Mild encephalitogenic activity of basic protein--acidic lipid complex from myelin and detection of immune complexes in experimental allergic encephalomyelitis

Complement and Humoral Adaptive Immunity in the Human Choroid Plexus: Roles for Stromal Concretions, Basement Membranes, and Epithelium

The choroid plexus (CP) provides a barrier to entry of toxic molecules from the blood into the brain and transports vital molecules into the cerebrospinal fluid. While a great deal is known about CP physiology, relatively little is known about its immunology. Here, we show immunohistochemical data that help define the role of the CP in innate and adaptive humoral immunity. The results show that complement, in the form of C1q, C3d, C9, or C9neo, is preferentially deposited in stromal concretions. In contrast, immunoglobulin (Ig) G (IgG) and IgA are more often found in CP epithelial cells, and IgM is found in either locale. C4d, IgD, and IgE are rarely, if ever, seen in the CP. In multiple sclerosis CP, basement membrane C9 or stromal IgA patterns were common but were not specific for the disease. These findings indicate that the CP may orchestrate the clearance of complement, particularly by deposition in its concretions, IgA and IgG preferentially via its epithelium, and IgM by either mechanism.

Concerted modulation by myelin basic protein and sulfatide of the activity of phospholipase A2 against phospholipid monolayers

The effect of myelin basic protein (MBP) on the activity of phospholipase A2 (PLA2, EC 3.1.1.4) against monolayers of dilauroylphosphatidylcholine (dlPC) or dilauroylphosphatidic acid (dlPA) containing different proportions of sulfatide (Sulf) and galactocerebroside (GalCer) was investigated. MBP was introduced into the interface by direct spreading as an initial constitutive component of the lipid-protein film or by adsorption and penetration from the subphase into the preformed lipid monolayers. The effect of MBP on PLA2 activity depends on the type of phospholipid and on the proportion of MBP at the interface. At a low mole fraction of MBP, homogeneously mixed lipid-protein monolayers are formed, and the PLA2 activity against dlPC is only slightly modified while the degradation of dlPA is markedly inhibited. This is probably due to favorable charge-charge interactions between dlPA and MBP that interfere with the enzyme action. The PLA2 activity against either phospholipid is increased when the mole fraction of MBP exceeds the proportion at which immiscible surface domains are formed. GalCer has little effect on the modulation by MBP of the phospholipase activity. The effect of Sulf depends on its proportions in relation to MBP. The individual effects of both components balance each other, and a finely tuned modulation is regulated by the interactions of MBP with Sulf or with the phospholipid.

Anti-lymphocyte antibodies and circulating immune complexes in the sera of patients with myelopathy associated with human T lymphotropic virus type-I

We measured levels of circulating immune complexes in the human T-lymphotropic virus type I (HTLV-I)-associated myelopathy (HAM) by Raji cell assay and C1q binding assay using an enzyme-linked immunosorbent assay (ELISA). The levels of anti-lymphocyte antibody were also measured using normal donor peripheral blood T-lymphocytes. The levels of anti-lymphocyte antibodies were significantly higher in the sera of patients with HAM compared to controls (P < 0.01). The concentrations of immune complexes measured by Raji cell assay were also significantly higher in the HAM patients' sera than in controls. However, when levels of immune complexes were measured by C1q binding assay, there was no significant difference between HAM patients and controls. There was no significant difference in the levels of anti-lymphocyte antibodies and immune complexes between HTLV-I carriers and controls. Circulating immune complexes detected by the Raji cell assay did not include HTLV-I p-19 as detected by the indirect immunofluorescent method. Levels of anti-lymphocyte antibody were correlated with levels of circulating immune complexes as detected by the Raji cell assay in the sera of patients with HAM. These findings indicate that anti-lymphocyte antibodies and circulating immune complexes are present in the sera of HAM patients, and that the levels of complexes detected by Raji cell assay may reflect anti-lymphocyte antibody levels.

