Suppressor cell regulation of encephalitogenic T cell lines: generation of suppressor macrophages with cyclosporin A and myelin basic protein.

Chronic relapsing experimental allergic encephalomyelitis (CR-EAE) can be adoptively transferred using myelin basic protein (BP)-specific helper T cell lines, and suppressor cells may be important in recovery from EAE. In order to generate suppressor cells, spleen cells obtained from BP-complete Freund's adjuvant (CFA) inoculated SJL/J mice and from normal mice were cultured for 7 days with medium, with cyclosporin A (CsA), or with CsA and antigen (BP or purified protein derivative of mycobacterium (PPD)). Cultured spleen cells were assayed for suppressor activity in vitro by coculture with BP-specific and PPD-specific helper T cell lines derived from SJL/J mice. Immunized donor spleen cells cultured with cyclosporin A (CsA) and BP were potent inhibitors of T cell line proliferation, and suppressor activity was increased 17-fold compared with control splenocytes. The number of suppressor cells required to suppress PPD-specific line proliferation by 50% (I50) was significantly higher than the number required to suppress BP-specific line proliferation, suggesting an antigen-specific component to the suppression. The major effector cell required for suppression was a large granular Mac-1+ cell with the functional characteristics of a macrophage. Suppressor activity persisted after depletion of Thy 1.2+ cells, but suppression was no longer antigen-specific, suggesting that culture of spleen cells with CsA and BP may generate suppressor macrophages which are antigen-nonspecific and Thy 1.2+ suppressor cells which are antigen-specific. These suppressor cells may be important in the regulation of CR-EAE and the techniques described for their generation may prove useful for treatment and prevention of disease.     

Antigenic determinants of bovine myelin encephalitogenic protein recognized by rabbit antibody to myelin encephalitogenic protein.

The antigenic determinants of bovine myelin encephalitogenic protein were investigated by quantitative complement fixation and hapten inhibition using rabbit anti-monkey protein and anti-bovine protein and purified and characterized fragments of bovine protein. The two regions of bovine encephalitogenic protein containing determinants were sequences 1 to 43 and 90 to 170. One rabbit antiserum recognized a determinant(s) probably in residues 15 to 40 while for another rabbit antiserum the determinant of 1 to 43 resided in 1 to 20. The determinant(s) of residues 90 to 170 involved the region around the tryptophan at position 116. Fragment 44-89, which contains the major encephalitogenic determinant for the rabbit, was virtually devoid of any reactivity with the rabbit anti-encephalitogenic protein. It appears that portions of the protein other than the encephalitogenic site are responsible for stimulation of bone marrow-derived cells and antibody production. In demonstrating selected regions of the protein as sites for antigenic determinants, the present immunochemical studies also suggest that the protein might have a more folded conformational alignment than previously suspected.     

Determinants of human myelin basic protein that induce encephalitogenic T cells in Lewis rats

Due to critical amino acid changes in the 72-89 sequence, the determinant of human (Hu) basic protein (BP) that induces experimental autoimmune encephalomyelitis (EAE) in Lewis rats most likely differs from rat and guinea pig BP. To discern encephalitogenic sequence(s), the immunodominant epitopes recognized by Hu-BP-specific T cell lines were identified using synthetic peptides that corresponded to the Hu-BP sequence. The Hu-BP-reactive T cell line contained two distinct specificities, one directed at the 87-99 (Hu) sequence restricted by I-E, and the second directed at the 55-74 (Hu) sequence restricted by I-A. T cells specific for the 87-99 determinant recognized both Hu- and Rt-BP, were highly encephalitogenic, and accounted for the experimental autoimmune encephalomyelitis-inducing activity of the Hu-BP line. T cells directed at the S55-74 (Hu) sequence did not recognize Rt-BP and were not encephalitogenic. The same TCR V genes (homologous to the mouse V alpha 2 and V beta 8 families) that we showed previously were utilized preferentially in response to the I-A restricted 72-89 encephalitogenic sequence were also present in T cell lines specific for both the S55-74 and S87-99 epitopes. These data indicate that encephalitogenic activity of BP in Lewis rats is related to discrete T cell epitopes that are present on or cross-react with rat-BP. Furthermore it would appear that genes in the TCR V alpha 2 and V beta 8 families are widely used in response to different BP epitopes restricted by either I-A or I-E molecules.     

The immune response of Lewis rats to peptide 68-88 of guinea pig myelin basic protein. I. T cell determinants.

A series of peptides, produced from peptide 68-88 by selective enzyme cleavage, were used to define the amino acid sequences required for the induction of experimental allergic encephalomyelitis (EAE), an in vitro lymphocyte proliferative response (LPR), and serum antibody by peptide 68-88 in the Lewis rat. Here we present data that indicate that the T cell determinants for induction of EAE, an LPR, and helper function in the production of antibody are located in the same region of the molecule and that a minimum of 13 amino acids are involved; i.e., residues 71-85.     

