Enzyme-linked immunoadsorbent assays for myelin basic protein and antibodies to myelin basic protein

An in vivo accelerated developmental myelination model for testing promyelinating therapeutics

Background

Therapeutic agents stimulating the process of myelination could be beneficial for the treatment of demyelinating diseases, such as multiple sclerosis. The efficient translation of compounds promoting myelination in vitro to efficacy in vivo is inherently time-consuming and expensive. Thyroid hormones accelerate the differentiation and maturation of oligodendrocytes, thereby promoting myelination. Systemic administration of the thyroid hormone thyroxine (T4) accelerates brain maturation, including myelination, during early postnatal development. The objective of this study was to validate an animal model for rapid testing of promyelinating therapeutic candidates for their effects on early postnatal development by using T4 as a reference compound.

Methods

Daily subcutaneous injections of T4 were given to Sprague Dawley rat pups from postnatal day (PND) 2 to PND10. Changes in white matter were determined at PND10 using diffusion tensor magnetic resonance imaging (DTI). Temporal changes in myelination from PND3 to PND11 were also assessed by quantifying myelin basic protein (MBP) expression levels in the brain using the resonance Raman spectroscopy/enzyme-linked immunosorbent assay (RRS-ELISA) and quantitative immunohistochemistry.

Results

DTI of white matter tracts showed significantly higher fractional anisotropy in the internal capsule of T4-treated rat pups. The distribution of total FA values in the forebrain was significantly shifted towards higher values in the T4-treated group, suggesting increased myelination. In vivo imaging data were supported by in vitro observations, as T4 administration significantly potentiated the developmental increase in MBP levels in brain lysates starting from PND8. MBP levels in the brain of animals that received treatment for 9 days correlated with the FA metric determined in the same pups in vivo a day earlier. Furthermore, accelerated developmental myelination following T4 administration was confirmed by immunohistochemical staining for MBP in coronal brain sections of treated rat pups.

Conclusions

T4-treated rat pups had increased MBP expression levels and higher MRI fractional anisotropy values, both indications of accelerated myelination. This simple developmental myelination model affords a rapid test of promyelinating activity in vivo within several days, which could facilitate in vivo prescreening of candidate therapeutic compounds for developmental hypomyelinating diseases. Further research will be necessary to assess the utility of this platform for screening promyelination compounds in more complex demyelination disease models, such us multiple sclerosis.

Supplementary information

The online version contains supplementary material available at 10.1186/s12868-022-00714-y.

Sequence determinants of modified cobra venom neurotoxin which induce immune resistance to experimental allergic encephalomyelitis: molecular mechanisms for immunologic action

A nontoxic, iodoacetamide-modified cobratoxin derivative (CAM-NTX) induced resistance to experimental allergic encephalomyelitis (EAE) in guinea pigs. Resistance was retained after trypsin digestion and shown to reside in N-terminal and central peptides of CAM-NTX. A similarly modified protein cardiotoxin (CAM-CTX), representative of proteins homologous with cobratoxin, was not immunosuppressive. Depressed clinical symptoms in EAE-resistant animals correlated with reduced lymphocytic infiltration of the brain. Antibody to myelin basic protein (MBP) was reduced in immunosuppressed animals. The immunoinhibitory determinants in CAM-NTX may mimic immune response suppressor proteins (SIRS-alpha 7) and the EAE-resistance region of MBP.

Enzyme immunoassay for myelin basic protein in cerebrospinal fluid

Myelin basic proteins (MBPs) are a set of proteins making up about 30% of the protein content of the central nervous system myelin. Four human isoforms have been identified. The most abundant is a highly conserved 18.5 kDa polypeptide. For this species, the amino acid sequence homologies between human and monkey or human and chick are 98.2% and 71.1%, respectively. As a consequence, there is a very good immunological cross-reactivity between the mammalian MBP. This protein has been extensively used to induce experimental allergic encephalomyelits (EAE) in numerous animals. The evolution of chronic EAE in animal is similar to that of multiple sclerosis (MS), a demyelinating human pathology, and chronic EAE is considered to be an animal model of MS. In demyelinating pathologies, MBP concentration in the cerebrospinal fluid (CSF) is considered to be a good marker of demyelination. MBP concentration, in biological fluids, is generally determined by radioimmunoassay (RIA). The RIA technique currently used is highly sensitive (0.1-2.5 ng/ml) but has the drawback of requiring the handling of radioactivity and frequent labelling of MBP. So we developed a new enzyme immunoassay (EIA) technique. Our technique has the same sensitivity as RIA, needs only small volumes of CSF (50 microliters) and the enzyme-labelled MBP tracer is stable for at least 12 months.