Interaction and fusion of unilamellar vesicles containing cerebrosides and sulfatides induced by myelin basic protein

The effects of myelin basic protein on the aggregation, lipid bilayer merging, intercommunication of aqueous compartments and leakage of small unilamellar vesicles of egg phosphatidylcholine containing different proportions of galactocerebroside and sulfatide were investigated. This was performed employing light scattering, absorbance changes and fluorescence assays (resonance energy transfer, Terbium/dipicolinic acid assay and carboxyfluorescein release). The apposition of membranes rapidly induced by myelin basic protein is enhanced by sulfatide but reduced by galactocerebroside compared to vesicles of egg phosphatidylcholine alone. On the other hand, the presence of either glycosphingolipid in the membrane interferes with the induction by myelin basic protein of lipid bilayer merging, subsequent fusion and changes of the membrane permeability. Our results support an important modulation by sulfatide and galactocerebroside on the interactions among membranes induced by myelin basic protein, depending on the relative proportions of the glycosphingolipids and phosphatidylcholine.

The astroglial response to autonomic tissue grafts

Autonomic (superior cervical) ganglia were grafted either into the IV ventricle where minimal trauma occurred or directly into the cerebral cortex which was necessarily traumatic. Previous studies have shown that host astroglia may migrate into autonomic tissue grafts. The purpose of the present study was to compare and contrast the astroglial response in allo- and autografts. By monitoring the host response in the two model sites using glial fibrillary acidic protein (GFAP) immunostaining in 1 micron plastic sections we sought to determine the role of injury stimulus in astroglial migration. In addition, these models could be used to investigate any potential differences in glial reactivity produced by allo- or autograft antigenic stimulation. In both ventricular and parenchymal locations, astroglia migrated progressively into allografts. Migration, which could have taken place along anastomotic vascular connections, began after one week and was continual, eventually replacing graft neural tissue. Astrocytic processes appeared enlarged and highly immunoreactive only as they entered the allografts or were in close association with the choroid plexus; adjacent host astrocytes were unaltered. Glial migration was greatly reduced in ventricular autografts but in the parenchymal site was nearly comparable to that of allografts. It was suggested that certain immunological factors may be involved in glial reactivity or migration considering the observed differences in the non-traumatic model whereas tissue damage stimulus played a major role in migration in both allo- and autografts. In no instances were typical astrocytic end-feet found on the autonomic graft vessels. The host astrocytic response to grafted autonomic tissue occurred significantly later (5-7 days) than the host endothelial response. This observation indicates that the graft vessels were original, intrinsic ones and the astrocytic invasion played no role in influencing endothelium with regards to brain-barrier properties.

Anti-endothelial cell antibody and immune complexes in the sera of animals with acute experimental allergic encephalomyelitis and chronic relapsing experimental allergic encephalomyelitis

Blood-brain barrier (BBB) injury occurs in both acute and chronic relapsing experimental allergic encephalomyelitis (EAE). Sera from animals in which these forms of EAE had been induced were examined for anti-endothelial cell antibodies and immune complexes by enzyme-linked immunosorbent assay (ELISA) using either cultured endothelial cells or Raji cells. IgG binding to endothelial cells was significantly increased in the sera of animals with acute EAE and chronic relapsing EAE, compared to controls. Increased levels of circulating immune complexes were also detected in the sera of some animals with chronic relapsing EAE, especially those in an exacerbation. It is suggested that the anti-endothelial cell antibody and immune complexes detected may play pathogenetic roles in the destruction of the BBB in EAE.

Further evidence for an intrinsic neuraminidase in CNS myelin

An intrinsic neuraminidase activity in rat brain CNS myelin has been demonstrated and compared with the neuraminidase activity in rat brain microsomes. With use of ganglioside GM3 as a substrate, the myelin-associated neuraminidase exhibited a shallow pH curve with an optimum at pH 4.8 whereas the microsomal activity had a marked optimum at pH 4-4.3. Neuraminidase activity in both fractions was optimized in 0.3% Triton CF-54 but activation was much greater in the microsomes. When the neuraminidase activities were examined at 60 degrees C, the myelin neuraminidase activity was more than sevenfold of that observed at 37 degrees C and was linear for at least 2 h; the microsomal activity increased only fivefold initially and exhibited a continual loss in activity. Addition of excess microsomes to the total homogenate prior to myelin isolation resulted in no change in myelin neuraminidase activity. When the two membrane fractions were examined at equivalent protein concentrations in the presence of additional cations or EDTA (1 mM), similar but not identical effects on neuraminidase activity were seen. The microsomal neuraminidase was considerably more susceptible to inhibition by divalent copper ion. Activity in both fractions was markedly inhibited by Hg2+ and Ag+ whereas EDTA had no effect on either activity. The myelin-associated neuraminidase activity was the highest in cerebral hemispheres, followed by brainstem, cerebellum, and spinal cord and was extremely low in sciatic nerve. In fact, the myelin neuraminidase activity was higher than the microsomal enzyme activity in the cerebral hemispheres.(ABSTRACT TRUNCATED AT 250 WORDS)

