An α-Gal-containing neoglycoprotein-based vaccine partially protects against murine cutaneous leishmaniasis caused by Leishmania major

Background

Protozoan parasites from the genus Leishmania cause broad clinical manifestations known as leishmaniases, which affect millions of people worldwide. Cutaneous leishmaniasis (CL), caused by L. major, is one the most common forms of the disease in the Old World. There is no preventive or therapeutic human vaccine available for L. major CL, and existing drug treatments are expensive, have toxic side effects, and resistant parasite strains have been reported. Hence, further therapeutic interventions against the disease are necessary. Terminal, non-reducing, and linear α-galactopyranosyl (α-Gal) epitopes are abundantly found on the plasma membrane glycolipids of L. major known as glycoinositolphospholipids. The absence of these α-Gal epitopes in human cells makes these glycans highly immunogenic and thus potential targets for vaccine development against CL.

Methodology/Principal findings

Here, we evaluated three neoglycoproteins (NGPs), containing synthetic α-Gal epitopes covalently attached to bovine serum albumin (BSA), as vaccine candidates against L. major, using α1,3-galactosyltransferase-knockout (α1,3GalT-KO) mice. These transgenic mice, similarly to humans, do not express nonreducing, linear α-Gal epitopes in their cells and are, therefore, capable of producing high levels of anti-α-Gal antibodies. We observed that Galα(1,6)Galβ-BSA (NGP5B), but not Galα(1,4)Galβ-BSA (NGP12B) or Galα(1,3)Galα-BSA (NGP17B), was able to significantly reduce the size of footpad lesions by 96% in comparison to control groups. Furthermore, we observed a robust humoral and cellular immune response with production of high levels of protective lytic anti-α-Gal antibodies and induction of Th1 cytokines.

Conclusions/Significance

We propose that NGP5B is an attractive candidate for the study of potential synthetic α-Gal-neoglycoprotein-based vaccines against L. major infection.

Despite a worldwide prevalence, cutaneous leishmaniasis (CL) remains largely neglected, with no prophylactic or therapeutic vaccine available. In the Old World, CL is mainly caused by either Leishmania major or L. tropica parasites, which produce localized cutaneous ulcers, often leading to scarring and social stigma. Currently, the disease has reached hyperendemicity levels in the Middle East due to conflict and human displacement. Furthermore, the first choice of treatment in that region continues to be pentavalent antimonials, which are costly and highly toxic, and current vector control measures alone are not sufficient to stop disease transmission. Hence, a vaccine against CL would be very beneficial. Previous studies have demonstrated that sugars are promising vaccine candidates against leishmaniasis, since most parasite species have a cell surface coat composed of immunogenic sugars, including linear α-galactopyranosyl (α-Gal) epitopes, which are absent in humans. Here, we have developed an α-Gal-based vaccine candidate, named NGP5B. When tested in transgenic mice which like humans lack α-Gal epitopes in their cells, NGP5B was able to induce a significant partial protection against L. major infection, by significantly reducing mouse footpad lesions and parasite burden. Altogether, we propose NGP5B as a promising preventive vaccine for CL caused by L. major.

Comparison of the binding properties of the mushroom Marasmius oreades lectin and Griffonia simplicifolia I-B isolectin to alphagalactosyl carbohydrate antigens in the surface phase

The binding of two alpha-galactophilic lectins, Marasmius oreades agglutinin (MOA), and Griffonia simplicifolia I isolectin B(4) (GS I-B(4)) to neoglycoproteins and natural glycoproteins were compared in a surface phase assay. Neoglycoproteins carrying various alpha-galactosylated glycans and laminin from basement membrane of mouse sarcoma that contains the xenogenic Galalpha1-3Gal1-4GlcNAc epitope were immobilized in microtiter plate wells and lectin binding determined with an enzyme-linked assay. After 24 h of incubation, MOA had higher affinity for the xenogenic pentasaccharide (Galalpha1-3Gal1-4GlcNAcbeta1-3Galbeta1-4Glc) than for the Galalpha-monosaccharide. The binding properties of MOA and GS I-B(4) to the xenogenic disaccharide (Galalpha1-3Galbeta1) were comparable while the binding of MOA to the xenogenic pentasaccharide was much stronger than the binding of GS I-B(4) to the same epitope. Non-xenogenic disaccharide-coupled neoglycoproteins having galactose end groups linked alpha1-2 or alpha1-4 to Gal or linked alpha1-3 to GalNAc bound very weakly to MOA, whereas GS I-B(4) recognized all of these disaccharides with similarly high affinity. MOA also showed high affinity for laminin. The results indicate that the Marasmius oreades lectin has nearly the same affinities as does GS I-B(4) for the simple xenogenic carbohydrate antigens, but MOA has greater affinity for the pentasaccharide and is far more specific in its binding preferences than the Griffonia lectin.

Immunobiological features of the galactoside lectin L-Lc isolated from the Argentine mistletoe Ligaria cuneifolia

Ligaria cuneifolia has been used in Argentine folk medicine and is currently employed as substitute for the European mistletoe (Viscum album) as hypotensor agent. Extracts from V. album are widely used in cancer therapy and the antineoplasic effect is attributed to their cytostatic/cytotoxic and immunomodulatory actions. When studying immunomodulatory effects of L. cuneifolia extracts (Lc extracts), they inhibited proliferation of murine mitogen-activated lymphocytes, leukaemic lymphocytes (LB) and breast tumour cells (MMT). The aim of this work was to isolate and identify lectins from Lc extracts and investigate their immunobiological actions. A galactoside lectin (L-Lc) of 57 kDa was isolated. A polyclonal antiserum obtained against Lc extract recognised both L-Lc and MLI (V. album lectin), suggesting the possibility of shared epitopes. Treatment of LB tumour cells with L-Lc (0.01 and 0.1 microg/ml) produced up to 40.0+/-6.9% inhibition of cell growth, which seems partly mediated by apoptosis (apoptosis of L-Lc treated cells 58.4+/-10.3% versus non-treated cells 38.1+/-8.8%; P<0.05), analysed by acridine orange and ethidium bromide staining. Inhibitory effect on ConA stimulated splenocyte growth was non-significant, while a mitogenic effect was observed on normal murine splenocytes and MMT cells. L-Lc in non-cytotoxic concentrations (250 ng/ml) modified mRNA expression of IL-10 but neither that of TGF-beta nor of IL-2 produced by LB cells. In addition, 43.9+/-0.5% reduction in NO production by LPS-stimulated murine macrophages was found. Finally, survival rates of LB tumour-bearing mice treated or not with Lc extract or L-Lc failed to show significant differences.

Lectin interactions with alpha-galactosylated xenoantigens

alpha-Galactosylated xenoantigens (Galalpha1-3Galbeta1-4GlcNAcbeta1 and Galalpha1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc) are often detected with the alpha-Gal specific lectin Griffonia simplicifolia 1 isolectin B4 (GS1 B4). However, this lectin exhibits a broad and variable specificity for carbohydrates terminating in alpha-Gal. Thus, both false positive and false negative results may occur when GS1 B4 is used to determine natural antigens in xeno (pig-to-primate) transplantation research. To refine the tools for detecting alpha-galactosylated antigens we have studied the binding of various alpha-galactophilic lectins to alpha-galactosylated neoglycoproteins. The lectins were: Euonymus europaeus agglutinin (EEA), Griffonia simplicifolia 1 isolectin B4 (GS1 B4), Maclura pomifera agglutinin (MPA) and Pseudomonas aeruginosa agglutinin (PA-IL). Although both GS1 B4 and MPA strongly bound glycoconjugates terminating in Gal there seems to be some differentiation in their sugar binding preferences. MPA was the only lectin that showed high affinity for the pentasaccharide Galalpha1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc and for the Galalpha-glycans on non-primate thyroglobulin. The length of the xenoantigenic carbohydrate chain may influence the nature of the inhibition when a simple sugar is used to inhibit GS1 B4 binding to the xenoantigen. Inhibition studies of MPA GS1 B4 interaction further suggest that both lectins attach to the same site of the carbohydrate antigen and that GS1 B4 in addition binds to at least one other site that has no affinity for MPA. When lectins are used for recognition and investigation of natural Galalpha-antigens, we propose that GS1 B4 and MPA should accompany each other.