Oral tolerance in EAE: reversal of tolerance by T helper cell cytokines

Oral administration of myelin basic protein (MBP) inhibits clinical and histopathological manifestations of experimental autoimmune encephalomyelitis (EAE), but only partially reduces serum anti-MBP antibody titers. We report here that orally administered MBP alters the isotypic distribution of anti-MBP antibody-forming cells (AFC) among various lymphoid tissues, with the most profound differences seen in mucosal tissues. We observed an isotype-selective reduction in anti-MBP IgA but not IgM AFC frequencies in Peyer's patches. The anti-MBP IgA AFC frequencies could be reconstituted by addition of interleukin 4 (IL-4) and interleukin 5(IL-5). The cytokines did not appear to generate de novo responses since no increases in anti-MBP lgA AFC frequencies were observed in control cultures. These results indicate that decreased antibody production, as a result of oral antigen administration, can be reversed by exposure to the appropriate cytokines.

Ciliary neurotrophic factor and leukemia inhibitory factor promote the generation, maturation and survival of oligodendrocytes in vitro

We have found that CNTF and LIF are pleiotropic modulators of development in the O-2A lineage. Both molecules enhanced the generation of oligodendrocytes in cultures of dividing O-2A progenitors. CNTF and LIF also promoted oligodendrocyte maturation, as determined by expression of myelin basic protein, and could promote oligodendrocyte survival to an extent comparable with insulin-like growth factor-1 or insulin. In addition, LIF and CNTF both promoted the differentiation of O-2A progenitors into type-2 astrocytes but only when applied in the presence of extracellular matrix (EnMx) derived from cultures of endothelial cells. The ability of CNTF and LIF to enhance differentiation of O-2A progenitors along either of the alternative pathways of oligodendrocyte and astrocyte differentiation suggests that these proteins are able to enhance the process of differentiation per se, while the actual path of differentiation promoted is determined by the presence or absence of additional molecules in the extracellular environment.

Cerebrospinal fluid markers in neurological disorders

Cerebrospinal fluid (CSF) markers are a useful tool for determining disease progression or activity in some neurological disorders which need parameters both for evaluating treatments and investigating pathobiological evolution in research-oriented follow-up. A number of CSF proteins are reviewed with data on biological properties, analytical methods, clinical usefulness of: myelin basic protein, S-100 protein, glial fibrillary acidic protein, neural-cell adhesion molecule, neuron-specific enolase and others.

Oral tolerance in experimental autoimmune encephalomyelitis: serum and salivary antibody responses

We have recently reported that the oral administration of myelin basic protein (MBP) prior to encephalitogenic challenge results in suppression of experimental autoimmune encephalomyelitis (EAE). We examined the serum and salivary antibody responses to MBP in orally tolerant rats using an avidin-biotin enzyme-linked immunosorbent assay. Serum anti-MBP IgA and IgG, but not IgM levels are suppressed in orally tolerant versus control rats. This suppression is time dependent and is confined to the period when animals would otherwise be manifesting EAE clinical signs. In contrast, there is an increase in salivary anti-MBP IgA levels in MBP-fed rats relative to vehicle-fed controls. Thus, MBP-induced unresponsiveness is demonstrable at the humoral level, and moreover, a discrete compartmentalization between the serum and salivary anti-MBP responses exists.

Herpes simplex virus infection and damage in the central nervous system: immune response to myelin basic protein

Two models of herpes simplex virus (HSV) infection in the mouse (inoculation of the ear pinna or intravenous inoculation) were used to assess immune responses to the virus and myelin basic protein (MBP). In both models demyelination in the central nervous system (CNS) can be assessed by clinical signs; ear paralysis (ear inoculation) and hind limb paralysis (intravenous inoculation). In the ear model, low levels of antibody to MBP were detected at 7 and 14 days after inoculation. The incidence of such antibody was low and bore no correlation with signs of paralysis. Cells from draining lymph nodes of mice inoculated in the pinna showed a proliferative response to HSV and MBP in vitro. In both models, delayed-type hypersensitivity reactions were demonstrated against HSV and MBP but such reactions were most significant after i.v. inoculation. This may reflect the greater CNS damage associated with hind limb paralysis.

