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G A Hashim

Publications and source records attributed to G A Hashim.

At least 37 records · Page 2Linked to original sources
PubMed1990

Antibodies specific for VB8 receptor peptide suppress experimental autoimmune encephalomyelitis.

Recent studies from our laboratory have shown, for the first time, that a synthetic peptide from that TCR VB chain used preferentially by encephalitogenic T cells induced the formation of protective, MHC class I-restricted T cells and prevented the development of EAE in Lewis rats. In this report we 1) demonstrate that immunization with the TCR-VB8-39-59 peptide generated peptide-specific antibodies that protect against experimental autoimmune encephalomyelitis induced by either of the two distinct encephalitogenic epitopes of basic protein, and 2) characterize the production and biologic functions of rat and rabbit antibody responses to the TCR peptide. The antibodies in both species increased in titer over time, were highly specific for the immunogen by direct reaction and inhibition assays, stained only VB8+ T cells, and suppressed clinical signs and to lesser extent the number of histologic lesions of experimental autoimmune encephalomyelitis mediated by VB8+ T cells. Coupled with our previous work, these results indicate that both humoral and cellular responses to the TCR-VB8-39-59 peptide can contribute independent immunoregulatory effects on encephalitogenic T lymphocytes that use common V region genes in response to epitopes of myelin basic protein.

Amino Acid Sequence↗
PubMed1989

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.

Amino Acid Sequence↗
PubMed1989

T cell determinants of myelin basic protein include a unique encephalitogenic I-E-restricted epitope for Lewis rats.

The major encephalitogenic epitope for Lewis rats is the 72-89 sequence of guinea pig basic protein (GP-BP) or rat basic protein (Rt-BP). T cells responsive to this epitope are I-A restricted and preferentially express the V alpha 2:V beta 8 gene combination in their TCR. In this work, we describe for the first time the delayed appearance of T cells specific for additional discrete determinant of BP, the nonencephalitogenic 55-68 sequence of GP-BP restricted by I-A, and the encephalitogenic 87-99 sequence of Rt-BP restricted by I-E. The TCR V alpha 2:V beta 8 gene combination was expressed by both encephalitogenic GP-BP S72-89 and Rt-BP S87-99 T cell specificities but not by GP-BP 44-68-specific T cells. This is the first demonstration of I-E-restricted encephalitogenic T cells in Lewis rats and supports the conclusion that the I-E class II locus is involved in autoimmune diseases.

Amino Acid Sequence↗
PubMed1989

Two separate 18-amino acid domains of tau promote the polymerization of tubulin.

Tau is a heat-stable microtubule-associated protein which promotes tubulin polymerization. The assembly promoting region of tau was localized using synthetic peptides modeled after domains found in both human and mouse tau. The design of these synthetic peptides was based on the triple repeat motif found in mouse tau. The first peptide, Tau-(187-204), and the second peptide, Tau-(218-235), are capable of promoting the polymerization of tubulin into microtubules, at concentrations above 100 microM. Two other peptides tested, TauR and Tau-(250-267), were not able to promote the assembly of tubulin over a range of concentrations up to 800 microM. TauR is a random analog of Tau-(187-204). Although TauR is unable to promote polymerization, it can modify Tau-(187-204)-induced tubulin assembly.

Amino Acid Sequence↗
PubMed1989

Defective T helper cell epitope responsible for the failure of region 69-84 of the human myelin basic protein to induce experimental allergic encephalomyelitis in the Lewis rat.

Studies from our laboratory have shown that region 69-84 (synthetic peptide S49S) of myelin basic protein (MBP) defines an encephalitogenic sequence for experimental allergic encephalomyelitis (EAE) in Lewis rats. The most potent EAE inducers are the guinea pig MBP (Gp-MBP) and region 69-84, known as synthetic peptide Gp-S49S: (See text: formula). Human (H-MBP) was considerably less potent than Gp-MBP, and region 69-84 (H-S49S) of H-MBP did not induce hind leg paralysis or any histological signs of EAE. Since the development of EAE requires the expression of specific T and B cell epitopes, sequence analysis of H-S49S and Gp-S49S revealed phylogenetic variations in the H-S49S sequence, characterized by positions 77 and 78, and substitution of Ser with Thr at position 80: (See text: formula). Like Gp-S49S, peptide H-S49S induced the formation of antibodies with specificities directed against the C-terminal of the H-S49S, Gp-S49S, and homologous sequences. In contrast to Gp-S49S, neither II-S49S nor shorter peptides induced clonal T cell expansion when either of the peptides was added to encephalitogenic T cell clone D in culture. Clone D, which expresses T helper phenotype, was selected from encephalitogenic peptide-primed Lewis rats. The results of the study show that the failure of H-S49S to induce EAE is related to sequence alterations in the T helper cell epitope but not in the B cell epitope located in the N- and C-terminal portions of the S49S sequence, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1988

Encephalitogenic T cell clones with variant receptor specificity.