T cell specificity for class II (I-A) and the encephalitogenic N-terminal epitope of the autoantigen myelin basic protein

The role of class II restriction in T cell recognition of an epitope of the autoantigen myelin basic protein (MBP) has been investigated. Encephalitogenic PL/J(H-2u) and (PL/J X SJL/J(H-2s))F1 ((PLSJ)F1) clones, isolated after immunization with intact MBP, recognize the N-terminal 11 amino acid residues of MBP in association with I-Au class II molecules. The synthetic peptide MBP 1-11 has been tested in vivo for induction of EAE. Clinical and histological EAE occurs in PL/J and (PLSJ)F1 mice but not SJL/J. The class II restriction of T cells primed with MBP 1-11 has been examined in primary cultures in vitro. Similar to encephalitogenic T cell clones, isolated after continuous selection in vitro, the population of MBP 1-11-specific proliferative PL/J and (PLSJ)F1 T cells, recognize this epitope in association with I-Au class II molecules. Not all MBP-specific T cell clones which are restricted to I-Au class II molecules cause autoimmune encephalomyelitis. The specificity of these non-encephalitogenic clones has been examined in this report. These clones also recognize MBP 1-11. Thus recognition of an encephalitogenic T cell epitope is not sufficient for induction of EAE.     

Amino acid sequence of the encephalitogenic basic protein from human myelin

Myelin from the central nervous system contains an unusual basic protein, which can induce experimental autoimmune encephalomyelitis. The basic protein from human brain was digested with trypsin and other enzymes and the sequence of the 170 amino acids was determined. The localization of the encephalitogenic determinants was described. Possible roles for the protein in the structure and function of myelin are discussed.     

ADP-ribosylation of myelin basic protein by cholera toxin.

Cholera toxin ADP-ribosylates four types of myelin basic proteins (MBPs) of Mr 14,000, 17,500, 19,000 and 22,000 in rat brain myelin. On an analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, MBP underwent mono- and multi-(ADP-ribosyl)ation by cholera toxin and thus modified MBP migrated on the gel as several discrete protein bands, the molecular masses of which were apparently larger by 500-2000 daltons than that of the corresponding untreated MBP. On average, 1.1 mol of ADP-ribosyl residue was incorporated into 1 mol of MBP. Four types of purified MBPs were also ADP-ribosylated by cholera toxin dependent on GTP and the protein factor for the ADP-ribosylation. The results show evidence that MBP is one of major and specific substrates of cholera toxin in brain membranes.     

Characterization of the immune response to a secondary encephalitogenic epitope of basic protein in Lewis rats. I. T cell receptor peptide regulation of T cell clones expressing cross-reactive V beta genes.

In Lewis rats, immunization with myelin basic protein induces two distinct encephalitogenic T cell populations, those responding to the immunodominant 72-89 epitope and those specific for a secondary epitope including residues 87-99. The 72-89 specific T cells were I-A restricted and preferentially expressed V beta 8.2 in their TCR. To determine the fine specificity, MHC restriction, and TCR V beta gene use in T cells reactive to the secondary epitope, we characterized 23 T cell clones from the lymph nodes (LN) and spinal cords (SC) of rats immunized with either whole basic protein or synthetic peptides S85-99 and S87-99 that were found to be functionally similar. The S85-99/S87-99 specific clones from LN and SC were all encephalitogenic despite differences in recognition of intact basic protein and class II MHC restriction. Unlike LN clones that overexpressed V beta 8 (46%+) and V beta 6 (31%+), however, SC clones were strongly biased (86%+) in their expression of V beta 6. This V gene bias raised the possibility of TCR peptide therapy using V beta 6 peptides. The V beta 6 sequence was similar to V beta 8.2 in the CDR2 region, and the corresponding peptides from this region were found to be cross-reactive in vivo. Moreover, both peptides were effective in the treatment of EAE induced with either S85-99, biased in V beta 6+ and V beta 8+ T cells, or guinea pig basic protein, biased only in V beta 8+ T cells. These data demonstrate the presence of common immunogenic epitopes among subsets of TCR V region gene families that possess important regulatory activity on effector T cell function.     