Probing the cons and pros of lectin-induced immunomodulation: case studies for the mistletoe lectin and galectin-1

When imagining to monitor animal cells through a microscope with resolution at the molecular level, a salient attribute of their surfaces will be the abundance of glycan chains. They present galactosides at their termini widely extending like tentacles into the extracellular space. Their spatial accessibility and their potential for structural variability endow especially these glycan parts with capacity to act as docking points for molecular sensors (sugar receptors such as lectins). Binding and ligand clustering account for transmission of post-binding signals into the cell interior. The range of triggered activities has turned plant lectins into popular tools in cell biology and immunology. Potential for clinical application has been investigated rigorously only in recent years. As documented in vitro and in vivo for the galactoside-specific mistletoe lectin, its apparent immunomodulatory capacity reflected in upregulation of production of proinflammatory cytokines will not necessarily be clinically favorable but a double-edged sword. In fact, lectin application has been shown to stimulate tumor growth in cell lines, histocultures of human tumors and in two animal models using chemical carcinogenesis or tumor transplantation. When testing immunological effects of the endogenous lectin galectin-1, protection against disorders mediated by activated T cells came up for consideration. Elimination of these cells via CD7-dependent induction of apoptosis, and a shift to the Th2 response by the galectin, are factors to ameliorate disease states. This result encourages further efforts with other galectins. Functional redundancy, synergism, diversity or antagonism among galectins are being explored to understand the actual role of this class of endogenous lectins in inflammation. Regardless of the results of further preclinical testing for galectin-1, these two case studies break new ground in our understanding how glycans as ligands for lectins convey reactivity to immune cells, with impact on the course of a tumor or autoimmune disease.

Isolation and characterization of major glycoproteins of pigeon egg white: ubiquitous presence of unique N-glycans containing Galalpha1-4Gal

Ovotransferrin (POT), two ovalbumins (POA(hi) and POA(lo)), and ovomucoid (POM) were isolated from pigeon egg white (PEW). Unlike their chicken egg white counterparts, PEW glycoproteins contain terminal Galalpha1-4Gal, as evidenced by GS-I lectin (specific for terminal alpha-Gal), anti-P(1) (Galalpha1-4Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glcbeta1-1Cer) monoclonal antibody, and P fimbriae on uropathogenic Escherichia coli (specific for Galalpha1-4Gal). Galalpha1-4Gal on PEW glycoproteins were found in N-glycans releasable by treatment with glycoamidase F. The respective contents of N-glycans in each glycoprotein were 3.5%, POT; 17%, POA(hi); and 31-37%, POM. POA(hi) has four N-glycosylation sites, in contrast to chicken ovalbumin, which has only one. High performance liquid chromatography analysis showed that N-glycans on POA(hi) were highly heterogeneous. Mass spectrometric analysis revealed that the major N-glycans were monosialylated tri-, tetra-, and penta-antennary oligosaccharides containing terminal Galalpha1-4Gal with or without bisecting N-acetylglucosamine. Oligosaccharide chains terminating in Galalpha1-4Gal are rare among N-glycans from the mammals and avians that have been studied, and our finding is the first predominant presence of (Galalpha1-4Gal)-terminated N-glycans.

Comparative study of theefficacy of removal of anti-ABO and anti-gal antibodies by double filtration plasmapheresis

Successful clinical ABO-incompatible renal transplantation has been achieved by the removal of anti-A or anti-B antibodies using double filtration plasmapheresis (DFPP). We have compared changes in the levels of anti-donor antibodies and the histopathology of the renal grafts following human ABO-incompatible allotransplantation and pig-to-baboon xenotransplantation using pretransplant DFPP. DFPP was performed on days 6, -4, -2 and -1 before the ABO-incompatible transplants (n=25) and on days -2 and 0 (immediately before reperfusion) in the xenotransplants (n=4). In two baboons (XenoTx Group I) the extent of antibody removal was comparable to that in the ABO-incompatible patients, and an even greater level of removal was achieved in another two baboons (XenoTx Group II). Anti-A and anti-B and anti-pig IgM and IgG antibodies were measured by flow cytometry. All clinical ABO-incompatible renal grafts are functioning, except two which were lost from recurrence of the original disease or from chronic rejection. Three other grafts underwent humoral rejection episodes, which were successfully treated. DFPP reduced the mean anti-A/B IgM and IgG antibody levels to 8% and 13% of pretreatment levels, respectively. After kidney transplantation, they were maintained at 37% and 46% of pre-DFPP level. No antibody binding to the transplanted kidney was detected at any time (1 h to 2 yr) after ABO-incompatible allotransplantation. In contrast, in XenoTx Group I, the same extent of antibody removal (90%) prevented hyperacute rejection, but the two grafts were rejected on days 6 and 7, respectively, from acute vascular rejection. In XenoTx Group II, the additional DFPP that was required to deplete the remaining 10% of anti-pig antibody was poorly tolerated and the two baboons died 4 h and 2 days, respectively, after renal transplantation. Although anti-pig IgM antibodies were reduced to 2% of pre-treatment level, IgM and C3 binding were detected in the graft as early as 1 h posttransplantation. These data suggest that the concentration of xeno-antigen epitopes expressed on pig organs may need to be reduced by genetic engineering to the much lower level of blood group A/B antigens on human kidneys if discordant xenotransplantation is to be successful.

Human and non-human primate anti-galactosyl response after injection of rat monoclonal antibody bearing galactosyl epitopes

In the case of clinical use of pig-to-human xenografting, any exogenous source of to-galactosyl epitopes will elicit an anti-galactosyl immune response, which could be deleterious for the xenograft. The presence of Galalpha(1-3)Gal residues was thus examined by western blotting on various rat monoclonal antibodies (mAb), which are used in clinical trials. In parallel, the anti-galactosyl humoral response was assessed in the serum of kidney allograft recipients and experimental baboons, which received these mAbs. Galactosyl residues were evidenced on all rat monoclonal antibody tested. The anti-galactosyl response was weak in kidney allograft recipients receiving a basic immunosuppression (Cyclosporine, Azathioprine, Prednisolone) and iterative injections of rat mAbs. In contrast, untreated or immunosuppressed baboons that received rat mAbs developed a major anti-galactosyl humoral response. These results suggest that anti-galactosyl sensitization produced by therapeutic agents will have to be considered in the case of clinical xenotransplantation.

Association of concentration of asbestos and asbestos-like fibers with the patient's survival and the binding capacity of lung parenchyma to galectin-1 and natural alpha-galactoside- and alpha-mannoside-binding immunoglobulin G subfractions from human serum

Our aim in this study was to search for lung parenchyma alterations associated with asbestos and/or asbestos-like fiber concentration. This was done by means of immuno- or glycohistochemistry. The hot-ashing technique determined the asbestos and asbestos-like fiber concentrations in the lung tissues of 100 patients of whom 52 were treated for primary lung and 25 for secondary lung tumors; fiber concentration was also measured for 23 patients whose disease was benign. The results were correlated to smoking habits, survival of the patients, and expression of binding capacities for endogenous lectins, natural carbohydrate-binding and lectin-specific antibodies. The cohort with proven asbestos exposure revealed a mean fiber concentration 114 f/g compared to 95 f/g in the non-exposed group. An increased asbestos fiber concentration was correlated to galectin-1-binding and the presence of epitopes for natural immunoglobulin G subfractions with selectivity to alpha-galactosides and alpha-mannosides. The survival of patients with primary and secondary lung tumors was negatively associated with the fiber concentration. The data indicate that increased presence of asbestos is correlated with an alteration of defined glycohistochemical features of alveolar lining cells.

