Immunogenicity of synthetic peptide sequences S81 and S82 (residues 68-83 and 65-83) of bovine myelin basic protein. Time-course of antibody responses in rats and rabbits

A review of stress-relapse interactions in multiple sclerosis: important features and stress-mediating and -moderating variables

Studies do not provide a consensus opinion of the relationship between stress and relapse in relapsing=remitting multiple sclerosis (RRMS). Few studies have defined the critical features of these stressful situations, or examined the role of stress-mediating and -moderating variables. Available evidence indicates that the relationship between life stress and relapse is complex, and is likely to depend on factors such as stressor chronicity, frequency, severity and type, and individual patient characteristics such as depression, health locus of control and coping strategy use. Little is known about how these factors, individually or in combination, are related to MS disease activity. Viral infections are also likely to precipitate relapse in MS, and significant life-stress may further enhance this relationship. The nature and strength of these interrelationships have strong clinical implications. MS patients are particularly vulnerable to a deteriorating cycle of stressful life events, illness episodes and disability. Timely multidisciplinary care interventions aimed at both minimizing psychological distress and physical symptoms may halt this downward reciprocal cycle. Little is known of the pathogenesis of these putative stress-induced changes in disease activity, and almost all stressor studies suffer from some biases or limitations.

Peptide bond specificity of calpain: proteolysis of human myelin basic protein

In order to determine the peptide bond specificity of calpain, human myelin basic protein (HMBP) was treated with purified calpain of bovine brain. Upon incubation, HMBP component I (HMBP-I) was degraded into several peptides as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Component I was more susceptible to degradation than components II and III. HMBP degradation products were separated by high performance liquid chromatography (HPLC) and the cleavage sites in HMBP molecules were determined by peptide sequence analysis and by N- and C-terminal analyses. The major cleavage site was found to be 94Val-95Thr with several minor cleavages at 49Arg-50Gly, 18Ala-19Ser, 23His-24Ala, 27Gly-28Phe, 59Asp-60Ser, 70Gly-71Ser, 97Arg-98Thr, 110Ser-111Leu, 145Asp-146Ala, and 156Leu-157Gly. These results indicate that calpain is involved in the limited proteolysis of human myelin basic protein and prolonged incubation causes further digestion of the large peptides.

A correlation between cerebrospinal fluid myelin basic protein and anti-myelin basic protein in multiple sclerosis patients

Free and bound levels of myelin basic protein (MBP) and anti-myelin basic protein (anti-MBP) antibodies were measured by radioimmunoassay in the cerebrospinal fluid of patients with multiple sclerosis who were experiencing acute exacerbations or progressing disease. In a cross-sectional study, free levels of MBP correlated with those of free anti-MBP, and bound MBP levels correlated with those of bound anti-MBP in both groups of patients with active disease. However, acute exacerbations of multiple sclerosis were characterized by higher free MBP and anti-MBP levels with lower levels of bound fractions. Conversely, patients with progressing disease had higher titers of bound than free fractions. Longitudinal studies of individual patients confirmed the association of higher titers of free anti-MBP with acute exacerbations and higher levels of bound anti-MBP with chronic progressing disease.

Synthetic peptide analogs to probe the immunological expression of the rat encephalitogenic neuropeptide

The rationale for designing and synthesizing 24 different peptide analogs and subpeptides of residues 69-84 of guinea pig myelin basic protein is presented. The encephalitogenic potential of 19 of these peptides in Lewis rats is also given.

Experimental allergic encephalomyelitis (EAE): role of B cell and T cell epitopes in the development of EAE in Lewis rats

Studies from our laboratory have shown that classical clinical and histological signs of experimental allergic encephalomyelitis (EAE) may be induced in Lewis rats by synthetic peptides S49 or S55. Peptides S49S and S55S are defined by residues 69-84 and 72-84 of the guinea pig myelin basic protein (MBP), respectively. Peptide S53 (residues 75-84 of the guinea pig MBP), six residues shorter than S49S at the N-terminal end, induced mild clinical signs of disease unaccompanied by hind leg paralysis, incontinence, or central nervous system pathology. In contrast, peptide S67 (residues 69-81 of the guinea pig MBP), three residues shorter than S49S at the C-terminal end, did not induce either clinical or histological signs of EAE despite the fact that the S67-sequence houses an epitope known to induce cell-mediated immunity. Peptides S49S, S55S, and S53 are antigenic and gave rise to antibodies that recognized either of the three peptide sequences. In this report we explore the interrelationship between cellular immunity induced by the S67 sequence and humoral immunity, induced by the S53 sequence and the development of classical clinical and histological signs of EAE. The results show that the nonencephalitogenic sequence of S67 may be rendered encephalitogenic in the presence of antibody directed against the S53 sequence. Lewis rats immunized with S53 developed pathological signs of EAE only after they were challenged with S67. The fact that a simultaneous challenge with S67 and S53 was as effective in inducing EAE pathology as a delayed one (up to 40 days) suggests that the cellular response to S67 is dependent upon the humoral response to S53.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyclonal antibodies to the encephalitogenic neighborhoods of myelin basic protein: singular affinity populations neutralized by specific synthetic peptide probes