Purification and characterization of glia maturation factor beta: a growth regulator for neurons and glia

A protein has been isolated from bovine brains by using a modification of the procedure used to purify glia maturation factor. The method consists of ammonium sulfate precipitation, chromatography with DEAE-Sephacel, Sephadex G-75, and hydroxylapatite columns, passage through a heparin-Sepharose column, and finally fractionation by reverse-phase HPLC with a C4 column. The isolated protein reacts strongly with the mouse monoclonal antibody G2-09 and has a molecular weight of approximately 17,000 and an isoelectric point of pH 4.9. The N terminus is blocked, but tryptic digestion releases 28 peptides, 8 of which have been sequenced. The total known residues add up to more than two-thirds of the entire 140-residue protein, estimated from amino acid composition, and show no sequence homology with any known protein. Reversible thermal renaturation greatly enhances its biological activity. The purified protein stimulates differentiation of normal neurons as well as glial cells. It inhibits the proliferation of the N-18 neuroblastoma line and the C6 glioma line while promoting their phenotypic expression. We designate this protein glia maturation factor beta.

Detection of antibodies against myelin basic protein and increased levels of HIV-IgG antibodies and HIV antigen after solubilization of immune complexes in sera and CSF of HIV infected patients

Fifteen HIV seropositive patients were studied. It was possible to enhance detection of HIV antigen and HIV and myelin basic protein (MBP) antibodies after dissociation of immune complexes by acid hydrolysis. HIV p24 antigen was then detected in four patients, three of whom were previously antigen negative. In 14 patients the treatment resulted in increased anti-HIV IgG subclass levels. Anti-MBP IgG was detected in 12 patients. Intrathecal synthesis of anti-MBP IgG subclasses was found in eight patients, five of whom had symptoms from the central nervous system.

Experimental allergic encephalomyelitis in mice: presence of myelin basic protein in cerebrospinal fluid

The concentration of myelin basic protein (MBP) in cerebrospinal fluid (CSF) correlates with the development of experimental allergic encephalomyelitis following intradermal injection with encephalitogen in adjuvant; MBP is absent in controls inoculated with adjuvants only. The presence of MBP is a sensitive indicator of disease inasmuch as CNS-inoculated mice with neurologic signs had an average of 0.29 ng/microliter of MBP in their CSF and controls, including normal or adjuvants only, had an average of 0.03 ng/microliter. The amount present per microliter of CSF, as well as the absolute amount, obtained from an individual mouse do not always reflect the severity of disease as indicated by clinical signs and the pathology observed in a sampling of the neuraxis. The presence of MBP does correlate with demyelination, although the extent of pathology observed by light microscopy in the mouse model is minimal, associated only with the inflammatory response, and does not extend beyond the zone of the perivascular cuff.

Chronic Theiler's virus infection in mice: appearance of myelin basic protein in the cerebrospinal fluid and serum antibody directed against MBP

Myelin basic protein (MBP) appears frequently in the cerebrospinal fluid (CSF) of mice with chronic demyelination following intracerebral infection with Theiler's murine encephalomyelitis virus (TMEV); antibody to MBP can frequently be found in the sera. The peaks of the immune responses to both MBP and TMEV coincide with the time course of the clinical signs of disease. Adsorption of mouse sera with TMEV or MBP indicate the non-identity of the antigens and the specificity of the antisera as measured by ELISA. Immunoblot analysis of sera confirmed the ELISA findings. The mechanism of induction of antibody directed against MBP and its role in TMEV-associated demyelination remain to be determined.

Serum and cerebrospinal fluid antibodies against myelin basic protein and their IgG subclass distribution in multiple sclerosis

IgG class antibodies reactive with myelin basic protein (MBP) were determined by enzyme-linked immunosorbent assay (ELISA) in serum and cerebrospinal fluid (CSF) of 37 patients with multiple sclerosis and a control group of 32 patients with tension headache or psychoneurosis. Using standardised amounts of IgG from CSF and serum in ELISA, significantly higher mean antibody levels were found in CSF as well as in serum from the patients with multiple sclerosis. Ten (27%) of the multiple sclerosis CSF samples and 15 (41%) of the multiple sclerosis sera revealed anti MBP antibody levels exceeding 2 SD of the control group. Seven patients (19%) showed exclusive or higher levels of anti MBP antibodies in CSF, suggesting synthesis within the central nervous system. Analysis by ELISA for IgG subclasses of anti MBP antibodies revealed that they were restricted to IgG 1 in four patients and IgG 3 in one.