Immunohistologic evaluation of mechanisms mediating hyperacute lung rejection, and the effect of treatment with K76-COOH, FUT-175, and anti-Gal column immunoadsorption

Although most investigators agree that lung dysfunction occurs rapidly in various pig-to-primate hyperacute lung rejection (HALR) models, the basic mechanisms mediating this phenomenon remain in question. Here we describe an immunohistochemical method for assessment of mechanisms driving HALR. Using an established model wherein piglet lungs are perfused ex vivo with human blood, six experimental groups (K76 COOH; FUT-175; K76 with FUT; anti-alpha-Gal column adsorption; column with FUT; and column with K76) and two control groups (unmodified human blood; autologous pig blood) were studied. Each lung was biopsied serially during perfusion, and assessed using an immunohistochemical technique, with vWF staining as an internal control to quantitate binding of human IgM, IgG, C3, C5b-9, properdin, and C1q. The effect of each treatment and subsequent lung perfusion on IgG and IgM anti-alpha-Gal titers(by ELISA) and on pig endothelial cell cytotoxicity were correlated with histologic findings. We found that [1] the classical complement activation pathway was activated, as has been shown for other pig organs in primate or human blood environments [2]; alternative complement pathway activation is also seen, which has not been described for other organs in pig-to-primate models, but only in the context of classical pathway activation; and [3] anti-Gal column absorption, pharmacologic inhibition of complement, or combination therapy each was associated with histologic evidence of partial protection, consistent with what would be predicted for each intervention. Further, immunohistologic differences correlated with physiologic outcomes [8] and with antibody assay results, and revealed that treatments used were incompletely effective. Our data suggest that more complete inhibition of antibody- and complement-driven pathways than was achieved in these experiments will be necessary to prevent the antibody and complement-mediated facets of hyperacute lung rejection. This immunohistologic technique may also help us identify additional pathogenic mechanisms important to eventual clinical application of pig-to-human lung xenografts.

Naturally occurring anti-alpha-galactosyl antibodies: relationship to xenoreactive anti-alpha-galactosyl antibodies

Antibodies produced by an individual without a known history of sensitization to the relevant antigen are called "natural" antibodies. Some natural antibodies, called xenoreactive antibodies, react with the cells of foreign species. Most xenoreactive antibodies in humans and higher primates bind to a nonreducing terminal galactose expressed by pigs and other lower mammals. Although human natural antibodies which bind to one or more of a variety of terminal alpha-galactosyl structures have been identified previously, the antigen recognized by anti-alpha-galactosyl antibodies on the cells of foreign species is thought to be exclusively Galalpha1-3Gal. Thus, anti-alpha-galactosyl antibodies which do not react with Galalpha1-3Gal are thought to be nonxenoreactive. Here, we identify natural antibodies in human serum which bind to Galalpha1-6Hexosepyrranosides but not Galalpha1-3Gal, indicating that these antibodies are not xenoreactive. Various lower mammals were found to have natural anti-Galalpha1-2Gal antibodies in their sera, suggesting that at least some anti-Galalpha1-2Gal antibodies might not be xenoreactive and indicating, surprisingly, that anti-alpha-galactosyl antibodies are much more phylogenetically disperse than previously known. Also surprising was the finding that some natural antibodies which bind to Galalpha1-3Gal in vitro do not bind to porcine xenografts. These studies show that naturally occurring anti-alpha-galactosyl antibodies in mammalian serum include antibodies with a greater variety of reactivities than previously thought, only some of which would bind to a porcine xenograft. Further, these studies show that the methods used to detect anti-alpha-galactosyl antibodies of relevance in xenotransplantation must be carefully evaluated to avoid detection of anti-alpha-galactosyl antibodies which would not bind to a porcine organ and which therefore are not involved in xenograft rejection.

Pharmacologic immunosuppressive therapy and extracorporeal immunoadsorption in the suppression of anti-alphaGal antibody in the baboon

The aim of this study was to deplete baboons of anti-(alpha)galactosyl (alphaGal] antibody and attempt to maintain depletion by pharmacologic immunosuppressive therapy (PI). In 12 experiments, involving nine baboons, repeated extracorporeal immunoadsorption (EIA) was carried out by plasma perfusion through immunoaffinity columns of synthetic alphaGal trisaccharide type 6. Five of the baboons were immunologically naive and four had undergone various procedures at least 6 months previously. All, however, had recovered lymphohematopoietic function and (with one exception) had levels of anti-alphaGal antibody within the normal range. Eleven protocols included continuous i.v. cyclosporine (to maintain whole blood levels of approximately 1,600 ng/ml). In addition, in ten protocols, the baboon received one or more of the following drugs: cyclophosphamide (1-20 mg/kg/day), mycophenolate mofetil (70-700 mg/ kg/day), brequinar sodium (1-12 mg/kg/day), prednisolone (1 mg/kg/day), melphalan (0.15-0.6 mg/kg/day), methylprednisolone (125 mg/day x3), and antilymphocyte globulin (ATG) (50 mg/kg/day x3). EIA was carried out on 1-9 occasions in each study and was temporarily successful in removing all antibody. When no PI was administered, antibody returned close to pre-EIA levels within 48 hr. Cyclosporine alone delayed the rate of antibody return only slightly. While EIA was continuing on a daily or alternate day schedule, antibody levels (both IgM and IgG) were maintained at 20-45% of pre-EIA levels. Once EIA was discontinued but PI maintained, IgM rose to 40-90% and IgG to 30-60% of pre-EIA levels. In vitro testing demonstrated significant cytotoxicity to pig cells at these antibody levels. We conclude that i) EIA utilizing columns of alphaGal trisaccharide is successful in temporarily depleting baboons of anti-alphaGal antibody, but ii) none of the PI regimens tested suppressed antibody production to levels which would be expected to prevent antibody-mediated rejection of pig xenografts. Additional strategies will therefore be required if xenotransplantation is to become a clinical reality.

Fusion of macrophages on an implant surface is associated with down-regulated expression of ligands for galectin-1 and -3 in the rat

Galectins have a wide range of biological activities which are elicited by binding to appropriate glycoligands. Besides regulation of the expression of the galectins the extent of the presence of suitable binding sites will be relevant to infer the cellular responsiveness to this class of sugar receptors. Thus ligand presentation requires monitoring by the tissue lectin. We demonstrate the expression of galectin-3 by macrophages and foreign-body giant multinucleate cells colonizing a cellophane implant in the rat by the A1D6 monoclonal antibody. The extents of ligand presence are visualized in the same cells by biotinylated galectin-3 and also by galectin-1 which is produced by diverse mammalian cell types and widely distributed. Labeled mistletoe (VAA) and tomato (LEA) lectins are used as tools to assess the degree of similarity of the binding profile between endogenous and exogenous proteins. The presentation of alpha-galactosides is monitored with a natural immunoglobulin G subfraction obtained by two consecutive affinity chromatography steps. The binding of labeled galectins and plant lectins was significantly lower to foreign-body giant multinucleate cells than to mononuclear macrophages. The application of the alpha-galactoside-specific probe yielded no significant staining. The potential problem of epitope accessibility could be excluded by the concomitant positivity obtained with an IgG subfraction with selectivity to beta-galactosides also obtained by affinity chromatography. These results provide no evidence for a role of alpha-galactosides for the binding of galectins in the rat macrophages colonizing the implant. The reduced level of expression of glycoligands for galectin-1 and -3 in foreign-body giant multinucleate cells in contrast with the mononuclear macrophages suggests an inhibitory influence of macrophage fusion on the expression of galectin-reactive molecules.