Specific ligand neutralization was used to probe the extent to which singular antibody affinity populations signified specific determinants in the neighborhood myelin basic protein (MBP) encephalitogens. The probes were individual members of a panel of synthetic peptide analogs subsuming encephalitogenic regions. Comparative Scatchard analyses of neutralized and unneutralized antisera helped to identify the particular peptide determinants involved in the original polyclonal antibody responses to the multiple antigenic determinants of encephalitogenic peptides. The range of affinities for an antibody population against a singular MBP peptide determinant was found to be relatively restricted while the range of affinities overall for all populations within a given antipeptide antiserum was found to be relatively wide and invariably discontinuous. Consequently, the individual discontinuous affinity populations could readily be dissected by application of the Rosenthal method of Scatchard curve analysis. It was found that the singular high affinity antibody population (5.6 x 10(7) M-1) of a Lewis rat antiserum to rat encephalitogenic GSLPQKAQRPQDENG (S49) was against a determinant near the N-terminal non-encephalitogenic end of the peptide. Only the low affinity antibody populations were found that had reactivity for determinants within the encephalitogenic region itself. The singular high affinity antibody population (5.97 x 10(7) M-1) of a rabbit antiserum to rabbit encephalitogenic TTHYGSLPQKAQGHRPQDEG (S82) was against a determinant centered about the tyrosyl residue, within the encephalitogenic region for the rabbit, but was completely cross-reactive with a specific circulating endogenous inhibitor. The results obtained with the rat and rabbit EAE sera were consistent with a previously advanced hypothesis that antibodies to determinants within encephalitogenic neighborhoods would effectively block the onset of EAE if high enough in affinity and not neutralized by an endogenous inhibitor.

Monoclonal and polyclonal antibodies to myelin basic protein determinants

A detailed immunochemical examination of monoclonal and polyclonal antibody responses to myelin basic protein (MBP) and its peptides has revealed the existence of as many as 27 antigenic determinants, many of them conformational. Topological mapping of the potential antigenic determinants onto a model of MBP secondary structure places these determinants within 11 separate regions of the molecule, including those portions that have been found to be encephalitogenic. MBP and its peptides, therefore, fall under the umbrella of the Multideterminant-Regulatory Model of Benjamin et al. (1984). However, in the case of MBP, multideterminant immunogenicity appears to represent mainly an escape from tight regulation through the avenue of conformational change.

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.

Biological activity of region 65-102 of the myelin basic protein

Region 65-102 of the myelin basic protein (MBP) houses a number of antigenic determinants known to induce delayed-type hypersensitivity, experimental allergic encephalomyelitis (EAE), suppressor cell function, and antibodies. In this report we describe the biological activity of synthetic peptides S53, S55, and S49 with sequence homology to region 69-84 of the rat, guinea pig, and bovine MBP. Peptide S53-A, defined by residues 75-84 of the guinea pig (SQRSQDEN) and of the rat (SQRTQDEN) MBP induced clinical signs of disease in Lewis rats. These included weight loss, flaccid tail, "muscle wasting," and hind-leg weakness. Histological examination of brain, spinal cord, and sciatic nerve sections of diseased rats revealed the complete absence of focal and perivascular lymphocytic infiltrates characteristics of demyelinating EAE lesions. Elongation of peptide S53 by three or six residues to residue sequences naturally found at its N-terminal end gave rise to peptides S55S (PQKSQRSQDEN) and S49S (GSLPQKSQRSDQDEN), respectively. Lewis rats challenged with either S55S or S49S developed classical clinical and histological signs of EAE. Severe hind-leg paralysis was accompanied by incontinence and sometimes death. Injected in the form of carrier-free peptide, S53 was a meager B cell immunogen. S53 conjugated with methylated-bovine serum albumin was also a potent immunogen and produced clinical signs of disease without CNS pathology. By comparison, carrier-free S55S and S49S were potent immunogens giving rise to antibodies that cross reacted completely and competitively with S55S but considerably less so with S53. The results show that the sequence of S53 defines an epitope responsible for the formation of anti-S53 antibodies. Elongation of the S53 sequence at its N-terminal end generated an additional epitope which induced cell-mediated immunity responsible for the concomitant development of pathological signs of EAE. It may be concluded that the induction of classical signs of EAE requires specific and defined sequences capable of expressing both B cell and T cell functions.

