Antiglycolipid antibodies in normal and pathologic human sera and synovial fluids

Antigen-specific enhancement of natural human IgG antibodies to phosphatidylcholine, phosphatidylglycerol, phosphatidylinositol-4-phosphate, cholesterol, and lipid A by a liposomal vaccine containing lipid A

Natural IgG antibodies (NA) to lipids are ubiquitously distributed in sera of healthy humans and are believed to serve beneficial functions. Although NA to lipids generally exhibit germ line or near germ line binding specificities, the antibodies commonly increase transiently in the acute phases of most, if not all, infectious diseases and may serve as a first line of defense. In order to determine whether similar anti-lipid antibodies can be induced by a vaccine in humans, we examined stored sera obtained from volunteers who had previously received a candidate vaccine to Plasmodium falciparum. The vaccine had consisted of liposomes that contained both the recombinant protein antigen and also contained monophosphoryl lipid A (MPLA) as an adjuvant. All of the pre-immune sera contained NA to one or more of the liposomal lipids in the vaccine: dimyristol phosphatidylcholine (DMPC), dimyristoyl phosphatidylglycerol (DMPG), cholesterol, and MPLA. After initial immunization, followed by a boost, increased levels of IgG antibodies to all of the liposomal lipids, especially DMPG and MPLA, were observed by ELISA. Antibodies to phosphatidylinositol-4-phosphate (PIP) above the normal pre-immune NA to PIP were also observed. Although PIP was not present in the immunizing liposomes, based on the adsorption of anti-PIP antibodies by DMPG the anti-PIP antibodies were thought to represent cross-reacting anti-DMPG antibodies. The immune response was apparently antigen-specific in that NA to unrelated lipids, other than PIP, that were not present in the liposomes, galactosyl ceramide and ganglioside GM1, were not increased by the immunization. We conclude that antibodies to DMPC, DMPG, PIP, cholesterol, and MPLA can be induced in humans by immunization with liposomes containing MPLA.

Central nervous system involvement in systemic lupus erythematosus: cerebral imaging and serological profile in patients with and without overt neuropsychiatric manifestations

The aim of this study was to evaluate morphological and functional abnormalities by cerebral imaging in a series of systemic lupus erythematosus (SLE) patients with and without overt central nervous system (CNS) manifestations, and to detect possible relationships with clinical parameters and a large panel of autoantibodies, including those reactive against neurotypic and gliotypic antigens. 68 patients with SLE were investigated in a cross-sectional study which included clinical evaluation of symptoms, cerebral magnetic resonance imaging (MRI) and brain single photon emission tomography (SPECT) analysis, electroencephalography (EEG), and serological tests for antibodies directed against nuclear, cytoplasmic neuronal and glial cell-related antigens. The results of this study showed: (1) a significant positive association of (a) anti-glial fibrillary acidic protein (GFAP) serum antibodies with neuropsychiatric (NP) manifestations and (b) anti-serin proteinase 3 (anti-PR3/c-ANCA) serum antibodies with pathological cerebral SPECT; (2) the presence of significantly higher values of (a) SLICC organ damage index in patients with abnormal MRI and (b) SLAM activity index in patients with abnormal SPECT; and (3) the association of (a) abnormal MRI with nonactive NP manifestations and (b) combined abnormality of brain SPECT and MRI with the occurrence of overall overt NP manifestations and with those of the organic/major type. Neuropsychiatric manifestations, namely those of the organic/major type, appeared to be significantly associated to the presence of a serum antibody against GFAP, a gliotypic antigen. There was also evidence of an association between SPECT abnormality and the presence of anti-PR3 (c-ANCA). Furthermore, brain imaging by MRI and SPECT applied to SLE patients appears to express CNS involvement significantly related to specific categories of NP manifestations. The abnormalities detected by the two tests seem to be preferentially associated with different activity phases of the NP disorder or of the lupus disease.

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.

Complement-dependent phagocytosis of liposomes

In this article we describe an in vitro model for complement-dependent phagocytosis of liposomes. We have previously reported that complement-opsonized liposomes are avidly ingested by murine peritoneal or bone marrow-derived cultured macrophages. However, when the liposomes contained certain lipids, including phosphatidylinositol, ganglioside GM1, and sulfogalactosyl ceramide, that have been identified as causing prolonged circulation time in vivo, complement-dependent phagocytosis of the liposomes was greatly suppressed. We identify certain additional factors associated with suppressed complement-dependent phagocytosis, including, liposomal negative charge and liposomal prostaglandin E2 or thromboxane B2. Possible mechanisms responsible for suppression of complement dependent phagocytosis are suggested. We propose that suppression of complement-dependent phagocytosis could be a contributing factor in the promotion of increased circulation time of 'stealth' liposomes and that complement opsonization probably plays a role in vivo in removing liposomes from the circulation.

