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A subset of human anti-GM1 ganglioside antibodies cross-reacts with Gal(beta 1-3)GalNAc bearing glycoproteins in peripheral nerve and spinal cord. The same oligosaccharide determinant is recognized by the lectin peanut agglutinin (PNA) which binds at the nodes of Ranvier in intact peripheral nerve. The Gal(beta 1-3)GalNAc bearing glycoproteins were isolated using PNA lectin affinity chromatography followed by separation on Western blot, and the proteins were subjected to partial amino acid sequence analysis. Two major PNA binding glycoproteins were identified in peripheral nerve and spinal cord; one had an approximate molecular weight of 120 kD and had sequence homology to the oligodendrocyte-myelin glycoprotein (OMgp). The other migrated between 70 and 80 kD and had sequence homology to the hyaluronate binding domain of versican, which has been reported to share sequence homology with the 70 kD proteins hyaluronectin and the glial hyaluronic acid binding protein (GHAP). By immunocytochemistry, OMgp was localized to the paranodal region of myelin, and the protein homologous to the hyaluronate binding domain of versican was localized to the nodal gap in peripheral nerve. These PNA binding glycoproteins might be target antigens for autoantibodies in peripheral nerve.

We investigated the binding of the gp120 glycoprotein of the human immunodeficiency virus (HIV-1) to neural glycolipids and glycoproteins by ELISA. The gp120 protein bound to sulfatide (GalS), a sulfated glycolipid autoantigen implicated in sensory neuritis, and to the myelin associated glycoprotein (MAG), an autoantigen in demyelinating neuropathy. Binding of gp120 to MAG was inhibited by the HNK-1 antibody, which recognizes a sulfated glucuronic acid epitope, suggesting that the interaction involves carbohydrate determinants. Sulfatide and MAG are potential receptors for gp120 in peripheral nerve and may have a role in the neuropathy associated with HIV-1 infection.

Increased titres of anti-neurofilament antibodies have been reported in neurodegenerative disorders, and it has been suggested that such antibodies might be pathogenic. We investigated the specificity of an IgA monoclonal antibody (MAb) from a patient with amyotrophic lateral sclerosis which reacted with neurofilaments and bound to the surface of neuroblastoma cells. In Western blots, the immunoaffinity-purified IgA bound to the 220-kD, high-molecular-weight neurofilament protein (NFH) and cross-reacted with several closely migrating protein bands with apparent mobility of 62-68 kD in neuroblastoma cells and extracts of normal human spinal cord. Following crosslinking to the surface of radiolabeled neuroblastoma cells, the IgA MAb immunoprecipitated a 65-kD protein, indicating that the protein was present on the cell surface and available to the antibodies for binding. Several other MAbs to NFH did not immunostain the surface of neuroblastoma cells or bind to the 65-kD protein, indicating that the protein was not a fragment of NFH. Thus, antibody binding to the 65-kD protein, possibly by cross-reacting with NFH, may have contributed to the neuronal degeneration.

The HNK-1 carbohydrate epitope, which is shared by several members of the immunoglobulin gene super-family, is also the target epitope for IgM anti-MAG autoantibodies in patients with demyelinating neuropathy. By Western blot analysis, there are 7 HNK-1 immunoreactive glycoproteins in human peripheral nerve myelin, two of which have previously been identified as the myelin associated glycoprotein (MAG) and the P0 glycoprotein. In this study, the remaining HNK-1 bearing glycoprotein bands were characterized by immunoblot and NH2-terminal sequence analysis, and were all identified as degradation products or aggregates of the Po glycoprotein. MAG and P0 are therefore the only HNK-1 bearing glycoproteins in human peripheral nerve myelin.