Evolutionary divergence in the structure of myelin basic protein: comparison of chondrichthye basic proteins with those from higher vertebrates

A basic protein has been purified from the CNS myelin of the gummy shark (Mustelus antarticus). Electroblotting was used to examine the capacity of rabbit antisera raised against this electrophoretically pure protein to recognize myelin basic protein from higher vertebrates. The antisera bound to two shark proteins including the original polypeptide antigen and to chicken, bovine, and human myelin basic proteins. Thus, the shark protein appeared to possess antigenic determinants that have been retained through evolutionary divergence of these proteins. Whereas bovine basic protein caused experimental allergic encephalomyelitis in guinea pigs, animals that received injections of the shark protein showed neither clinical nor histological signs of this disease. However, tests for delayed-type hypersensitivity and for Arthus reaction following injection with the shark protein revealed a T-cell-mediated response to this antigen and substantial cross-reactivity with higher vertebrate basic proteins. Analysis of the amino acid composition of the shark protein, and comparison of its tryptic peptide map with that of the bovine protein, revealed substantial changes in the amino acid sequence. Although the shark protein has some antigenic determinants in common with the proteins from higher vertebrates, it appears that much of the structure differs.

Rat and mouse monoclonal antibodies to human myelin basic protein

BALB/c mice and Lewis rats were immunized with human myelin basic protein and its N- and C-terminal fragments. Mouse X mouse fusions produced seven monoclonal antibodies, all of the IgG class and directed against the N-terminal fragment. Five of the antibodies seemed to be against the same epitope, between amino acid residues 92 and 118. One antibody bound between residues 45 and 91, and the remaining antibody reacted with both peptides 1-44 and 45-91. Three monoclonal antibodies, all of the IgM class, were obtained by rat X rat hybridization. Two monoclonal antibodies, raised against whole myelin basic protein and the C-terminal fragment, respectively, each bound to peptide 118-178. The remaining antibody, raised against the N-terminal fragment, bound to peptide 45-91. These monoclonal antibodies are of interest for use in clinical radioimmunoassays and for immunohistochemical investigation of the structural relationships of the myelin sheath.

Decreased levels of an astrocytic marker, glial fibrillary acidic protein, in the visual cortex of dark-reared rats: measurement by enzyme-linked immunosorbent assay

An antibody to glial fibrillary acidic protein (GFAP) (an immunocytochemical marker for astrocytes) has been used in an enzyme-linked immunosorbent assay (ELISA) to determine the amount of GFAP in three visual regions, the dorsal lateral geniculate nucleus (dLGN), the superior colliculus (SC) and the visual cortex (VC) (area 17) of dark-reared (D), normal (N) and light-exposed (L) rats. In all experiments GFAP was also measured in a control non-visual region, the motor cortex (MC) (area 4). No significant differences were found in GFAP in dLGN, SC or MC between D, L or N rats. However, in the visual cortex, the amount of GFAP in N rats was significantly greater than that in D rats (by 32%).

Myelin basic protein and demyelinating diseases

Myelin basic protein (MBP) is a major protein component of myelin sheath. Primarily because of its ability to induce experimental allergic encephalomyelitis (EAE) in animals, this protein has been considered to play an important role in the pathogenesis of multiple sclerosis (MS), which is one of the most common demyelinating diseases. Its precise measurement in the cerebrospinal fluid (CSF) has been uncommonly difficult, mainly due to immunoheterogeneity of MBP or MBP-like material. More recently, highly sensitive radioimmunoassay techniques utilizing well-characterized antisera have been developed that facilitated its use in the management of MS. The clinical course of MS is highly variable, and the disease is characterized by periods of remission and relapses. Many studies have demonstrated the release of MBP during relapses and elevated levels of MBP in the CSF can be detected if lumbar puncture is performed within 7 days of the onset of neurologic symptoms suggestive of MS. However, the presence of MBP is not an absolute indicator of MS, as elevated MBP levels are also frequently observed in other demyelinating diseases.

Characterization of antibodies against major fish CNS myelin proteins: immunoblot analysis and immunohistochemical localization of 36K and IP2 proteins in trout nerve tissue

Antisera against the trout CNS myelin proteins 36K and IP2 were prepared in rabbits and characterized by immunoblot analysis and immunohistochemistry. The anti-36K antiserum exclusively stained its corresponding antigen from trout CNS myelin but failed to recognize any myelin polypeptide from either trout PNS or mammalian CNS and PNS. Antibodies against the IP2 glycoprotein specifically cross-reacted with related intermediate proteins (IP) of both CNS and PNS myelin from trout but only faintly labeled the PO protein of mouse peripheral nerve. Immunohistochemical localization of both antigens in the CNS of young trout was confined to the myelin sheath, except that anti-36K antiserum also stained oligodendrocytes. Nodes of Ranvier, neuronal cell bodies, and dendrites, as well as other glial elements, were negative. Specificity of the immunofluorescent reaction was established by crossed immunoadsorption experiments. Whereas on adjacent sections through trout brain both antigens exhibited a nearly identical distribution pattern, immunostaining in peripheral nerves was seen only with anti-IP2 antibodies.