Aberrant expression of GM1 on lymph node cells of MRL/Mp-lpr/lpr mice: influences on the autoreactivities of anti-asialo GM1 antibodies

Although changes in surface carbohydrate expression of abnormally expanded MRL/Mp-lpr/lpr (MRL/lpr) lymph node (LN) cells have previously been described, the composition and function of glycolipids present on these cells as well as the spectrum of specificity of anti-carbohydrate antibodies reactive with these cells remains obscure. Analysis of antibodies to a panel of 22 carbohydrate structures using a liposome immune lysis assay (LILA) showed that, except for anti-asialo GM2 (GA2) antibodies, marked reduction of antiglycolipid antibody levels was observed in sera from 4-mo-old MRL/lpr mice compared with these from MRL/Mp(-)+/+ (MRL/+) mice. Absorption experiments revealed that both anti-asialo GM1 (GA1) and globoside antibodies had binding capacity to MRL/lpr LN cells. To elucidate the glycolipid profiles of MRL/lpr LN cells, glycolipids were extracted from LN cells of both MRL/lpr and MRL/+ mice and analysed. A 30-fold elevation of GM1 was found in MRL/lpr LN cells compared with MRL/+ LN cells. From the results of LILA using GA1/GM1 mixed liposomes, aberrantly expressed GM1 inhibited the classical complement pathway but did not interfere with the binding of anti-GA1 antibodies to liposomal GA1. These findings suggest that a drastic GM1 increase on MRL/lpr LN cells would inhibit the action of anti-GA1 antibodies and complement on the cell surface. This may explain the escape of these cells from an activated self directed immune response.

Autoantibodies against Forssman glycolipids in Graves' disease and Hashimoto's thyroiditis

Sera from patients with Graves' disease and Hashimoto's thyroiditis have been shown to react with the Forssman glycolipid antigen (Gb5) using the techniques of high performance thin-layer chromatography (HPTLC) immunostaining and ELISA. Human monoclonal antibodies (MoAbs) have been prepared by fusion of human myeloma with peripheral lymphocytes from patients with Graves' disease. A MoAb, TRMo-4, reacted strongly and specifically with Gb5. These results suggest that anti-Forssman antibody may be involved in the pathogenesis of these autoimmune diseases. The detection of anti-Forssman glycolipid antibody may provide a useful means for clinical diagnosis and therapy.

Naturally occurring human IgG antibodies to intracellular and cytoskeletal components of human platelets

Immunoblotting of platelets that have been subjected to SDS-PAGE has revealed that sera from normal individuals contain IgG which binds to many platelet components. This binding was seen with autologous and heterologous platelets using serum of males and of nulliparous females who had not received blood transfusions. Although binding patterns of different sera were not identical, almost all sera caused IgG binding to platelet components of 87-90 kD, 140 kD (identified as vinculin) and 220-240 kD (tentatively identified as talin and actin-binding protein). Purified IgG showed the same binding pattern as whole serum and F(ab')2 fragments retained their ability to bind to many components. The titre of IgG binding in serum was 1:50-1600 while that of alloantibodies to the PlA1 antigen was 1:3200. IgG binding components were not secreted when platelets were stimulated and were rarely associated with isolated membranes, but were located either in platelet cytoplasm or cytoskeletons. IgG binding was decreased by absorbing sera with lysed platelets or isolated cytoskeletons, but only slightly with intact platelets. Microaffinity purification of IgG which formed a major band on immunoblots showed that it was antibody with specificity for vinculin or its degradation products. These findings suggest that normal sera contain naturally occurring IgG antibodies with specificity for intracellular platelet antigens and that in some cases their titre approaches that of antibodies of pathological significance.

Interaction between human natural anti-alpha-galactosyl immunoglobulin G and bacteria of the human flora

Anti-alpha-galactosyl immunoglobulin G (anti-Gal) is a natural antibody present in unusually high amounts in human sera. It constitutes as much as 1% of circulating immunoglobulin G in humans and displays a distinct specificity for the carbohydrate epitope galactosyl alpha(1----3) galactosyl (Gal alpha 1----3Gal). Recently, it has been suggested by various investigators that anti-Gal may be related to some autoimmune phenomena, since marked elevation of its titer was found in sera of patients with autoimmune thyroid disorders, rheumatoid arthritis, glomerulonephritis, and Chagas' disease. In view of the ubiquitous presence of anti-Gal in high titers in humans, throughout life, we hypothesized that, analogous with synthesis of anti-blood group antibodies against bacterial antigens, bacteria within normal intestinal flora may provide constant antigenic stimulation for the synthesis of anti-Gal. This hypothesis would imply that anti-Gal may bind to a variety of bacterial strains of human flora. In the present study, the interaction between affinity chromatography-purified anti-Gal and various bacterial strains was studied. By the use of a direct immunostaining assay and an enzyme-linked immunosorbent assay, anti-Gal was found to interact with a variety of Escherichia coli, Klebsiella, and Salmonella strains, some of which were isolates from normal stool. Furthermore, the anti-Gal-binding sites in some strains were found to be present on the carbohydrate portion of bacterial lipopolysaccharides. It is thus suggested that Gal alpha 1----3Gal epitopes in the outer membranes of normal flora enterobacteria may provide a continuous source for antigenic stimulation. Since there is no immune tolerance to the Gal alpha 1----3Gal carbohydrate structure in humans, anti-Gal seems to be constantly produced in response to these enterobacteria. In addition, bacteria which express Gal alpha----3Gal epitopes and which may adhere to various cells mediated binding of anti-Gal to human cell lines. These findings raise the possibility that anti-Gal may damage normal human tissues via inflammatory processes facilitated by bacterial Gal alpha 1----3Gal epitopes.

