Generation and characterization of antibodies to sulfated glucuronyl glycolipids in Lewis rats

Selective in vivo removal of pathogenic anti-MAG autoantibodies, an antigen-specific treatment option for anti-MAG neuropathy

Anti-MAG (myelin-associated glycoprotein) neuropathy is a disabling autoimmune peripheral neuropathy caused by monoclonal IgM autoantibodies that recognize the carbohydrate epitope HNK-1 (human natural killer-1). This glycoepitope is highly expressed on adhesion molecules, such as MAG, present in myelinated nerve fibers. Because the pathogenicity and demyelinating properties of anti-MAG autoantibodies are well established, current treatments are aimed at reducing autoantibody levels. However, current therapies are primarily immunosuppressive and lack selectivity and efficacy. We therefore hypothesized that a significant improvement in the disease condition could be achieved by selectively neutralizing the pathogenic anti-MAG antibodies with carbohydrate-based ligands mimicking the natural HNK-1 glycoepitope 1. In an inhibition assay, a mimetic (2, mimHNK-1) of the natural HNK-1 epitope blocked the interaction of MAG with pathogenic IgM antibodies from patient sera but with only micromolar affinity. Therefore, considering the multivalent nature of the MAG-IgM interaction, polylysine polymers of different sizes were substituted with mimetic 2. With the most promising polylysine glycopolymer PL₈₄(mimHNK-1)₄₅ the inhibitory effect on patient sera could be improved by a factor of up to 230,000 per epitope, consequently leading to a low-nanomolar inhibitory potency. Because clinical studies indicate a correlation between the reduction of anti-MAG IgM levels and clinical improvement, an immunological surrogate mouse model for anti-MAG neuropathy producing high levels of anti-MAG IgM was developed. The observed efficient removal of these antibodies with the glycopolymer PL₈₄(mimHNK-1)₄₅ represents an important step toward an antigen-specific therapy for anti-MAG neuropathy.

Induction of experimental ataxic sensory neuronopathy in cats by immunization with purified SGPG

IgM paraproteins in about 50% of the patients with neuropathy associated with IgM gammopathy react with carbohydrate moieties in myelin-associated glycoprotein (MAG) and in sulfated glucuronic glycolipids (SGGLs) in human peripheral nerves. However, the role of anti-MAG/SGGL antibodies in the pathogenesis of neuropathy remains unclear. In order to induce an animal model of neuropathy associated with anti-MAG/SGGL antibodies, cats were immunized with sulfoglucuronyl paragloboside (SGPG). All four cats immunized with SGPG developed clinical signs of sensory neuronopathy within 11 months after initial immunization, characterized by unsteadiness, falling, hind limb weakness and ataxia. In two cats the ataxia and hind limb paralysis were so severe that the animals had to be euthanized. Pathological examination revealed sensory ganglionitis with inflammatory infiltrates in the dorsal root ganglia. No overt signs of pathology were noted in the examined roots or nerves. High titer anti-SGPG/MAG antibodies were detected in all 4 cats immunized with SGPG but not in 3 control cats. Our data demonstrate that immunization of cats with SGPG induced anti-SGPG antibodies and sensory neuronopathy clinically resembling the sensory ataxia of patients with monoclonal IgM anti-MAG/SGPG antibodies. This study suggests that these anti-MAG/SGPG antibodies play a role in the pathogenesis of this neuropathy.

Lewis rats immunized with GM1 ganglioside do not develop peripheral neuropathy

Elevated levels of anti-GM1 antibodies are associated with motor nerve syndromes. Although there is a lot of circumstantial evidence that anti-GM1 antibodies may be causing the disease, their precise role remains unclear. In order to study the role of anti-GM1 antibodies in the pathogenesis of peripheral neuropathy, eight Lewis rats were injected with GM1 ganglioside mixed with keyhole limpet hemocyanin (KLH) and emulsified with Freund's adjuvant and three rats were immunized with GM1 in liposomes. Although IgM class anti-GM1 antibodies were detected in all animals immunized with GM1, none of the animals exhibited overt signs of neuropathy during 6 months after initial immunization. IgG antibody to GM1 was not produced in any of the animals. There was no pathological evidence of nerve damage. These studies suggest that elevated levels of IgM anti-GM1 antibodies by themselves do not cause nerve damage in rats.

A novel Gal(beta1-4)Gal(beta1-4)Fuc(alpha1-6)-core modification attached to the proximal N-acetylglucosamine of keyhole limpet haemocyanin (KLH) N-glycans

KLH (keyhole limpet haemocyanin), the oxygen-carrying molecule of the marine snail Megathura crenulata, is often used as an adjuvant or as a hapten carrier for immunizations with peptides, oligosaccharides or other low-molecular-mass organic compounds. KLH exhibits several carbohydrate determinants, at least some of which are immunogenic: it shares an antigenic Fuc(alpha1-3)GalNAc-determinant with schistosomes and contains unique Gal-(beta1-6)Man-structural motifs on its N-glycans. This study reveals the presence of N-glycans with unusual +/-Gal(beta1-4)Gal(beta1-4)Fuc- units (alpha1-6)-linked to the reducing end N -acetylglucosamine residue. The following novel structures of KLH N-glycans were deduced by linkage analysis, exoglycosidase digestion, matrix-assisted laser-desorption ionization-tandem MS and nano-LC-ESI-IT-MS (where LC stands for liquid chromatography, ESI for electrospray ionization and IT for ion trap): Man(alpha1-6)[+/-Man(alpha1-3)]Man(beta1-4)GlcNAc(beta1-4)[Gal(beta1-4)Fuc(alpha1-6)]GlcNAc and Man(alpha1-6)Man(beta1-4)GlcNAc(beta1-4)[Gal(beta1-4)Gal(beta1-4)Fuc(alpha1-6)]GlcNAc. The Gal(beta1-4)Fuc- and Gal(beta1-4)Gal(beta1-4)Fuc- core modifications are expected to be immunogenic, similar to other non-mammalian-type core modifications, and to contribute to the immunostimulatory properties of KLH.