Affinity purification of two populations of antibodies against format determinants of synthetic myelin basic protein peptide S82 from S82-AH- and S82-CH-Sepharose 4B columns

Two different kinds of immunosorbents were prepared that contained the synthetic myelin basic protein didecapeptide S82 (TTHYGSLPQKAQGHRDQDEG)--one coupled with AH-Sepharose 4B through hexanoate spacers to the C-terminal glycyl residue; the other, with CH-Sepharose 4B through hexanoate spacers to the N-terminal threonine residue. An antiserum rich in antibodies to a format determinant of S82 was passed through each column, and, by means of affinity purification, two homogeneous populations of anti-format antibodies were obtained, each with a binding affinity of 1 X 10(8)M-1 for S82. The population recovered from S82-AH-Sepharose 4B cross-reacted to a considerable extent with synthetic peptide S8 (GSLPQKAQGHRPQDENG) but only to a limited extent with S79 (AQGHRPQDEG). The population recovered from S82-CH-Sepharose 4B cross-reacted poorly, if at all, with S8. An equimoler mixture of S8 + S79, however, reacted well with either population of anti-format antibodies, thus showing that the mixture could mimic the format of S82. It was concluded that secondary structural conformation of S82 could be preserved during the coupling procedure and that the resulting immunosorbents could be used for the affinity purification of anti-S82 antibodies to the format determinants.

Format determinants of synthetic myelin basic protein peptide S82 mimicked by a mixture of synthetic peptides S8 and S79

Antibodies to synthetic myelin basic protein peptide S82 (TTHYG-SLPQKAQGHRPQDEG) did not react with synthetic peptide S8 (GSLPQKAQGHRPQDENG) and only partially so with synthetic peptide S79 (AQGHRPQDEG); however, the antibodies did react to a considerable extent with an equimolar mixture of S8 and S79. Since the anti-S82 antibodies had previously been shown to be directed to a non-sequential format determinant dependent on the conformation of secondary structure, it seems probable that the mixture of S8 and S79 assumed a format that neither one individually possessed to any great degree.

Immunochemical cross-reactivity between intact purified myelin basic protein (MBP) and the synthetic encephalitogenic peptide S49

Three antisera to myelin basic protein--a rabbit antiserum pool against rat myelin, a rabbit antiserum pool against rat myelin basic protein (MBP), and a monkey antiserum against bovine MBP--were found to contain detectable levels of antibodies that would bind radiolabeled S49 (GSLPQKAQRPQDENG). Strongly encephalitogenic in Lewis rat, S49 is a synthetic peptide representing residues 69-84 of bovine MBP with a deletion of glycine-76 and histidine-77 to make it analogous to rat and guinea pig MBPs. The rabbit antimyelin antiserum and the monkey anti-MBP antiserum contained antibodies directed against a non-sequential determinant that required asparagine 84, the glycine-histidine deletion, and residues 69-71 for maximal activity. S49-reactive antibodies from the rabbit anti-MBP antiserum were directed solely against a sequential determinant comprising residues 69-71, S49-reactive antibodies from all three antisera reacted in liquid phase with purified intact rat, guinea pig, and bovine MBP showing that the determinant is exposed for B cell recognition even in bovine MBP and can serve both as immunogen and reactant.

The appearance of a new antigenic determinant during the degradation of myelin basic protein

Studies were undertaken to determine of a previously unrecognized or inaccessible antigenic determinant might be exposed during the course of digestion of basic protein by a normal brain enzyme. As studied by double antibody radioimmunoassay, exposure of bovine brain myelin basic protein to bovine brain cathepsin D led to the appearance of an antigenic determinant recognized by an antibody reactive predominantly with the molecular region of BP encompassing residues 79-88. The 5 major microheterogeneous components of basic protein demonstrated this phenomenon. These results indicate that a normally appearing enzyme in brain known to the present in a number of cell types including oligodendrocytes can lead to the appearance of peptides of basic protein whose antigenic determinants may not be revealed in the intact molecule. This finding suggests that a number of basic protein peptides may be released by a similar mechanism so that efforts made to detect and quantitate such peptides must be capable of recognizing their unique antigenic features.