Reduction of the major swine xenoantigen, the alpha-galactosyl epitope by transfection of the alpha2,3-sialyltransferase gene

alpha2,3-Sialyltransferase represents a putative enzyme that reduces the Galalpha1-3Gal beta1-4GlcNAc-R (the alpha-galactosyl epitope) by intracellular competition with alpha1,3-galactosyltransferase for a common acceptor substrate. This study demonstrates that the overexpression of the alpha2,3-sialyltransferase gene suppresses the antigenicity of swine endothelial cells to human natural antibodies by 77% relative to control cells and by 30% relative to cells transfected with alpha1,2-fucosyltransferase, and in addition, it reduces the complement-mediated cell lysis by 75% compared with control cells and by 22% compared with cells transfected with alpha1, 2-fucosyltransferase. The mechanism by which the alpha-galactosyl epitope was reduced was also studied. Suppression of alpha1, 3-galactosyltransferase activity by 30-63% was observed in the transfectants with alpha2,3-sialyltransferase, and mRNA expression of the alpha1,3-galactosyltransferase gene was reduced as well. The data suggest that the alpha2,3-sialyltransferase effectively reduced the alpha-galactosyl epitope as well as or better than the alpha1, 2-fucosyltransferase did and that the reduction of the alpha-galactosyl epitope is due not only to substrate competition but also to an overall reduction of endogenous alpha1, 3-galactosyltransferase enzyme activity.

Characterization of a polyclonal anti-Galalpha1-3Gal antibody from chicken

A polyclonal antibody was raised against the Galalpha1-3Gal carbohydrate epitope, which is expressed by all mammals (except man and the closest primate species) by immunizing hens with rabbit erythrocyte membranes. IgY was isolated from egg yolks, and affinity-purified on a Galalpha1-3Gal-Synsorb column. Two percent of the initial IgY fraction was recovered. The specificity of the affinity-purified antibody was characterized by: absorption with human, rabbit and pig erythrocytes; by using Synsorb columns; by inhibition with different saccharides; and by immunostaining of glycolipids separated on thin layer chromatograms. A weak reactivity was found toward blood group B or blood group Pk determinant, depending on the assay system used. Such reactivities were abolished after absorption by the appropriate sorbents, yielding a polyclonal anti-Galalpha1-3Gal antibody with narrow specificity.

Expression of alpha-1,3-galactose and other type 2 oligosaccharide structures in a porcine endothelial cell line transfected with human alpha-1,2-fucosyltransferase cDNA

The binding of xenoreactive natural antibodies to the Galalpha1-3Galbeta1-4GlcNAc (alpha-galactose) oligosaccharide epitope on pig cells activates the recipient's complement system in pig to primate xenotransplantation. Expression of human alpha-1, 2-fucosyltransferase in pigs has been proposed as a strategy for reducing the expression level of the alpha-galactose epitope, thereby rendering the pig organs more suitable for transplantation into humans. The aim of this study was to examine how the cell surface expression of alpha-galactose, H, and related fucosylated and sialylated structures on a pig liver endothelial cell line is affected by transfection of human alpha-1,2-fucosyltransferase cDNA. Nontransfected and mock-transfected cells expressed alpha-galactose, alpha-2,3-sialylated, and alpha-2,6-sialylated epitopes strongly, with low level expression of type 2 H and LewisX. By contrast, expression of the H epitope was increased 5-8-fold in transfected cells with a 40% reduction in the expression of alpha-galactose epitope and a 50% decrease in sialylation, as measured by binding of Maackia amurensis and Sambuccus nigra agglutinins. LewisX expression was reduced to background levels, while the LewisY neoepitope was induced in human alpha-1,2-fucosyltransferase-expressing pig cells. The activities of endogenous alpha-1,3-galactosyltransferase, alpha-1,3-fucosyltransferases, and alpha-2,3- and alpha-2, 6-sialyltransferases acting on lactosamine were unaffected. Our results show that a reduction in alpha-galactose epitope expression in porcine endothelial cells transfected with human alpha-1, 2-fucosyltransferase cDNA may be achieved but at the expense of considerable distortion of the overall cell surface glycosylation profile, including the appearance of carbohydrate epitopes that are absent from the parent cells.

Anti-galectin-1 autoantibodies in serum of patients with neurological diseases

The presence of autoantibodies to human brain galectin-1 was investigated in serum from patients with multiple sclerosis, patients with or without evidence of other neurological disorders, and healthy controls, using an ELISA on purified brain galectin-1. Levels of autoantibodies to galectin-1 were significantly higher in patients than in healthy controls. Comparison of levels of anti-galectin-1 and anti-idiotypic antibodies mimicking human brain galectin-1 (L-IgG) showed that the highest levels of autoantibodies were present in patients with low levels of L-IgG. This finding can be explained by hypothesizing that the concentration of autoantibodies to galectin-1 is possibly associated with impairment of the regulation of the immune system.

Anti-GaL IgG antibodies in sera of newborn humans and baboons and its significance in pig xenotransplantation

We have previously demonstrated that hyperacute rejection does not occur in a pig-to-newborn baboon heart transplant model, presumably because of low levels of cytotoxic antipig antibodies present in the serum of newborn baboons. Cytotoxic antipig antibodies are primarily directed to alpha-1,3-galactosyl (alpha Gal) residues on endothelial cell surface structures Twenty-one full-term humans and 5 full-term baboons were tested for complement mediated lysis (CML) of pig kidney (PK-15) cells and anti-alpha Gal activity with an ELISA using BSA-conjugated alpha Gal residues as target. To evaluate the significance of the anti-alpha Gal titers in vivo 5 newborn baboons underwent heterotopic pig cardiac xenotransplantation. Six of 21 human samples and 1 of 5 baboon samples demonstrated significant cytotoxicity to PK-15 cells. Twelve of 21 newborn humans had anti-alpha Gal IgG antibodies at titers of 1:80 or greater. None of the samples had anti-alpha Gal IgM. In newborn baboons, 1 of 5 sera had anti-alpha Gal IgG antibodies at titers greater than 1:80 and none of these samples had anti-alpha Gal IgM. Xenografts survived for an average of 3.6 days, even in the baboon with high anti-alpha Gal IgG titers. Analysis of the explanted grafts showed minimal evidence of complement-mediated hyperacute rejection (HAR), but prominent mononuclear cell infiltrates. In serum tested posttransplant there was an induced anti-alpha Gal response with cytotoxicity against PK-15 cells. These results show that anti-alpha Gal IgM is absent in newborn human and baboon sera, allowing pig grafts to avoid HAR. However, the presence of anti-alpha Gal IgG may be associated with mononuclear cell infiltration of the xenograft and its subsequent rejection.

Removal of terminal alpha-galactosyl residues from xenogeneic porcine endothelial cells. Decrease in complement-mediated cytotoxicity but persistence of IgG1-mediated antibody-dependent cell-mediated cytotoxicity

To determine the role of the terminal alpha-galactosyl residue in the endothelial damage mediated by human xenoreactive natural antibodies (IgM and IgG), we treated porcine endothelial cells in culture with green coffee bean alpha-galactosidase. A practically complete removal of terminal alpha-Gal residues (as evaluated by flow cytometry with Bandeiraea simplicifolia isolectin B4) and concomitant exposure of N-acetyllactosamine were obtained without altering cell viability. A dramatic decrease in IgM and IgG binding (from a pool of human sera) was observed, confirming the key role of the alpha-galactosyl residues. The enzyme treatment did not induce any nonspecific immunoglobulin binding sites, but led to the exposure of new epitopes for a minor fraction of IgM. The main residual IgM and IgG binding could be due to xenoantigens other than the alpha-galactosyl residues. When alpha-galactosidase-treated endothelial cells were used as targets in cytotoxicity experiments, they were less susceptible than untreated cells to complement-mediated cytotoxicity induced by fresh human serum. In contrast, they did not acquire resistance to human IgG-dependent cellular cytotoxicity, despite the decrease in IgG binding. Because it is known that antibody-dependent cytotoxicity mediated by CD16+ NK cells is dependent on IgG1 and IgG3, and not on IgG2 or IgG4, which was confirmed by blocking experiments, we studied the binding of all four subclasses to intact and alpha-galactosidase-treated endothelial cells. Two major subclasses, IgG1 and IgG2, bound to untreated endothelial cells, whereas IgG3 binding was low and IgG4 binding was negligible. A decrease in IgG1, IgG2, and IgG3 binding was observed upon alpha-galactosidase treatment, indicating that antibodies belonging to these three subclasses recognize alpha-galactosyl residues. The decrease in IgG2 binding was more pronounced than the decrease in IgG1 binding. Collectively, these data indicate that IgG1 xenoreactive natural antibodies, including those which are not directed at the alpha-galactosyl residues, could play a major role in the early delayed vascular rejection of pig xenografts.