Measurement of myelin basic protein by radioimmunoassay in closed head trauma, multiple sclerosis and other neurological diseases

A double antibody sequential radioimmunoassay for human myelin basic protein (MBP) has been developed. The assay utilizes a rabbit antibody to human MBP and purified rabbit MBP as the radiolabelled antigen. This assay was used to analyze cerebrospinal fluid (CSF) from 22 patients with severe head injury, 61 other cases of various neurological disorders, and 106 normal controls. The results showed that closed head trauma caused moderate to severe elevations in CSF MBP, and elevated CSF MBP was detectable in several diseases which involve CNS myelin.

Immunoenzymoassay of the hyaluronic acid-hyaluronectin interaction: application to the detection of hyaluronic acid in serum of normal subjects and cancer patients

The binding of a hyaluronic acid-binding glycoprotein, hyaluronectin (HN), isolated from human brain, to hyaluronic acid (HA) was investigated with the enzyme-linked immunosorbent assay technique using plastic microtest plates coated with a 50 mg/liter solution of HA in 0.1 M bicarbonate. Optimum conditions for HN binding to HA were in 0.2 M NaCl buffered with 0.1 M sodium phosphate at pH 7. An assay for HA in solution was set up exploiting the fact that HN binding could be inhibited by soluble HA. HA was preincubated for 1 h in a test tube with a 30-ng/ml HN solution (v/v) in the buffer containing 0.1% bovine serum albumin. Incubation on HA-coated microtest plate lasted 4 h and maximum sensitivity was achieved when incubation was carried out at 4 degrees C. HN bound to the plate was revealed by means of alkaline phosphatase-conjugated anti-HN antibodies. The test was used to measure HA inhibitory activity after depolymerization by ferrous ions. No difference was found between inhibitory activity or smaller fragments and that of high-molecular-weight HA. The assay was applied to determination of HA in sera. Specificity was demonstrated by Streptomyces hyaluronidase digestion of reactive material in sera. Other glycosaminoglycans did not interfere with the assay. Recovery of HA was good and intra- and interassay variation coefficients were 6 +/- 2.2 and 12%. In 103 blood donor sera, HA was found at 22.4 +/- 16.7 micrograms/liter. HA was elevated in most of the cancer patient sera tested.

Comparison of the major proteins of shark myelin with the proteins of higher vertebrates

On gel electrophoresis in dodecyl sulphate solutions shark CNS myelin showed four bands close in mobility to the proteolipid protein of bovine CNS myelin. They had apparent molecular weights of 21,000, 26,000, 27,000, and 31,500. Unlike bovine proteolipid protein, all of these shark proteins were shown to be glycosylated by staining gels with the periodate-Schiff reagent. Amino acid analyses of the polypeptides eluted from polyacrylamide gels indicated a high content of apolar amino acids and a composition approximating that of the Po protein of bovine peripheral nervous system (PNS) myelin, rather than that of the CNS proteolipid protein. The shark polypeptide of apparent molecular weight 31,500 was obtained by elution from dodecyl sulphate gels and antibodies raised against it in rabbits. By probing of electroblots with this antiserum the four shark CNS bands were shown to share common determinants with each other, with a major shark PNS protein and with sheep and chicken major PNS glycoproteins (Po). The binding of antibody was unaffected by deglycosylation of the shark CNS polypeptides with anhydrous hydrogen fluoride. Together, these results appeared to establish that shark CNS myelin contains four proteins that are closely related to a major shark PNS protein and to the Po protein of higher species.

