipid. This assay is based on competition for rabbit anti-Forssman antibodies between Forssman glycolipid and a radiolabeled Forssman polyacrylic hydrazide polymer. Antigen-antibody complexes are removed quickly and efficiently by binding to formalin-fixed Staphylococcus aureus and subsequent centrifugation. One nanogram of Forssman glycolipid can be readily detected both in plasma membrane preparations and in purified glycolipid fractions. The isoantigenic expression of Forssman glycolipid in human gastrointestinal tissues has been reported previously (Hakomori et al., 1977). Using the radioimmunoassay, the Forssman status of several additional cases has been determined quantitatively.