Similarities between the Forssman carotid syndrome and experimental allergic encephalomyelitis

The Forssman carotid syndrome was induced in guinea pigs to study the mechanism of demyelination-like lesions in this animal model and to compare it with experimental allergic encephalomyelitis days after intracarotid injection of rabbit anti-Forssman antibody and chronic lesions at 7-21 days post injection, using routine histological, immunofluorescent, and electron-microscopic techniques. The results were compared to those in a group of guinea pigs with acute or chronic lesions of EAE. The picture was remarkably similar in the two conditions, in regard to localization in the central nervous system (CNS), composition of cellular infiltrates, diameter of lesions produced, myelin loss and axonal degeneration, together with gamma globulin deposition in small vessels in affected areas. The differences were that in the Forssman carotid syndrome, in contrast to EAE, there were no mononuclear cell infiltrates in the acute phase, and no evidence of macrophages invading myelin sheaths was detected. Perivascular lesions consisted of demyelination within infiltrates of mono-nuclear cell in chronic relapsing EAE, but not in the Forssman carotid syndrome. It is suggested that investigation of the CNS may be of benefit in the pathogenetic study of demyelinating disease.

Detection of immune complexes in experimental allergic neuritis

Circulating immune complexes were assayed in the sera of animals with experimental allergic neuritis (EAN), and immunofluorescent staining and immunohistological examination were performed to clarify the role of immune complexes in the pathogenesis of EAN. The level of immune complexes in the sera of animals with clinical signs of EAN was from 1:32 to 1:64. Control animals showed a titer of immune complexes from 1:2 to 1:4. Animals with EAN showed deposition of immune complexes, which were detected by FITC-conjugated anti-rat IgG or C3-complement, in the vessels of the peripheral nerve. These findings suggest that immune complexes may contribute to the immunopathogenesis of EAN.

Interaction of ganglioside GM1 and myelin basic protein studied by carbon-13 and proton nuclear magnetic resonance spectroscopy

The interaction of the myelin basic protein (MBP) and the major endogenous ganglioside GM1 in myelin of the central nervous system has been investigated using both 500-MHz 1H and 67.89 MHz 13C NMR. Titration of MBP by GM1 resulted in 13C NMR signal shifts for the I1e and His residues of MBP at a GM1/MBP mole ratio of one or less. The carbohydrate head group of GM1 was also found to be perturbed. 1H NMR results obtained in a similar manner demonstrated the perturbation of His and Phe residues. At a GM1/MBP mole ratio of 0.5, small perturbation of Trp #116 was observed, and at mole ratios of two and beyond significant involvement of Phe residues and methylated Arg #107 was found. Met #167 was more perturbed than Met #20; hence, more extensive interaction of the lipid is occurring with the C-terminus of the protein than with the N-terminus. No resonances from GM1 bound to MBP at mole ratios of up to one appeared in the spectra. However, as the GM1/MBP mole ratio was increased to eight or greater a major conformational change of MBP was detected. An upfield shift of the GM1 midchain methylene resonance was observed for the GM1/MBP complex. This observation provides strong evidence that the state of GM1 interacting with MBP is different from that of GM1 micelles. The number of saturable GM1 binding sites on MBP is estimated to be four. The data also favor a rapid exchange between bound GM1 and GM1 micelles. Interaction of MBP with the oligosaccharide derived from GM1 was found to be weaker than with GM1. Based on our data, a model for the interaction can be proposed: the first GM1 molecule is bound to the protein molecule through its head group and hydrocarbon chains, followed by the formation of a GM1/MBP complex with a concomitant conformational change of MBP as more GM1 is added.

