IMMUNOCHEMICAL AND SEROLOGICAL STUDIES ON THE LIPID HAPTEN OF MYELIN WITH RELATIONSHIP TO EXPERIMENTAL ALLERGIC ENCEPHALOMYELITIS (EAE)

Specificity and cross-reactivity of anti-galactocerebroside antibodies

Anti-galactocerebroside (GalC) antibodies have been reported to inhibit myelin formation, cause demyelination, and block HIV-I infection of neural cells. We examined the binding of 3 monoclonal and polyclonal anti-GalC antibodies to a panel of purified glycolipids by ELISA and by an immunospot assay on nitrocellulose blots. All 3 antibodies bound strongly to GM1 ganglioside, monogalactosyl diglyceride, and asialo-GM1, and 2 of the antibodies bound to GD1b and psychosine. The anti-GalC antibodies also bound to 3 glycoprotein bands in human neuroblastoma cells on Western blot, and binding to the proteins was abolished by pre-treatment with pronase or with periodate which oxidizes the terminal carbohydrate residues. These results indicate that anti-GalC antibodies cross react with oligosaccharide determinants of other glycolipids and glycoproteins, and that these cross-reactivities may be responsible for some of the biological effects of the anti-GalC antibodies.

Novel oligodendrocyte transmembrane signaling systems. Investigations utilizing antibodies as ligands

Antibodies are increasingly being used as tools to study the function of cell surface markers. Several types of responses may occur upon the selective binding of an antibody to an epitope on a receptor. Antibody binding may trigger signals that are normally transduced by endogenous ligands. Moreover, antibody binding may activate normal signals in a manner that disrupts a sequence of events that coordinates either differentiation, mitogenesis, or morphogenesis. Alternately, it is possible that binding elicits either a modified signal or no signal. This article focuses on the cascade of events that occur following specific antibody binding to myelin markers expressed by cultured murine oligodendrocytes. Binding of specific antibodies to the oligodendrocyte membrane surface markers myelin/oligodendrocyte glycoprotein (MOG), myelin/oligodendrocyte specific protein (MOSP), galactocerebroside (GalC), and sulfatide on cultured murine oligodendrocytes results in different effects with regard to phospholipid turnover, Ca2+ influxes, and antibody:marker distribution. The consequence of each antibody-elicited cascade of events appears to be the regulation of the cytoskeleton within the oligodendroglial membrane sheets. The antibody binding studies described in this article demonstrate that these myelin surface markers are capable of transducing signals. Since endogenous ligands for these myelin markers have yet to be identified, it is not known if these signals are normally transduced or are a modification of normally transduced signals.

Production and characterization of high titer antibodies to galactocerebroside

High titer antibodies primarily of the IgG class were produced against galactocerebroside (GalC) by including keyhole limpet hemocyanin (KLH) and supplemental M. tuberculosis in the adjuvant mixture used for immunization of rabbits. Antibody titers were determined by an ELISA in which microtiter wells were coated with liposomes containing lecithin, cholesterol and GalC. The antibodies showed reactivity with GalC and psychosine, but not glucocerebroside, sulfatide, mixed gangliosides or asialo GM1. Specificity was further demonstrated by absorption of antibodies with GalC. Binding was inhibited by galactose, but only at high concentrations. Further, the antibodies did not bind to any brain proteins on immunoblots, indicating lack of reactivity with glycoproteins which might contain a terminal galactose. Antibodies to GalC are directed against different determinants than those reacting with peanut agglutinin since the lectin will not react with GalC, and the antibodies will not react with asialo GM1. The antibodies raised to GalC by this method show specific staining for oligodendroglia in culture. Peanut agglutinin binds intensely to process-bearing GalC+ oligodendroglia, but very poorly to the membrane sheets elaborated by oligodendroglia after longer times in culture. Other process-bearing GalC-, GFAP- cells were also stained with peanut agglutinin; these cells may represent glial precursors.