The cohydrolases in human spleen that stimulate glucosyl ceramide beta-glucosidase

A family of beta-glucosidase-stimulating proteins (called cohydrolase SPH-I here) was isolated from bovine, Gaucher human and control human spleens. All preparations exhibited a similar pattern of four major electrophoretic bands in polyacrylamide when stained with the cationic dye, Stains-All. The bovine bands migrated more rapidly, while the two types of human cohydrolase migrated very similarly. The two human preparations differed in several respects: the concentration was much higher in Gaucher spleen; the Gaucher factors eluted a little earlier from gel permeation and decyl agarose columns; much more of the cohydrolase was bound by a concanavalin A column; the control bands stained less intensely in gels than the Gaucher bands. Antibodies raised in rabbits to bovine cohydrolase reacted with all three preparations. All four bands from Gaucher cohydrolase showed similar ability to stimulate glucosidase and to bind the antibodies. It is evident that the cohydrolases from control and Gaucher spleens are similar in many respects, yet differ in some secondary fashion, possibly in carbohydrate content. It is suggested that Gaucher cohydrolase is formed from normal cohydrolase by the nonenzymatic action of cellular glucose over a period of many years, due to slowed catabolism of the cofactor.

An enzyme-linked immunosorbent assay for antibody against acetylcholine receptor

An enzyme-linked immunosorbent assay is described for measurement of antibody against Torpedo acetylcholine receptor. As here developed, the assay is highly sensitive, reproducible, and requires small quantities of immunological reagents. Relative measurements of antibody concentration by this method are proportional to those determined by radioimmunoassay.

Solid phase radioimmunoassay for human myelin basic protein using a monoclonal antibody

A solid phase competitive assay for human myelin basic protein (MBP) has been developed using a monoclonal antibody to MBP. The assay has been applied to the detection of antigenic peptides derived from MBP, the measurement of anti-idiotypic antibody and the detection of MBP in human serum.

Antigen-induced suppression of mitogen responses and resistance to experimental autoimmune encephalomyelitis

Random-bred Hartley and inbred Strain 2 and Strain 13 guinea pigs were inoculated for acute experimental autoimmune encephalomyelitis (EAE). Sixty-six percent (69/103) of the Hartleys developed signs of EAE while the remaining 34% (34/103) were resistant. No Strain 2 and all Strain 13 guinea pigs developed EAE. Histologic examination of nervous tissue revealed that susceptible Hartleys and Strain 13 and Strain 2 animals had lesions characteristic of EAE. Tissue from resistant Hartleys showed fewer and less severe changes. Lymphocyte-transformation assays with EAE-inducing and noninducing antigens and T-cell mitogens revealed three different sets of responses in vitro: (i) lymphocytes from all animals responded to mitogens; (ii) lymphocytes from susceptible animals responded to EAE-inducing antigens; and (iii) lymphocytes from resistant Hartleys were suppressed from responding to the mitogens solely by EAE-inducing antigens. Plasmas from all EAE-sensitized animals had equivalent anti-myelin basic proteins (MBP) antibody titers and skin tests of EAE-inoculated Hartleys were all positive for MBP sensitization. Therefore, resistance and reduced histologic changes characteristic of EAE correlated with a disease-specific antigen-induced suppression of lymphocyte responses to T-cell mitogens. This suggests that clinical resistance to EAE in Hartley guinea pigs is mediated by an immunologic suppressor mechanism.

Enzyme-linked immunosorbent assay for leucine and methionine enkephalins

An enzyme-linked immunosorbent assay for enkephalins was developed by coupling the peptides to a carrier molecule (bovine serum albumin) in order to allow the antibody-antigen reaction to take place in the solid phase. The assay was shown to be highly reproducible. Its sensitivity was 14 nmol/liter for leucine enkephalin and 27 nmol/liter for methionine enkephalin, which is similar to that obtained when the same antibodies were used in radioimmunoassay.

Development and applications of a solid-phase radioimmunoassay for the PO protein of peripheral myelin

This is the first report of a quantitative radioimmunoassay for PO. The assay uses antigen-coated plastic microwells, with antibody binding detected by 125I-labeled protein A. Either peripheral myelin proteins or purified PO may be used as the antigen. Optimal extraction of tissue samples for PO immunoassay requires careful attention to the sodium dodecyl sulfate-to-protein ratio. Sodium dodecyl sulfate interference with antibody binding can be minimized by adding an excess of nonionic detergent and carrier protein to the incubation buffer. This method allows the detection of 0.8 ng of PO (20 ng/ml). Results from this assay showed little or no immunoreactivity in extracts of brain, centra myelin, liver, purified myelin basic proteins, cultured, purified secondary Schwann cells, or membrane preparations from these cells. PO was clearly detectable in Schwann cell cultures from 3- to 4-day-old rats at 12-18 h after dissociation (4% of the level in adult sciatic nerve) and in extracts of one-day-old rat sciatic nerve (2% of the level in adult nerve). Myelin basic protein radioimmunoassays showed that the ratio of PO to myelin basic protein is essentially constant in extracts of sciatic nerve from ne-day-old, four-day-old, and young adult rats. Another result was that PO levels are reduced in the trembler mouse sciatic nerve.