Butyrophilin, a milk protein, modulates the encephalitogenic T cell response to myelin oligodendrocyte glycoprotein in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) induced by sensitization with myelin oligodendrocyte glycoprotein (MOG) is a T cell-dependent autoimmune disease that reproduces the inflammatory demyelinating pathology of multiple sclerosis. We report that an encephalitogenic T cell response to MOG can be either induced or alternatively suppressed as a consequence of immunological cross-reactivity, or "molecular mimicry" with the extracellular IgV-like domain of the milk protein butyrophilin (BTN). In the Dark Agouti rat, active immunization with native BTN triggers an inflammatory response in the CNS characterized by the formation of scattered meningeal and perivascular infiltrates of T cells and macrophages. We demonstrate that this pathology is mediated by a MHC class II-restricted T cell response that cross-reacts with the MOG peptide sequence 76-87, I GEG KVA LRIQ N (identities underlined). Conversely, molecular mimicry with BTN can be exploited to suppress disease activity in MOG-induced EAE. We demonstrate that not only is EAE mediated by the adoptive transfer of MOG74-90 T cell lines markedly ameliorated by i.v. treatment with the homologous BTN peptide, BTN74-90, but that this protective effect is also seen in actively induced disease following transmucosal (intranasal) administration of the peptide. These results identify a mechanism by which the consumption of milk products may modulate the pathogenic autoimmune response to MOG.     

Application of high performance liquid chromatography to the preparation of encephalitogenic myelin basic protein

Two preparations of myelin basic protein (MBP) were derived from an acid excretion of chloroform-methanol defatted bovine spinal cord. The first was purified by ion-exchange chromatography using guanidine-HCl; the second, by high performance liquid chromatography (HPLC) using a triethylamine eluant. Both methods of preparation yield MBP which is identical on acid-urea polyacrylamide gel electrophoresis and which has identical encephalitogenic potency. Because of the greater time-efficiency of the HPLC system with no deleterious side effects due to buffer contamination, this latter method can be recommended for MBP purification.     

The major site of guinea-pig myelin basic protein encephalitogenic in Lewis rats.

In the Lewis rat, fragment 43–88 of the highly encephalitogenic guinea-pig basic protein has been previously shown to retain the full activity of the parent protein. In the present studies this fragment was subjected to controlled chymotryptic digestion so that cleavage occurred only at tyrosine 67, generating two peptides, residues 43-67 and residues 68-88. When compared on an equimolar basis peptide 68-88 had the same encephalitogenic activity as the intact fragment and induced the same degree of immunologically specific cell response as measured by the in vitro lymphocyte stimulation test. Peptide 68-88 was further fragmented by selective tryptic cleavage at arginine 78 after blocking lysine 73 with citraconic anhydride. The two peptides, residues 68-78 and residues 79-88, were not encephalitogenic, indicating that residues adjacent to the point of cleavage contribute to the active site.     

Treatment of an encephalitogenic peptide from guinea pig myelin basic protein with alpha-protease and thermolysin. Isolation of fragments and determination of cleavage sites.

Two peptic fragments (residues 37-88 and 43-88) of guinea pig myelin basic protein which are capable of inducing experimental allergic encephalomyelitis in Lewis rats were cleaved to shorter fragments with alpha-protease (Crotalus atrox proteinase, EC 3.4.24.1) and thermolysin (EC 3.4.24.4). The fragments were isolated, purified, and identified by amino acid composition and NH2- and COOH-terminal residues. The time courses of the reactions, monitored by thin layer electrophoresis of the digests, showed that alpha-protease cleaves peptide (43-88) initially at the Pro(71)-Gln(72) bond, and that the product peptides are subsequently attacked at the Arg(63) -Thr(64), Ser(74)-Gln(75), Arg(78)-Ser(79), and Ser(76)-Gln(80) bonds. No significant cleavages occurred at the -Leu, -Val, and -Ala bonds. These results are in striking contrast to those obtained previously by others workers with other peptide substrates, where selective cleavage at hydrophobic residues occurred. Thermolysin was found to attack peptide (37-88) at the Phe(42)-Phe(43) bond very rapidly; the product peptides were subsequently attacked at the His(60)-Ala(61), Ser(38)-Ile(39)-Tyr(67)-Gly(68), and Pro(84)-Val(85) bonds. These cleavages are compatible with the known specificity of this enzyme. Several of the fragments prepared with these two enzymes, peptides (43-71), (61-88), (75-88), and (72-84) have been used in other studies to locate the encephalitogenic site in the parent peptic peptide.     

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.This work supported at Duke University Medical Center by Research Grant NS-10237 from the National Institutes of Health of the U.S. Public Health Service and the Medical Scientist Training Program Grant #5-T32-OMO-7171-08; at St. Luke's Hospital Center by NS-15322 from the National Institutes of Health of the U.S. Public Health Service; and at Northwestern University by Research Grant NS-06262 from the National Institutes of Health of the U.S. Public Health Service.     