Synthesis of alpha-galactosyl epitopes by recombinant alpha1,3galactosyl transferase for opsonization of human tumor cell vaccines by anti-galactose

The immunogenicity of tumor-associated antigens in autologous tumor vaccines is limited because of insufficient uptake by antigen-presenting cells (APC). Anti-Galactose (Gal) IgG, abundantly produced in humans, can serve as a natural adjuvant increasing the uptake of vaccinating autologous tumor cell membranes by APC. Anti-Gal interacts with the alpha-galactosyl epitope (Ga1alpha1-3Galbeta1-4GlcNAc-R), which is normally absent in humans. This epitope is produced in large amounts in nonprimate mammals and New World monkeys due to the intracellular activity of the glycosylation enzyme alphal,3galactosyltransferase. alpha-Galactosyl epitopes were synthesized in vitro on human tumor cells by soluble recombinant alphal,3galactosyltransferase. Anti-Gal binding to these epitopes induces the effective uptake of the tumor cells by APC with Fc receptors that interact with the Fc portion of this natural antibody. It is suggested that synthesis of alpha-galactosyl epitopes on freshly isolated human tumor cell membranes, followed by their administration back to the patient, will result in the in situ opsonization of the membranes by anti-Gal, thereby improving the uptake, processing, and presentation of autologous tumor-associated antigens by APC with Fc receptors.

Specificity of xenoreactive anti-Gal alpha 1-3Gal IgM for alpha-galactosyl ligands

The transplantation of organs from lower animals such as pigs into humans is prevented by a severe rejection reaction initiated by complement fixing xenoreactive natural antibodies. Most anti-pig xenoreactive natural antibodies in humans are thought to recognize Gal alpha 1-3Gal beta 1-4GlcNAc and are also thought to recognize, albeit less avidly, Gal alpha 1-6Glc. Gal alpha 1-6Glc has been used as a ligand for purification of 'anti-Gal alpha 1-3Gal antibodies' and as a therapeutic or reagent to prevent the binding of these antibodies to porcine organs or cells. We tested the specificity of anti-Gal alpha 1-3Gal IgM for Gal alpha 1-6Glc and related saccharides. Based on inhibition of binding of xenoreactive anti-Gal alpha 1-3Gal IgM to porcine cells by soluble saccharides, anti-Gal alpha 1-3Gal IgM in a human serum was found to consist of a mixture of antibodies which have a similar affinity for Gal alpha 1-3Gal but varying affinities for Gal alpha 1-6Glc and other structures. Twenty to 40% of the anti-Gal alpha 1-3Gal IgM from the population tested did not recognize Gal alpha 1-6Glc. The binding of anti-Gal alpha 1-3Gal IgM to Gal alpha 1-6Glc varied widely from individual to individual, some samples lacking almost entirely anti-Gal alpha 1-3Gal IgM which bound to Gal alpha 1-6Glc.

Enhancement of antigen presentation of influenza virus hemagglutinin by the natural human anti-Gal antibody

Immunogenicity of inactivated virus or subviral vaccines may be enhanced by complexing with an IgG antibody. Such antibody would increase the uptake, processing and presentation of the vaccine's antigens by antigen presenting cells (APC), via the adhesion of the antibody-vaccine complex to Fc-receptors on macrophages and other APC. A natural antibody in humans, which may be generally exploited for this purpose, is the natural anti-Gal antibody. This antibody is ubiquitously produced as 1% of circulating IgG in humans and Old World primates, and it interacts specifically with the carbohydrate epitope Gal alpha 1-3 Gal beta 1-4 GlcNAc-R (termed the alpha-galactosyl epitope). This epitope is synthesized in large amounts in cells of nonprimate mammals and New World monkeys by the glycosylation enzyme alpha 1,3 galactosyltransferase. Here we describe in vitro studies on the ability of anti-Gal to bind to alpha-galactosyl epitopes on influenza virus propagated in mammalian cells, and to enhance presentation by APC of viral hemagglutinin antigenic determinants to specific helper T cell clones. The various approaches for achieving alpha-galactosyl epitope expression on virion and subviral vaccines are discussed.

Changes in isotype composition and antigen recognition of anti-Trypanosoma cruzi antibodies from acute to chronic Chagas disease

This report describes differences in humoral immune response of acute and chronic phases of human Chagas disease. The reactivities of IgG, IgM, and IgA anti-Trypanosoma cruzi antibodies in serum samples from both groups of patients were compared by enzyme-linked immunosorbent assay (ELISA) employing either one of four antigenic fractions: mouse laminin (LAM), which reacts through Gal alpha 1-3Gal epitopes expressed on trypomastigote surface: whole intact trypomastigotes (TCT); trypomastigotes excreted/secreted antigens (TESA); and epimastigote alkaline extract (EAE). The selection of T. cruzi antigen preparations was based on their relative content of surface and internal antigens found in trypomastigote forms. The proportion of IgG reactive to carbohydrate epitopes was assessed through the decay of IgG reactivity from acute and chronic sera after m-periodate oxidation of solid-phase bound antigens. Trypomastigote and TESA antigens recognized by IgG from acute and chronic sera were also compared by immunoblotting. ELISA and immunoblotting data showed that: (1) the proportion of IgG directed to trypomastigote surface antigens was higher in acute than in chronic sera, whereas the opposite was found for internal antigens, (2) acute sera contained a higher percentage of IgG reactive to trypomastigote carbohydrate epitopes than chronic sera, and (3) anti-T. cruzi IgA was found exclusively in acute sera and led to 100% positivity when LAM, TCT, and TESA were employed as antigens. IgA ELISA with these antigens and IgG immunoblotting pattern with TESA could be useful as serological markers for the acute phase of human Chagas disease.

Characterization of human IgG-binding xenoantigens expressed by porcine aortic endothelial cells

Xenoreactive antibodies (XAb) play a major role in the rejection of xenografts. In this study, human IgG XAb that bind to xenoantigens expressed by porcine aortic endothelial cells (PAEC) were characterized, together with their corresponding xenoantigens. Using an ELISA with both fixed and unfixed confluent monolayers of PAEC, XAb of both IgG and IgM classes in pooled and individual normal human serum were identified. The binding of these IgG XAb to the endothelium is mediated by F(ab')2 and the only detectable subclasses that bind to the endothelium are IgG1 and IgG2. On the basis of direct binding experiments, inhibition and antibody adsorption studies, and enzymatic digestions, it is shown that only a minor component of the XAb binding is directed against galactose in an alpha 1,3 linkage with galactose on PAEC surfaces. There is some cross-reactivity with antigens expressed on porcine lymphocytes, but not porcine red blood cells. Histological examination of sections of porcine aortae, snap-frozen and stained using immunoperoxidase techniques, confirmed interaction with the vascular endothelium. Labeling of the PAEC with 125I, followed by cell lysis and immunoprecipitation under reducing conditions, showed binding of IgG XAb to several components on the endothelial cell surface, the most prominent of which have apparent molecular masses of 75 kDa, 110 kDa, 180 kDa, and 210 kDa. The 110-kDa component and the 180-kDa component were sensitive to digestion with endoglycosidase F, which suggests the participation of N-linked carbohydrate structures. These studies demonstrate that human IgG XAb recognize multiple determinants expressed by PAEC, a minor population of which contain alpha 1,3-linked galactose residues. Cross-reactive determinants are expressed on porcine lymphocytes but not porcine red blood cells.