Measurement of myelin basic protein and of anti-basic protein antibodies by ELISA utilizing biotinylated antibodies

Immunoglobulins were conjugated to peroxidase by the biotin-avidin method and used in ELISA systems for measuring myelin basic protein (MBP) and anti-MBP antibodies. To measure concentration of MBP, microplate wells were coated with affinity purified rabbit anti-MBP antibodies and incubated with varying concentrations of MBP. Bound antigen was measured by incubating with biotinylated anti-MBP antibodies and avidin-peroxidase. As little as 0.2 ng/ml of MBP could be measured by this assay. To measure anti-MBP antibodies, microplate wells were coated with human MBP and incubated with varying concentrations of affinity purified rabbit anti-human MBP antibodies. Binding was measured by incubating with either peroxidase-conjugated anti-rabbit antibodies or biotinylated anti-rabbit antibodies and avidin peroxidase. The two methods were equally sensitive. The avidin-biotin method for enzyme conjugation promises to be a useful and versatile tool for ELISA systems.

Radioimmunoassay of myelin basic protein. A methodological evaluation

Three techniques for separating free antigen from antigen-antibody complexes have been applied to radioimmunoassay of myelin basic protein: cold ethanol precipitation of complexes, dextran-coated charcoal precipitation of free antigen, and second antibody precipitation of complexes. After optimization of the incubation and separation steps, the 3 methods were evaluated for precision and accuracy when applied to both spinal fluid and brain tissue homogenates. For determinations in brain tissue all 3 methods showed the same precision and gave largely the same values, though the ethanol method gave slightly lower levels. For spinal fluid the ethanol and dextran-charcoal methods gave the same values, but the double antibody method gave values only 1/3 as high. With spinal fluid, the precision of the dextran-charcoal method was poor compared with that of the other two. The double antibody method proved to be the method of choice for brain tissue samples, when the results of the incubation and separation steps, and the precision and accuracy of the determinations were taken into account. However, for an unknown reason values for spinal fluid were too low by this method. Therefore the ethanol precipitation method is recommended for spinal fluid samples and the double antibody method for brain tissue samples.

Enzyme immunoassay of the myelin basic protein

An enzyme immunoassay using a double-antibody solid-phase technique for myelin basic protein (MBP) has been developed. Antisera were prepared by immunizing rabbits with the purified MBP from chick brain. The conjugation of MBP with horseradish peroxidase was performed by the periodate oxidation method in triethanolamine-acetate buffer (pH 8.5). The sample, antiserum, and conjugate were incubated at 4 degrees C for 16 h, after which the insoluble second antibody was added and the reaction mixture was incubated at 4 degrees C for 3 h. The peroxidase activity of the insoluble conjugate was assayed fluorometrically with hydrogen peroxide and 3-(p-hydroxyphenyl)propionic acid as substrates. The method had an analytical range from 50 pg to 1 ng (from 2.3 x 10(-15) to 4.5 x 10(-14) mol). The within-assay coefficient of variation (CV) was between 4 and 11% and the between-assay CV for 200 and 400 pg of MBP was 5.5 and 7.1%, respectively. A weak cross-reactivity was observed between chick MBP and bovine MBP, while no reactivity was shown with calf thymus histone. The MBP content of the brain during development increased markedly from the 3rd embryonic week to the 3rd post-hatch week (from 0.01 to 2.4 mg/g of fresh tissue), and the adult level was 3.2 mg/g of fresh tissue.

Further studies on bacterial lipopolysaccharide-induced protection against experimental allergic encephalomyelitis in guinea pigs. Effects of chemical modifications

Bacterial lipopolysaccharide (LPS)-induced protection against experimental allergic encephalomyelitis (EAE) was studied in guinea pigs using chemically modified derivatives. Hydroxylaminolysis or alkaline hydrolysis of LPS, by which ester-linked fatty acids are removed from LPS, resulted in total loss of its mitogenic activity for B lymphocytes, and EAE-suppressive activity was simultaneously reduced. Similar diminished activity was observed in delayed-type skin reactions to myelin basic protein (BP) and anti-BP antibody production detected by passive hemagglutination and enzyme-linked immunosorbent assay (ELISA). These results indicate that the active site of LPS in suppressing EAE is in the lipid portion and that there exists a good correlation between the capacity of LPS to suppress EAE and its mitogenic activity.