Lipid content of swine influenza and other vaccines

An analysis of the lipids in swine influenza vaccines was performed, comparing six different lots of swine influenza, other influenza and noninfluenza vaccines. Cholesterol content and phospholipid content varied greatly, but there were no major differences between the types of vaccines. Appreciable amounts of phosphatidylethanolamine were found in only one swine influenza vaccine. The major phospholipids of influenza vaccines were phosphatidylcholine, sphingomyelin and phosphatidic acid. A detectable amount of phosphatidylserine was not found in any swine influenza vaccine, but was present in two of three nonswine influenza vaccines. Only two of six swine influenza vaccines showed trace amounts (less than 0.5 microgram/ml) of ganglioside (GM3). However, larger quantities of galactocerebroside were found (2.24-6.43 micrograms/ml) in all influenza vaccines examined, including swine influenza vaccines.

Transient expression of glial fibrillary acidic protein in developing oligodendrocytes in vitro

Expression of galactocerebroside (GC) and glial fibrillary acidic protein (GFAP) was studied in oligodendrocyte-enriched cultures of newborn mouse brains. In the cultures, GC was detectable as early as 1 day in vitro (1-DIV). Using double immunofluorescence labeling, some GC-positive cells were also stained homogeneously by the anti-GFAP serum. The intensity of GFAP staining increased until 9-DIV when the GC-positive cells revealed the typical morphology of oligodendrocytes, and the GFAP staining faded thereafter. The GFAP staining pattern of the GC-positive cells was not changed upon exposure to demecolcine, even though the GC-negative, GFAP-positive astrocytes showed perinuclear aggregation of GFAP. No intermediate filaments were observed in the oligodendrocytes by electron microscopy. The results suggest that the oligodendrocytes may have soluble GFAP in a certain period of early development.

Central nervous system lipid alterations in rats with experimental allergic encephalomyelitis and its suppression by immunosuppressive drugs

Rats with experimental allergic encephalomyelitis (EAE) induced with myelin or spinal cord show decreases in the content of sulphatides and cerebrosides and increases in the level of esterified cholesterol in the CNS. In this work it is shown that brain sulphatide changes can be obtained by injection of mixtures containing glycosphingolipids. Alterations in the content of cerebrosides occur when the injection mixture contains cerebrosides. The alterations of sulphatides and cholesterol ester induced by injection of spinal cord could be suppressed by treatment with immunosuppressive drugs (dexamethasone, cyclophosphamide and 6-mercaptopurine) able to prevent clinical signs of EAE.

Effector--target cell interaction of lymph node cells from galactocerebroside-sensitized rats with oligodendrocytes of brain cell cultures

Inbred Lewis rats were sensitized with galactocerebrosides (GC) and hemocyanin. After 10 years lymph node cells (LNC) depleted of phagocytic cells were obtained. These cells were tested on mixed brain cell cultures enriched with GC-positive oligodendrocytes. Within 3--48 h of incubation, conjugate formation between LNC and oligodendrocytes was observed. Interaction of effector cells with their target resulted in defective oligodendrocytes. Anti-GC-LNC did not adhere to or lyse astrocytes or fibroblasts. Control LNC from rats sensitized only with the carrier protein did not interact with oligodendrocytes.

Experimental allergic neuritis induced by galactocerebroside

Experimental allergic neuritis (EAN), an animal model of human demyelinative neuritis, was induced by sensitization with galactocerebroside, a glycolipid hapten common in central and peripheral nervous system myelin. Between two months and one year after the initial sensitization, 11 of 24 rabbits immunized repeatedly with bovine brain galactocerebroside (GC) in complete Freund's adjuvant developed a neurological disorder manifested by flaccid quadriparesis, limb hypesthesia, and respiratory paralysis. Seventeen of 20 autopsied rabbits, including all those with clinical illness, had small multiple perivascular foci of demyelinative lesions in roots, dorsal root ganglia, proximal peripheral nerves adjacent to ganglia, and, less frequently, in distal nerves. No change was found in the central nervous system. Demyelination started around venules, with splitting and vesiculation of the outer myelin sheaths of adjacent fibers, and later progressed to form confluent lesions. The lesions were associated with infiltration of phagocytic mononuclear cells, mostly macrophages, which insinuated themselves between myelin lamellae, phagocytized myelin, and subsequently denuded axons. Perivenular infiltration of small lymphocytes, comparable to that seen in whole nerve- induced EAN, was not encountered. The distribution of demyelinative lesions seems to correspond to areas known to have a defective blood-nerve barrier.