Carbohydrate-binding proteins (plant/human lectins and autoantibodies from human serum) as mediators of release of lysozyme, elastase, and myeloperoxidase from human neutrophils

Analysis of cell surface glycosylation not only provides information about cell properties such as their state of differentiation or histogenetic lineage. The carbohydrate chains also provide potentially functional binding sites to endogenous carbohydrate-binding proteins. This interaction can elicit consequent signalling processes. Because of the importance of neutrophils in the host defence system, we monitored the effect of the binding of such sugar receptors to their cell surface on the release of the enzymatic activities of lysozyme, elastase, and myeloperoxidase. Besides the mannose-binding lectin concanavalin A and the immunomodulatory alpha/beta-galactoside-binding lectin from Viscum album L., three preparations of human sugar receptors - beta-galactoside-binding lectin (M(r) 14 kDa) and two affinity-purified polyclonal IgG fractions from serum with the capacity to recognize alpha- or beta-galactosides, respectively - were used. Two animal lectins from chicken liver and intestine that bind beta-galactosides, as well as the lectin-like human serum amyloid P component, were included in order to assess the importance of slight differences in ligand recognition. Cytochalasin B-enhanced enzyme release was invariably seen with the two plant lectins and the chicken liver beta-galactoside-binding lectin, but the related intestinal lectin did not increase enzyme release. The mammalian homologue of these avian lectins triggered lysozyme secretion, and the lactoside-binding IgG fraction enhanced the amount of extracellular elastase activity slightly but significantly. Thus, the actual lectin, not the nominal specificity of sugar receptors, is crucial for elucidation of responses. Due to the highly stimulatory activity of the two plant lectins, neutrophils from patients with non-cancerous diseases and from patients with lung cancer were monitored for the extent of lectin-mediated enzyme release. Only the concanavalin A-mediated reactivity of the neutrophils was associated with the type of disease.

Differential binding of two chicken beta-galactoside-specific lectins to homologous lymphocyte subpopulations and evidence for inhibitor activity of the dimeric lectin on stimulated T cells

Plant lectins can be potent modulators of vertebrate immune functions. Biochemical characterization of lectins from animal tissues enables the determination of whether these endogenous activities display a comparable immunological potency. Focusing on chicken beta-galactoside-binding lectins, the monomeric intestinal (CL-14) and the dimeric liver lectin (CL-16) were purified and the lack of cross-contamination was ascertained. In very close agreement with the molecular masses of 14,974 and 14,976 calculated on the basis of the available sequence data (Y. Sakakura et al., J. Biol. Chem. 265, 21573-21579, 1990), electrospray mass spectrometric analysis yielded values of 14,969 (CL-14) and 14,972 (CL-16), the reasons for the deviation in gel electrophoretic behavior being unclear. Solid-phase assays with immobilized lactosylated poly-L-lysine demonstrated a comparatively lower affinity and higher extent of binding at saturation for the monomeric lectin than for the dimeric protein, whose properties were similar to those of an immunomodulatory plant lectin. Flow cytometry revealed homogeneous and strong binding of the dimeric lectin within the chicken peripheral blood lymphocyte population, whereas the monomeric lectin stained two subpopulations at different intensities. Two-color flow cytometry disclosed preferential binding of this lectin to B cells. When a B cell line was employed for determination of affinity constants and extents of binding at saturation, qualitatively comparable parameters to those for the solid-phase assays were obtained. The similar profile of lectin-binding glycoproteins in blots of cellular extracts underscored that accessibility to ligands, not qualitatively different ligand display, may explain the differences for the cell line. At up to a concentration of 10 micrograms/ml of the lectins no stimulation of [3H]thymidine incorporation was seen for blood and spleen cell populations. However, the dimeric lectin reduced stimulation of cells that were responsive to an anti-TcR2 antibody. Thus, this lectin can apparently exhibit inhibitory activity to this kind of T cell activation in vitro.

Respiratory burst of human polymorphonuclear leukocytes in response to the galactoside-specific mistletoe lectin

The phagocytic activity of human polymorphonuclear leukocytes (PMNLs) towards Staphylococcus aureus Cowan 1 was evaluated in chemiluminescence assays. As to check its activating ability, galactoside-specific mistletoe lectin (ML-1) was coincubated with PMNLs which were then challenged with S. aureus. Statistically significant (p < 0.001) chemiluminescent response (correlating with phagocytic activity) could be demonstrated at optimal experimental condition, viz: 1 x 10(6) PMNLs incubated with 0.005 ng ML-1 for 30 and 60 minutes before S. aureus challenge. Other experimental schedules (different timing and PMNL/ML-1 concentrations) did not present with statistically relevant changes in chemiluminescent response. These studies suggest that optimal ML-1 concentrations enhance the phagocytic activity of PMNLs which might be of benefit in thus treated patients as to prevent (or lower the rate of) infections under antineoplastic therapy.

Essential residues in V(D)J recombination signals

Recombination signal sequences for V(D)J joining consist of a conserved heptamer (CACAGTG) and a nonamer (ACAAAAACC) separated by a spacer of a constant length (12 bp or 23 bp). In the present study, we have analyzed various recombination signal mutations for their effects in V(D)J joining. Using a retroviral vector, we introduced mutant substrates stably into pre-B cells, and assayed recombination using the lacZ gene as a reporter. This method allowed us to study recombination in a single copy within the context of the host cell chromosome. Because this assay did not show any detectable background, it was quite useful in the analysis of low level recombinations. In the heptamer, mutations in the first three residues severely dropped the joining rates. Among them, the first residue adjacent to the recombination site was found to be most essential. Although mutations in the heptamer reduced the joining rate to various extents, they did not lower the site-specificity of recombination. With regard to the nonamer, the presence of three consecutive A residues was necessary for efficient recombination. Furthermore, the nucleotides flanking the A-rich core needed to be other than A residues, probably marking the border of the A-stretch. This may be important when the recombinase measures the distance between the heptamer and the nonamer to satisfy the 12/23-bp spacer rule.

Characterization and affinity isolation of xenoreactive human natural antibodies

Natural Abs, which are thought to provide an initial defense against invasive microorganisms, include isohemagglutinins, anti-phosphatidylcholine Abs, and anti-alpha-galactose Abs. We have evaluated the physiologic properties of the fraction of human natural Abs that bind to porcine endothelial cells and that would, as a result, initiate the rejection of a porcine organ transplanted into a human. The concentration of xenoreactive IgM in the serum varied widely in the population (5 to 105 micrograms/ml), but was highly dependent on the concentration of IgM in the serum (r = 0.85). Despite this variation and the potential diversity of epitopes recognized, human xenoreactive natural Abs exhibited surprisingly homogeneous binding characteristics, both in one individual and in the population. The apparent avidity determined by using a direct ELISA yielded a functional dissociation constant of 10(-8) M to 10(-10) M, depending on the temperature used. This high functional Kd apparently results from polyvalent interactions between the IgM and the porcine cell surface. Although the xenoreactive IgMs were absorbed by structurally diverse molecules such as ssDNA and thyroglobulin, about 80% of the xenoreactive Abs were specific for the terminal alpha-galactose determinant. A method was developed for affinity isolation of xenoreactive natural Abs by using a thermal extraction procedure. The method quantitatively accounts for all xenoreactive IgM, yielding functional IgM as evidenced by Ag binding and complement activation. Given the overlapping specificity of xenoreactive Abs in the population and the homogeneity of the functional Kd, the natural humoral immunologic barrier to xenotransplantation may be far less formidable than previously thought.