Lipooligosaccharides (LOS) of Neisseria gonorrhoeae and Neisseria meningitidis have components that are immunochemically similar to precursors of human blood group antigens. Carbohydrate sequence specificity of the mouse monoclonal antibodies that recognize crossreacting antigens on LOS and human erythrocytes

We have used mouse mAbs, 3F11 and 06B4, that are specific for highly conserved epitopes of Neisseria gonorrhoeae lipooligosaccharides (LOS) to identify immunochemically similar structures on human erythrocytes. mAb 3F11 agglutinated erythrocytes from all randomly selected adult humans, while mAb 06B4 agglutinated only 80% of the same specimens. The antibodies had an activity with erythrocytes similar to human cold agglutinins in that agglutination occurred at 4 degrees C and decreased with increasing incubation temperature. Human infant erythrocytes were agglutinated less well, but enzymatic treatment of either infant or adult cells resulted in an increase in expression of the 3F11- and 06B4-defined epitopes. Both antibodies bound to a series of neutral glycosphingolipids from human erythrocytes and neutrophils that have a type 2 (Gal beta 1----4GlcNAc) or N-acetyllactosamine structure. Neither antibody bound to glycosphingolipids from human meconium, which have a type 1 (Gal beta 1----3GlcNAc) structure. The antibodies were unable to bind to N-acetyl-lactosamine glycosphingolipids with a nonreducing terminal sialic acid or a Gala1----3Gal disaccharide. Antibody binding also was blocked by the presence of fucose linked to the penultimate glucosamine residue of N-acetyllactosamine glycosphingolipids. Although both antibodies bound to linear and branched-chain N-acetyllactosamine glycosphingolipids, 3F11 had a higher affinity for branched structures than did 06B4. The activity of 3F11 with human adult and infant treated and untreated erythrocytes with N-acetyllactosamine glycosphingolipids, and with LOS was very similar, if not identical, in specificity to 1B2, an mAb prepared from mice inoculated with a linear N-acetyllactosamine glycosphingolipid.

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.

Pancreatic islet cell surface glycoproteins containing Gal beta 1-4GlcNAc-R identified by a cytotoxic monoclonal autoantibody

To investigate the autoimmune pathogenesis of spontaneously occurring diabetes mellitus in BB rats, spleen cells of newly diagnosed diabetic BB rats were fused with mouse myeloma cells. Hybridoma supernatants were screened for antibodies by indirect immunofluorescence and by 51Cr-release assays using the RINm5F rat insulinoma cell line. One clone, E5C2, produced an IgM kappa antibody that was cytotoxic for RINm5F cells, but not for other rat cell lines nor for primary rat islet cells. However, treatment of primary rat islet cells with neuraminidase exposed surface antigens and rendered the cells susceptible to complement-mediated lysis by antibody E5C2. Using immunostaining of glycolipids separated by thin-layer chromatography, hapten inhibition assays with defined carbohydrates, and Western blots, the antigens recognized by E5C2 on RINm5F cells were identified as glycoproteins with molecular weights of 60,000 and 68,000. The antibody recognizes a carbohydrate antigen containing the sequence Gal beta 1-4GlcNAc-R, which on RINm5F cells is predominantly hidden by covalently bound sialic acid. These studies raise the possibility that hidden antigenic determinants on islet cells exposed by a variety of means may be the target of autoimmune attack.

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.

Inhibitory effects of gangliosides on immune reactions of antibodies to neutral glycolipids in liposomes

Specific immune damage to liposomes containing Forssman or globoside glycolipid was inhibited when the liposomes also contained ganglioside. The activity of a human monoclonal Waldenström macroglobulin antibody to Forssman glycolipid was inhibited by each of three gangliosides tested, GM3, GD1a and GD1b. Inhibition of the monoclonal antibody was dependent on the amount of ganglioside in the liposomes, and was diminished by reducing the relative amount of ganglioside. Inhibition also correlated positively with the number of ganglioside sialic acid groups, with inhibition by GT1b greater than GD1a greater than GM3. Naturally occurring human antibodies to globoside glycolipid were detected in 18% (9 out of 50) of normal human sera tested. Immune damage to liposomes induced by each of the three highest-reacting human anti-globoside sera was blocked by liposomal GM3. We conclude that gangliosides can strongly influence immune damage to membranes induced by antibody interactions with adjacent neutral glycolipids.