EAE, EAN and galactocerebroside sera bind to oligodendrocytes and Schwann cells

Sera from rabbits with EAN induced by sensitization with galactocerebroside (GalC-EAN) bound to the surface of Schwann cells and oligodendrocytes in rat nervous system dispersion cultures. Sera from rabbits with bovine femoral nerve-induced EAN (FN-EAN) bound to Schwann cells, oligodendroglia and occasional fibroblasts. Sera from animals with bovine spinal cord-induced EAE (SC-EAE) bound to these cells and to some astrocytes as well. Absorption of the capacity to bind to oligodendroglia and Schwann cells suggests that GalC is the major, if not the only surface antigen on these two cell types to which these sera bind. The capacity of GalC-EAN, SC-EAE, and FN-EAN sera to bind to the surface of the cells responsible for myelin synthesis in both PNS and CNS correlates with the ability of these sera to cause both PNS and CNS demyelination in vitro and PNS demyelination in vivo.

Antiserum induced myelination inhibition in vitro without complement

Exposure of neonatal rat cerebellum cultures to antiserum to whole spinal cord or galactocerebroside inhibited myelin formation regardless of whether guinea pig serum was added fresh or after heating to 56 degrees C for 1 h in order to achieve complete removal of hemolytic complement activity. Myelination followed removal of antisera from the culture media. This suggests that the inhibition of primary myelination by anti-CNS tissue antiserum occurs through some mechanism other than as the result of a cytotoxic reaction against oligodendrocytes mediated via the complement system.

Cell-type-specific markers for distinguishing and studying neurons and the major classes of glial cells in culture

We have used 4 cell-type-specific markers to identify individual glial and neuronal cells in dissociated cell cultures of neonatal rat sciatic nerve, dorsal root ganglia (DRG), optic nerve, cerebellum, corpus callosum, cerebral cortex and leptomeninges. Schwann cells were identified with antibodies against rat neural antigen-1 (Ran-1), neurons with tetanus toxin, astrocytes with antibody against the glial fibrillary acidic protein (GFAP) and oligodendrocytes with antibody against galactocerebroside. All of these ligands react with cell surface molecules except for anti-GFAP antibody which binds to intracellular glial filaments. Using two-fluorochrome immunofluorescence we have studied the distribution of various glycoproteins and glycolipids on these 4 major neural cell types in short-term cultures. We have found that (1) although Ran-1 is expressed on glial and neuronal tumours, it was not found on normal astrocytes, oligodendrocytes or neurons; (2) Thy-1 was present on fibroblasts and some neurons but not on the majority of leptomeningeal cells or on oligodendrocytes or astrocytes in short-term cultures (however, it was expressed on some astrocytes in longer term cultures); (3) the 'large external transformation sensitive' (LETS) protein could be detected on fibroblasts and leptomeningeal cells but not on neurons or glial cells; (4) GM1 was present on all neurons, most oligodendrocytes and approx. 50% of other cell types; sulfatide and GM3 were only detectable on oligodendrocytes, while globoside was only found on some neurons. In addition, we were able to identify putative microglial cells by the presence of cell surface receptors for IgG and by their phagocytic activity; they did not express and of the cell-type-specific defining markers.