Specific stimulation of Graves' disease thyrocytes by the natural anti-Gal antibody from normal and autologous serum

Anti-Gal is a natural Ab abundantly produced in humans. It interacts specifically with the carbohydrate epitope Gal alpha 1-3Gal beta 1-4GlcNAc-R (termed the alpha-galactosyl epitope). This epitope is expressed in large amounts on thyrocytes of nonprimate mammals, but not of humans. We have previously found that binding of anti-Gal to alpha-galactosyl epitopes on porcine thyrocytes results in stimulatory effects similar to those exerted by thyroid-stimulating hormone (thyrotropin). In the present study, we tested the hypothesis that anti-Gal may contribute to Graves' disease (GD) pathogenesis by stimulation of the thyrocytes of patients with this autoimmune disorder. Anti-Gal binding and stimulatory effects were assessed in primary thyrocyte cultures. Anti-Gal specifically bound to GD thyrocytes and induced an increase in cAMP synthesis, 125I uptake, and DNA synthesis in these cells. Furthermore, the stimulatory effects of autologous sera on GD thyrocytes were greatly reduced after specific depletion of anti-Gal from these sera. No binding and no stimulatory effects of anti-Gal were observed, however, with normal human thyrocytes and with thyrocytes from thyrotoxic patients who lack thyroid-stimulating Igs or thyrotropin binding inhibiting Igs. These in vitro stimulatory effects of anti-Gal on GD thyrocytes suggest that this natural Ab may contribute to the in vivo continuous stimulation of thyrocytes in GD patients. The possibility that anti-Gal may stimulate GD thyrocytes via interaction with aberrantly expressed alpha-galactosyl epitopes on the thyroid-stimulating hormone receptor is discussed.

Differential host-dependent expression of alpha-galactosyl epitopes on viral glycoproteins: a study of eastern equine encephalitis virus as a model

The carbohydrate epitope Gal alpha 1-3Gal beta 1-4GlcNAc-R (alpha-galactosyl) is abundantly expressed on cells of non-primate mammals, prosimians and New World monkeys, where it is synthesized by the enzyme alpha 1,3-galactosyltransferase (alpha 1,3GT). Old World monkeys, apes and humans lack alpha 1,3GT and hence do not synthesize alpha-galactosyl epitopes. Instead, these species produce a natural antibody, anti-Gal, which interacts specifically with alpha-galactosyl epitopes and which constitutes up to 1% of circulating immunoglobulins in humans. We have used eastern equine encephalitis (EEE) virus as a model to examine the differential expression of alpha-galactosyl epitopes on the glycoproteins of virus propagated in cells that either produce or lack alpha 1,3GT. As predicted, virus propagated in Vero cells (derived from the African green monkey, an Old World monkey) did not express alpha-galactosyl epitopes. In contrast, virus propagated in mouse 3T3 cells (EEE3T3) expressed approximately 80 alpha-galactosyl epitopes per virion on both the E1 and the E2 envelope glycoproteins. Thus, expression of the alpha-galactosyl epitope on virions paralleled that on host cells. The binding of anti-Gal antibody to these epitopes on EEE3T3 virions partially neutralized virus infectivity, raising the possibility that anti-Gal production in hosts may influence the initial infectious stage of viruses expressing alpha-galactosyl epitopes.

Anti-pig IgM antibodies in human serum react predominantly with Gal(alpha 1-3)Gal epitopes

A major problem with pig-to-human-tissue xenograft studies is that humans have natural antibodies to pig cells; these antibodies would cause hyperacute rejection if pig tissues were xenografted to humans. Here we show that most of human IgM antibodies present in the serum of healthy donors and reactive with pig cells react with galactose in an (alpha 1-3) linkage with galactose--i.e., Gal(alpha 1-3)Gal. Absorption studies demonstrated that the antibodies detected the same or similar epitopes on the surface of pig erythrocytes, blood and splenic lymphocytes, and aortic endothelial cells (EC). The antibodies were sensitive to 2-mercaptoethanol (2ME) treatment, did not bind to protein A or G, and were present in the high molecular weight fraction of serum; they are clearly IgM antibodies. Further, the antibodies did not react with human ABO blood group substances and are not related to human blood group A or B, which carry a terminal galactose. The reaction of human serum with pig erythrocytes was specifically inhibited by mono- and disaccharides: D-galactose, melibiose, stachyose, methyl-alpha-D-galactopyranoside, and D-galactosamine but not by D-glucose or methyl-beta-D-galactopyranoside; demonstrating that the reaction is with galactose in an alpha and not a beta linkage. A cDNA clone encoding the murine alpha-1,3-galactosyltransferase (which transfers a terminal galactose residue with an (alpha 1-3) linkage to a subterminal galactose) was isolated by polymerase chain reaction (PCR), cloned, and transfected into COS cells, which are of Old World monkey origin and, like humans, do not express Gal(alpha 1-3)Gal. After transfection, COS cells became strongly reactive with human serum and with IB4 lectin [which reacts only with Gal(alpha 1-3)Gal]; this reactivity could be removed by absorption with pig erythrocytes. As most of the antibody reacting with pig cells can be removed by absorption with either melibiose or Gal(alpha 1-3)Gal+ COS cells, most of these react with Gal(alpha 1-3)Gal. These findings provide the basis for genetic manipulation of the pig alpha-1,3-galactosyltransferase for future transplantation studies.

Production and characterization of antibodies to the beta-(1-->6)-galactotetraosyl group and their interaction with arabinogalactan-proteins

Rabbit antisera were raised against beta-(1-->6)-galactotetraose coupled to bovine serum albumin (Gal4-BSA). The antisera reacted with arabinogalactan-proteins (AGPs) isolated from seeds, roots, or leaves of radish (Raphanus sativus L.) as revealed by immunodiffusion analysis. Extensive removal of alpha-L-arabinofuranosyl residues from these AGPs enhanced the formation of precipitin with the antisera. The antisera did not react with such other polysaccharides as soybean arabinan-4-galactan, beta-(1-->4)-galactan, and beta-(1-->3)-galactan, indicating their high specificity toward the consecutive beta-(1-->6)-galactosyl side chains of AGPs. The antibodies were purified by affinity chromatography on a column of immunobilized beta-(1-->6)-galactotetraose as ligand. The specificity of the antibodies toward consecutive (1-->6)-linked beta-galactosyl residues was confirmed by enzyme-linked immunosorbent assay for hapten inhibition against Gal4-BSA as antigen, which revealed that beta-(1-->6)-galactotriose and -tetraose were potent inhibitors, while beta-(1-->3)- or beta-(1-->4)-galactobioses and -trioses were essentially unreactive. Electron-microscopic observation of immunogold-stained tissues demonstrated that AGPs were localized in the middle lamella as well as at the plasma membrane of primary roots of radish. Agglutination of protoplasts prepared from cotyledons occurred with the antibodies, supporting the evidence for localization of AGPs in the plasma membrane. The antibody-mediated agglutination was inhibited by addition of AGPs or beta-(1-->6)-galactotetraose.