Myelin basic protein: a component of circulating immune complexes in multiple sclerosis

Myelin basic protein (MBP) is an antigenic component of circulating immune complexes (CIC) in patients with multiple sclerosis (MS). Immune complexes were isolated from the sera by adsorption to Raji cells and then acid eluted. Final identification of MBP from Raji eluates was done by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by MBP radioimmunoassay (RIA) of gel eluates and by an immunoblot technique.

Chronic neuropathy associated with immune complexes of hepatitis B virus

In 7 patients, including one autopsied case, with neuropathy associated with hepatitis B virus infection, histologic examination of sural nerve biopsies revealed small vessel vasculitis in the vasa nervorum. In all cases, immunofluorescent deposits of hepatitis B surface antigen, immunoglobulin and C3 complement were detected in the vasa nervorum. That these deposits could represent immune complexes composed of hepatitis B virus was supported by the serologic demonstration of high serum-level of immune complexes and by the ultrastructural demonstration of electron-dense deposits around the endoneural capillary and in the endoneurium. The densities of large myelinated fibers were significantly lower than controls (P less than 0.01) in 6 of 7 cases. These results suggest that immune complexes composed of hepatitis B virus might play a significant role in the pathogenesis of endoneural and epineural vascular lesions, through which neuropathy may be induced in patients with hepatitis B virus infection.

Ganglioside-basic protein interaction: protection of gangliosides against neuraminidase action

The ability of acidic phospho- and sphingolipids to interact with basic proteins was studied by double diffusion analysis. The phospholipids, tri- and diphosphoinositide, and the sphingolipid, sulfatide, interacted with myelin basic protein as evidenced by precipitin line formation. Of the sialoglycosphingolipids (gangliosides) tested, only the myelin-specific monosialoganglioside, GM4, formed a precipitin line with myelin basic protein. In addition, myelin basic protein retarded the activity of Clostridium perfringens neuraminidase against GM4 and the disialoganglioside, GD1b. Examination of purified rat brain myelin suggested the presence of a neuraminidase activity intrinsic to myelin. This finding, in concert with ganglioside-myelin basic protein complexes which selectively protect against neuraminidase, may provide a physiological explanation for the simplified ganglioside pattern found in myelin.

Gangliosides and proteins in developing chicken brain myelin

Ganglioside and protein content of chicken brain myelin have been studied as a function of development and maturation. Ganglioside concentration remained relatively constant at approximately 225-266 micrograms sialic acid per 100 mg myelin, from 17-day-old embryos to 540-day-old adults. The ganglioside distributional pattern was also constant, GM1 and GM4 each accounting for approximately one-third of total sialic acid. These properties are contrasted with those of mouse and rat brain myelin which previously showed enrichment of GM1 at early stages of myelination and appearance of GM4 at a later stage of maturation. In an earlier study of the mouse total myelin gangliosides doubled in concentration between 3 and 5 weeks of age and full maturity. Myelin proteins of the chicken also remained relatively constant in concentration and distributional pattern during development, although the percentage of basic protein increased somewhat during the first few weeks after hatching. Correlations were observed between molar concentrations of basic protein and various gangliosides, particularly the monosialo types.

Preparation of anti-GM4 antiserum and its assay by a solid-phase radioimmunoassay

Anti-GM4 antiserum was prepared from rabbits by immunization with pure human brain GM4 ganglioside in complete Freund's adjuvant and methylated bovine serum albumin. None of the immunized animals developed any clinically apparent neurological dysfunction. The antiserum titer and specificity were analyzed by double immunodiffusion and a novel solid-phase radioimmunoassay (RIA). In the latter procedure, microtiter plate wells were coated first with the glycolipid antigen, followed by sequential application of antiserum and [125I]-Staphylococcal Protein A. The absorbed radioactivity in the well was then counted. Employing the RIA procedure, anti-GM4 antibody achieved a titer of 1:1600. The antiserum also exhibited a high degree of specificity to GM4; cross-reactivity with glycolipids of similar structure was negligible. The production of highly specific antiserum to GM4 and the feasibility of detecting antibodies to glycolipid antigens by a convenient solid-phase RIA should be useful to further study the biological and immunological roles of GM4 and other glycolipids in the central nervous system.