Homologous sequences in cholera toxin A and B subunits to peptide domains in myelin basic protein

Recent reports that myelin basic protein (MBP) can be ADP-ribosylated and contains specific sites that bind GTP and GM1 ganglioside, have suggested an analogy to the properties of cholera toxin. Comparisons of pairs of sequences between these two proteins yielded two regions of homology between MBP and the cholera toxin B (chol B) subunit, and one region of homology with the cholera toxin A (chol A) subunit. The matching sites within chol B consisted of a 17 amino acid residue sequence (residues 30-46 in chol B and residues 102-118 in human-MBP, hMBP, p less than 0.0007) and an 11 residue span (residues 31-41 in chol B and sequence 29-39 in hMBP, p less than 0.0004). The homologous site within chol A corresponded to an 11 residue span (residues 130-140 in chol A and 67-77 in hMBP sequence, p less than 0.00007). Since portions of the cholera toxin sequence are virtually identical to sections of the sequence in E. coli toxin, the homology is also valid for the same sequences in this toxin. The highly antigenic behavior of MBP that is related to the induction of experimental allergic encephalomyelitis may be paralleled by comparable neural pathology from the homologous regions of cholera toxin.     

Experimental allergic encephalomyelitis: sequestered encephalitogenic determinant in the bovine myelin basic protein.

The presence of a sequestered encephalitogenic determinant for Lewis rats in the bovine myelin BP was demonstrated with synthetic peptide sequences prepared in our laboratory by the Merrifield solidphase method. The sequence of the encephalitogenic determinant (residues 75-84) from bovine BP (peptide S6), H-Ala-Gln-Gly-His-Arg-Pro-Gln-Asp-Glu-Asn-OH, is similar but not identical to the sequence reported for the guinea pig BP (peptide S53), H-Ser-Gln-(–)-(–)-Arg-Ser-Gln-Asp-Glu-Asn-OH. The presence or the absence of Gly-His from the sequence of either the bovine or the guinea-pig determinants did not alter their encephalitogenic potencies; however, the presence of Gly-His at positions 77 and 78 together with H-Gly-Ser-Leu-Pro-Gln-Lys- (residues 69-74) at the N-terminal end of the bovine determinant destroyed its encephalitogenic potency. In contrast to the absence of Gly-His from the potent encephalitogenic guinea-pig BP, guinea-pig fragment 44-89, and synthetic peptide S49, its presence in the bovine sequence prevents recognition of this determinant and renders the parent bovine BP, bovine fragment 44-89, and synthetic peptide S8 (residues 69-84) relatively non-encephalitogenic. The results of this study suggest that intramolecular interactions occur between adjacent amino acids, conferring secondary or tertiary structures upon this region of the bovine BP which renders the encephalitogenic determinant inaccessible for recognition by the host animal. The presence of sequestered disease-inducing determinants needs to be considered in choosing a particular BP for therapeutic use.     

A fusion protein consisting of IL-16 and the encephalitogenic peptide of myelin basic protein constitutes an antigen-specific tolerogenic vaccine that inhibits experimental autoimmune encephalomyelitis

To test a novel concept for the generation of tolerogenic vaccines, fusion proteins were constructed encompassing a tolerogenic or biasing cytokine and the major encephalitogenic peptide of guinea pig myelin basic protein (GPMBP; i.e., neuroantigen or NAg). The cytokine domain was predicted to condition APC while simultaneously targeting the covalently linked encephalitogenic peptide to the MHC class II Ag processing pathway of those conditioned APC. Rats were given three s.c. injections of cytokine-NAg in saline 1-2 wk apart and then at least 1 wk later were challenged with NAg in CFA. The rank order of tolerogenic activity in the Lewis rat model of EAE was NAgIL16 > IL2NAg > IL1RA-NAg, IL13NAg >or= IL10NAg, GPMBP, GP69-88, and saline. NAgIL16 was also an effective inhibitor of experimental autoimmune encephalomyelitis when administered after an encephalitogenic challenge during the onset of clinical signs. Covalent linkage of the NAg and IL-16 was required for inhibition of experimental autoimmune encephalomyelitis. These data identify IL-16 as an optimal cytokine partner for the generation of tolerogenic vaccines and indicate that such vaccines may serve as Ag-specific tolerogens for the treatment of autoimmune disease.     

Peptides of myelin basic protein are encephalitogenic in rats without the aid of emulsions.

Immunization with peptides is usually done with the aid of Freund's adjuvant. Using peptides derived from myelin basic protein, we show that aqueous solutions can be antigenic (encephalitogenic in this instance) in Lewis rats. The first procedure involved multiple doses of aqueous peptide, increased absorption into the lymphatic system from the peritoneal cavity in the postinflammatory state, and the use of pertussis vaccine. Three different peptides containing the major encephalitogenic site were active in this system, with the activity somewhat proportional to the size of the fragment. The second procedure, the direct delivery of peptide to lymph nodes by percutaneous inoculation, was equally successful and did not require the use of pertussis vaccine.