Antibodies to P2 and P1 myelin antigens in experimental allergic neuritis and allergic encephalomyelitis

We confirmed earlier observations that experimental allergic neuritis (EAN) in Lewis rats induced by injection of bovine peripheral nerve myelin in complete Freund's adjuvant is not accompanied by development of experimental allergic encephalomyelitis. However, sera of these animals contained elevated titers of antibodies against central nervous system myelin basic protein (BP), likely induced by peripheral nerve P1 protein. Anti-BP antibodies were not seen in sera of rats with EAN induced by peripheral nerve P2 protein. Lack of encephalogenicity of bovine myelin in Lewis rats does not reflect simply lack of immune responses induced against BP.

Enzyme-linked immunosorbent assay of substance P: a study in the eye

A solid phase enzyme-linked immunosorbent assay for quantitation of substance P is presented. The assay measures the capacity of soluble substance P to compete with the solid phase antigen for a limited quantity of specific substance P antibody. The solid-phase antigen consists of a synthetic substance P.poly-D-glutamic acid conjugate coated to polystyrene micro-ELISA plate wells. Soluble substance P and antibodies to substance P are first preincubated together and then added to the wells containing solid-phase antigen. Subsequently the wells are incubated with anti-antibodies conjugated to alkaline phosphatase. The wells are finally incubated with p-nitrophenyl phosphate an the absorbance is read in a spectrophotometer 16--24 hr after the start of the assay. The threshold for detection of substance P was 5--10 pg per well (0.25 ml). Substance P was extracted from rabbit eyes and the values obtained with the present method are compared with previously reported values based on radioimmunoassay.

Solid-phase immunoassays for quantitation of antibody to bovine white matter proteolipid apoprotein

Two solid-phase immunoassays have been developed for quantitation of antibodies to bovine white matter proteolipid apoprotein. Conditions were established for optimal specific antibody binding. Water-soluble proteolipid apoprotein was bound to microtiter plates and plates were incubated with test serum. Goat anti-rabbit IgG conjugated with horseradish peroxidase was used as the second antibody for an enzyme-linked immunospecific assay and 125I-labeled protein A for a radioimmunoassay. Both procedures have been used to follow the time course of anti-proteolipid antibody production in rabbits and to compare different immunization protocols.

Fucose incorporation and identification of fucosylglycoproteins in synaptosomes

A synaptosome-enriched fraction from sheep cortex was incubated with L-fucose. The uptake of the sugar into this preparation was dependent on time, temperature, and concentration. A Kmapp of 0.94 mM-L-fucose and a Vmaxapp value of 0.24 nM-L-fucose/mg synaptosomal soluble protein/20 min was determined. After incubation for 10 min at 25 degrees C with L-[3H]fucose, 70% of the radioactive label was found in the soluble fraction. DEAE-cellulose chromatography resulted in the elution of three fucosylprotein peaks which were then characterised by gel filtration and sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE). At least eleven 3H protein-staining bands were identified with M. W. 13,000--115,000. Control experiments involving the incubation of the hexose with heat-treated synaptosomes and myelin, mitochondria, and microsomes indicted that the tritiated material associated with the synaptosomal soluble fraction was not due to nonspecific binding or to the presence of contaminating subcellular material. A 3H glycopeptide was identified, and on analysis the carbohydrate moiety was found to be rich in sialic acid, fucose, galactose, mannose, and N-acetylglucosamine. Mild acid treatment of the glycopeptide released fucose, which implies that this carbohydrate occupies a terminal position in the oligosaccharide chain. From these results it is proposed that synthesis or the modification of soluble fucosylglycoproteins is possible in synaptosomes.

Plasma myelin basic protein assay using Gilford enzyme immunoassay cuvettes

The assay of myelin basic protein in body fluids has potential clinical importance as a routine indicator of demyelination. Preliminary details of a competitive enzyme immunoassay for this protein have previously been published by the author (Groome, N. P. (1980) J. Neurochem. 35, 1409-1417). The present paper now describes the adaptation of this assay for use on human plasma and various aspects of routine data processing. A commercially available cuvette system was found to have advantages over microtitre plates but required a permuted arrangement of sample replicates for consistent results. For dose interpolation, the standard curve could be fitted to a three parameter non-linear equation by regression analysis or linearised by the logit/log transformation.