Demyelination produced by experimental allergic neuritis serum and anti-galactocerebroside antiserum in CNS cultures. An ultrastructural study

Cultures of mouse cerebellum were exposed to sera from rabbits with experimental allergic neuritis induced by whole peripheral nerve immunization (WN-EAN) and to rabbit anti-galactocerebroside (GC) antisera, and were studied by electron microscopy. Both antisera produced almost identical demyelinative patterns. These consisted of large intramyelinic splittings, "smudged" changes of myelin, degeneration of oligodendrocytes, and phagocytosis of myelin by astrocytes, changes similar to those described after application of whole spinal cord-induced experimental allergic encephalomyelitis (WM-EAE) sera. In addition, patterns which have been considered more characteristic of in vivo demyelinative lesions have been found, susch as vesicular disruption of myelin lamellae and peeling off and phagocytosis of myelin by phagocytic mononuclear cells with electron dense cytoplasm. The morphologic similarities between demyelinative patterns in central nervous system (CNS) cultures induced by anti-GC antiserum and WN-EAN serum and WM-EAE serum, and the fact that elevated antibody titers to GC are found in sera from rabbits with WN-EAN and WM-EAE (Saida, et al., 1977), support the concept that anti-GC antibody is the major factor in the production of CNS demyelination in vitro by sera from rabbits with WN-EAN and WN-EAE.

Antibodies to galactocerebroside bind to oligodendroglia in suspension culture

Antisera raised in rabbits against galactocerebroside bind to bovine oligodendroglia in suspension in significant titer as demonstrated by indirect immunofluorescence. Absorption of antigalactocerebroside antiserum with galactocerebroside, oligodendroglia, or myelin markedly reduces the antigalactocerebroside antibody titer as measured by a radioimmunoprecipitation test as well as the binding to oligodendroglia. Incubation with some other galactose-containing glycolipids results in a parallel decrease in binding to oligodendroglia and reduction in antigalactocerebroside antibody titer. Antigalactocerebroside antibodies provide a useful and specific tool with which to study development of oligodendroglia and myelin as well as immunopathologic mechanisms which might be involved in demyelinating diseases.

Serological techniques for detection of antibody to galactocerebroside

Two serological techniques were developed for the detection of antibody to galactocerebroside using liposomes as a carrier for the lipid hapten. One assay is a radioimmunoprecipitation test employing [3H] cholesterol as a marker in the galactocerebroside-liposomes. The other is a less sensitive but quick and easy galactocerebroside-liposome agglutination assay. Specificity is demonstrated by comparison of titers when other lipid haptens replace galactocerebroside in the liposomes, and when other anti-glycolipid antisera are reacted with galactocerebroside-liposomes.

Effect of 5-bromo-2'-deoxyuridine or cytosine-B-D-arabinofuranoside hydrochloride on myelination in newborn rat cerebellum cultures following removal of myelination inhibiting antiserum to whole cord or cerebroside

Myelination was inhibited in cultures of newborn rat cerebellum by exposure to antisera prepared by injecting rabbits with whole guinea pig spinal cord or cerebrosixde mixed with bovine serum albumin. At 15 days in vitro (DIV), when 90-100% of our control cultures were myelinated, antiserum inhibited cultures were washed and refed routine culture medium or medium containing 5-bromo-2'-deoxyuridine (BUdR) or cytosine-B-D-arabinofuranoside hydrochloride (ara-C) in concentrations previously shown to inhibit myelination in our system. The disinhibited cultures myelinated within 2-5 days of removal of antiserum regardless of the presence of BUdR or ara-C. The evidence suggests that the myelin-forming oligodendrocytes do not undergo cell division before myelination during disinhibition from antiserum. In addition, cultures exposed to BUdR on 5-7 DIV in the presence of antiserum and disinhibited at 10 DIV did not have myelinated axons as observed by light microscopy at 15 DIV. Thus, the BUdR sensitive oligodendrocyte division remained intact in antiserum inhibited cultures. We conclude that the antisera inhibit myelin formation without interrupting the pattern of cell division or the covert differentiation of oligodendrocytes.