Activation of human monocyte chemiluminescence response by acylpoly(1,3)galactosides derived from Klebsiella pneumoniae

The stimulating activity of several preparations isolated from a membrane proteoglycan of a nonencapsulated smooth strain of Klebsiella pneumoniae (Kp-MPG) on the oxidative burst of human blood monocytes was assessed by luminol-enhanced chemiluminescence (CL). Five Kp derivatives were studied: a 34-kd acylpoly(1,3)galactoside (APG), obtained by drastic alkaline hydrolysis and purified by chromatography; an APG preparation subjected to acid hydrolysis that removed the core part and all fatty acids, leaving intact the galactose chain of APG (GC-APG); an APG preparation subjected to mild oxidation (ox APG); a preparation obtained by mild alkaline hydrolysis of Kp-MPG, containing additional ester-linked C14 and C16 fatty acids bound to the APG molecule (EFA-APG); and a polymer of the latter compound, APG pol. EFA-APG directly stimulated monocyte CL, whereas Kp-MPG, APG pol, and the whole bacterial cells had little or no activity. APG itself and ox APG induced a weaker response than EFA-APG. Polymyxin B sulfate completely inhibited the CL response to bacterial lipopolysaccharide (LPS) but not to EFA-APG. The stimulating action of EFA-APG on blood monocytes was dependent on the extracellular levels of both calcium and magnesium. Preincubation of monocytes with monoclonal antibody anti-Mac-1 directed against CD11b, the alpha chain of complement receptor type 3 (CR3; CD11b/CD18), strongly inhibited CL activation by EFA-APG and to a lesser extent CL activation by unopsonized zymosan and rough LPS. Altogether, these findings provide indirect evidence for the contribution of the CD11b/CD18 integrin in the functional interaction of EFA-APG with monocyte membranes. They demonstrate the role of fatty acids in the triggering of monocyte oxidative burst, while the polysaccharide chain itself does not contribute to induction of the CL response in this model. In keeping with the effects of EFA-APG and APG, we show that the monocyte CL response was triggered by bacterial LPS from the rough strain of Salmonella minnesota Re 595 and its lipid A, but not by LPS from smooth strains, again suggesting a critical role for the lipid moiety.

The natural anti-alpha-galactosyl IgG in seminal fluid. A simple means to determine damage to the blood-genital tract barrier in infertile males

A simple method for detecting damage to the blood genital tract barrier (BGTB) is presented. The method is based on the ubiquitous presence of the natural anti-alpha-galactosyl (anti-Gal) IgG antibodies in high titers in the serum of every normal individual, and the interaction between this antibody and alpha-galactosyl residues on rabbit red blood cells (RabRBC). The binding of the anti-Gal antibodies to RabRBC could be demonstrated by the rosetting antiglobulin test. The seminal fluid (SF), normally compartmentalized from the blood, is devoid of anti-Gal reactivity. The SF of a large proportion of infertile males contained significant anti-Gal reactivity, implying transudation of serum IgG molecules probably due to damage in the selective permeability of the BGTB. The diagnostic potential of this assay is discussed.

Binding of a bacterial acylpoly(1,3)galactoside to human blood leucocytes

The binding of a 34-kDa (mol. wt.) acylpoly(1,3)galactoside (APG) extracted from a membrane proteoglycan of Klebsiella pneumoniae to human blood leucocytes was investigated. APG is made of a long poly(1,3)galactose chain, a core-like region and a lipid moiety which comprises two glucosamine residues bound to a phosphate group and two beta OH myristic acids. Fluoresceinated APG was shown to bind preferentially to monocytes and to a lesser extent to polymorphonuclear neutrophils, as determined by flow cytometry. Binding of fluoresceinated APG was inhibited by unlabelled APG; it was concentration dependent, but not saturable, with rapid kinetics. It occurred at +4 degrees C but was markedly increased at 37 degrees C. It involved trypsin-sensitive molecules on the membrane of monocytes. Neither the parent proteoglycan nor lipopolysaccharide from K. pneumoniae or Salmonella minnesota competed for APG binding. A minor non-specific binding to lymphocytes, occurring predominantly on B cells, was observed. Unlike that of lipopolysaccharide, the APG binding was not blocked by polymyxin B sulphate. Interaction between the galactose chain of APG and the galactose receptor does not account for the binding of APG to monocytes because the galactose receptor (Mac-2) is expressed at high density on activated macrophages but not on monocytes. Despite its strong binding to human blood monocytes, APG displayed a much weaker activity than K. pneumoniae membrane proteoglycan with respect to induction of monocyte cytokine synthesis. When administered as a Technetium 99 conjugate, APG was shown to label inflammatory foci in experimental animals, and its property as a marker of macrophages is currently being evaluated in clinical trials.

Rapid isolation of human plasma anti-alpha-galactoside antibody using sugar-specific binding to guar galactomannan or agarose

A method of purifying the naturally occurring antibody to alpha-galactoside moiety (anti-alpha-Gal) in human plasma by a single-step affinity chromatography on cross-linked guar galactomannan (CLGG) or agarose (Sepharose 4B) is described. IgG nature of the two preparations, as revealed by agar gel diffusion, as well as their preference for alpha-anomer of galactose, as revealed in inhibition of their agglutination of trypsinized rabbit erythrocytes by sugars, identified them with anti-alpha-Gal. The antibody binding capacity of Sepharose 4B was only a third of that of CLGG. Both gels showed similar dependence on ionic strength for binding. The pH optimum for binding of anti-alpha-Gal to CLGG was 8.0. Significantly anti-alpha-Gal binding to Sepharose was unaffected by CNBr activation and ligand coupling to the gel, thus warning that contaminating plasma could introduce artifacts in agarose-based chromatography of human tissue biomolecules.

Complement-mediated lysis of Trypanosoma cruzi trypomastigotes by human anti-alpha-galactosyl antibodies

Antibodies that lyse trypomastigotes in a complement-mediated reaction are believed to be the main participants in the protection against virulent Trypanosoma cruzi. Antibodies with a specificity for alpha-galactosyl-containing determinants--generally called antiGal--were studied to determine their role in the lysis of trypomastigote forms. The titers of antiGal markedly increase in Chagas's disease. In the present study we demonstrate binding of this antibody to T. cruzi and the complement-mediated lysis of trypomastigotes by antiGal. Lysis of metacyclic trypomastigotes by whole Chagasic (Ch) serum or isolated antiGal fractions was equally inhibited by alpha- but not by beta-galactosides. Most of the lytic power of the Ch antiGal as well as of the whole Ch serum was removed by absorption on Synsorb-linked Gal alpha 1, 3Gal beta 1, 4GlcNAc followed by rabbit erythrocyte absorption. The Ch antiGal had a lower affinity for melibiose bound to agarose than for the trisaccharide linked to Synsorb, and was several times more effective in the immunolysis of trypomastigotes than the corresponding antiGal from normal human serum. Lytic antibodies were partly absorbed by Serratia marcescens but not by Escherichia coli O111. A human volunteer immunized with an S. marcescens vaccine elicited a specific antiGal response that was lytic to trypomastigotes (70% lysis). We suggest that in vivo high-affinity antiGal antibody clones, as occur in Ch patients, may significantly contribute to the destruction of the parasite, whereas low-affinity antiGal clones are much less effective in the protection against T. cruzi infection.

Antigenic similarities in lipopolysaccharides of Haemophilus and Neisseria and expression of a digalactoside structure also present on human cells

Monoclonal antibodies raised against Haemophilus influenzae and Neisseria gonorrhoeae were used to investigate similarities or differences in the lipopolysaccharide antigens of pathogenic and commensal strains of several Gram-negative bacteria indigenous to mucosal surfaces of humans. In immunoblotting experiments, 20 of 36 monoclonal antibodies showed cross-reactions between species of Neisseria and Haemophilus. The common epitopes were present on N. gonorrhoeae, N. meningitidis, N. lactamica, H. influenzae including biogroup aegyptius, and occasionally H. parainfluenzae. No other commensal Neisseria or Gram-negative organisms tested reacted with the monoclonal antibodies with one exception; a single strain of pathogenic Escherichia coli was recognised by a N. gonorrhoeae-specific monoclonal antibody. One monoclonal antibody, raised against N. gonorrhoeae lipopolysaccharide, reacted with N. gonorrhoeae (32 of 59 strains), N. meningitidis (9 of 26 strains), H. influenzae (6 of 16 strains). An epitope expressed by H. influenzae and implicated in its virulence was also present on 14 of 59 strains of N. gonorrhoeae and was shown to comprise a digalactoside structure, alpha-galactosyl-1,4-beta-galactose (Gal alpha 1,4Gal beta), also found on human cells.