Affinity purification of an acylated and radiolabelled synthetic derivative of residues 75-83 of bovine myelin basic protein, [125I]S79. A model for the purification of picomole quantities of specific peptide fragments of myelin basic protein and antibodies against them

Among the antibodies contained in a rabbit antiserum to synthetic peptide sequence TTHYGSLPQKAQGHRPQDEG (S82) of bovine myelin basic protein (residues 65-83 plus glycine), was a population reactive with a C-terminal determinant of S82 and cross-reactive with S79 (AQGHRPQDEG) but not S6 (AQGHRPQDENG). This antibody population was purified 153-fold by affinity chromatography from a minicolumn containing S79 coupled to CH-Sepharose 4B(TM) and eluted with 3 M MgCl2. The purified antibodies were then coupled to CNBr-activated Sepharose 4B(TM) and used to purify 125I-labelled, acylated S79 ([125I]S79), 3 M MgCl2 once again having been used to elute the labelled ligand. Sips distribution studies revealed appreciable heterogeneity of binding affinities of unpurified antibodies in their reaction with affinity-purified [125I]S79 or of purified antibodies in their reaction with unpurified [125I]S79 (heterogeneity constant a = 0.34 and 0.36, respectively). In contrast Sips distribution data indicated considerable restriction of binding of the purified antibodies in their reaction with purified labelled ligand (a = 0.92) with an average affinity constant of K0 = 1.56 X 10(8) M-1. The results indicate that the heterogeneous spectrum of binding affinities originally displayed by the unpurified S79-reactive antibodies in their reaction with unpurified labelled S79 was due both to the presence of some antibodies characterized by high affinity binding (K0 greater than 10(9) M-1) and of some labelled ligand with low binding affinity. The affinity chromatographic method as here described should prove advantageous in purifying and eventually characterizing picomolar amounts of serum factors, previously postulated to be fragments of myelin basic protein, that are reactive with reagent antibodies up to an affinity level of 10(8) M-1.

Equilibrium competitive inhibition analysis of synthetic peptide antigens from myelin basic protein as affected by the dual-dilution phenomenon

It was shown that 125I-labelled and unlabelled forms of synthetic encephalitogenic peptide S82 (residues 65-83 plus glycine) of bovine myelin basic protein (MBP-Bov) were equally competitive in dual-dilution radioimmunoassays with rat- and rabbit-anti-S82 antisera without causing much deviation even at the extremes of the dual-dilution binding curves (solved in terms of total S82). With other antisera the deviations caused by the addition of unlabelled S82 were much greater than would be expected among repetitive assays with labelled antigen alone, and the excessive deviations were usually more prominent in one region of the dual-dilution binding curve than in another. Thus, establishing equivalence between labelled and unlabelled antigen with respect to one antiserum even at several dilutions does not establish proportionate sharing with respect to all antisera at all antigen concentrations. A method of dual-dilution equilibrium competitive inhibition analysis was devised that took this precaution into account. By means of the method, synthetic MBP-Bov peptides representing different parts of the S82 sequence were compared with homologous S82 peptide for their inhibitory effects upon dually diluted [125I]S82-anti-S82 systems. By this process several different S82 determinants were pinpointed, some with high affinity antibodies, others with low affinity antibodies, yet others equally well at high or low affinity.

Equilibrium and nonequilibrium competitive inhibitions of antipeptide antibody binding by parent myelin basic protein and 18 related peptide sequences

Equilibrium and nonequilibrium competitive inhibition analyses of a number of antisera to peptide S81 and S82 sequences were carried out through the use of inhibition radioimmunoassays with [125I]S81, [125I]S82, and [125I]S79 and a panel containing 18 related peptides and five myelin basic protein preparations. Two principal determinants were identified, one of them sequential, the other nonsequential. The sequential determinant involved a peptide at or near the C-terminal end of S82 that could be blocked by an interchange of asparagine for glycine at the C terminus. The nonsequential determinant was dominant for a number of rabbit and rat antisera, both anti-S82 and anti-S81, and was shared not only by S81 and S82 but also by S8 and S80, i.e., the family of residues of bovine MBP sequence 69-83. Neither determinant was expressed in any of the myelin basic protein preparations, and the nonsequential determinant was not expressed in peptide sequences smaller than S8.