We explored antigenic differences between guinea pig (GP)-basic protein (BP), rat (Rt)-BP, and respective peptides from the encephalitogenic region for Lewis rats by comparing the fine specificity of T lymphocyte lines and clones selected from animals primed with these Ag. Encephalitogenic T cell lines specific for GP-BP or Rt-BP predictably recognized the corresponding 72-89 and to a lesser degree the 72-84 (S55S) amino acid sequence. T cell lines selected from rats primed with GP-S55S responded preferentially to GP-S55S compared to other peptides. A T cell line raised to Rt-S55S, however, initially recognized the S55S and S72-89 peptides but were nearly unresponsive to the intact GP-BP or Rt-BP. T cell clones selected from the Rt-S55S line at that point had two distinct patterns of response: clones that recognized both of the BP and the S55S peptides adoptively transferred delayed-type hypersensitivity and experimental autoimmune encephalomyelitis. These clones also recognized residues 69-81 (S67) but not peptide S75-89. In contrast, T cell clones that responded only to synthetic peptides GP-S55S and Rt-S55S but not to the parent BP adoptively transferred delayed-type hypersensitivity but not disease in Lewis rats. The same clones failed to respond to either the S67 or the S75-89 sequences. These results demonstrate that the encephalitogenic Rt-S55S sequence houses a minimum of two T cell epitopes with differing specificities and functions. One epitope is immuno-dominant and resembles the encephalitogenic region of the intact BP molecule. The second non-encephalitogenic epitope is restricted to the S55S sequences and is not shared by the parent BP, the S67, or the S75-89 sequences. Both types of Rt-S55S-specific clones differ in fine specificity from encephalitogenic clones selected from GP-BP immunized rats, thus indicating that uniformity of T cell recognition of the encephalitogenic epitope is not an absolute condition for T cells to be encephalitogenic.

Amino Acid Sequence↗
PubMed1988

Alpha-toxin binding to acetylcholine receptor alpha 179-191 peptides: intrinsic fluorescence studies.

Interactions between two alpha-toxins and the synthetic peptides alpha 179-191 from both calf and human acetylcholine receptor alpha-subunit sequences have been studied by measurements of quenching of intrinsic fluorescence after toxin addition. Dissociation constants of approx. 5 x 10(-8) M for binding of calf peptide by both alpha-cobratoxin and erabutoxin a have been estimated. The binding of alpha-cobratoxin to calf peptide, which leads to marked quenching of fluorescence intensity, is inhibited by a 10(4) molar excess of acetylcholine. The human alpha 179-191 peptide binds to alpha-cobratoxin, but not, under comparable conditions, to erabutoxin a.

Animals↗
PubMed1988

Human T-cell response to myelin basic protein in multiple sclerosis patients and healthy subjects.

In order to explore the T-cell repertoire to myelin basic protein (BP) of both multiple sclerosis (MS) patients and healthy subjects (HS), we raised BP reactive T-cell lines from blood mononuclear cells of eight MS patients and five HS. These lines were triggered in vitro by human BP. When analyzing their patterns of recognition of human BP versus heterologous BP, we could observe differences between healthy subjects and MS patients. Whereas T-cell lines from healthy subjects developed a response to heterologous BP, which was in most cases equal or higher than that elicited by human BP, T-cell lines from most MS patients displayed a low response, or no response at all, to one or several of the heterologous BP tested. A low response to bovine BP was only observed in active cases, whereas decreased responses to rat and/or monkey BP were observed both during remission and during active disease. This may indicate that T-cell repertoire to BP in MS patients differs from that of healthy subjects. BP-reactive T-cell clones were obtained by limiting dilution from two healthy subject lines. Their pattern of response to heterologous BP as compared to human BP suggest that T-cells from the same individual can recognize different BP epitopes.

Animals↗
PubMed1988

Role of antibodies in T cell-mediated experimental allergic encephalomyelitis.

The role of the humoral phase of the immune response in development of T cell-mediated experimental allergic encephalomyelitis (EAE) had not been clearly defined previously even though studies of the myelin basic protein (MBP) molecule had demonstrated the presence not only of T cell but also B cell epitopes capable of inducing cell-mediated immunity and antibody formation. Particularly relevant to this report are the immunological expressions of the region which induces EAE in the Lewis rat. The development of primary demyelination in Lewis rats is preceded by a cell-mediated immune response as well as antibody formation, both of which are highly specific to the encephalitogenic 14-residue peptide that defines the 69-84 region of the parent MBP. Our results are consistent with the dogma that EAE is a T cell-mediated disease, but they also clearly demonstrate an important role for specific antibodies in the development of these T cells responsible for demyelination. The antibody response, which may be heteroclitic, is necessary for T cells to develop into an effector T cell subset. Without this B cell response the subsequent T cell response does not lead to demyelination. In this report we shall discuss these findings and further show that the T cell and B cell epitopes, which are located within the 14-residue sequence, are physically separated and dependent upon the form of synthetic peptides known to induce T cell-mediated and/or humoral immunity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

Receptors for nerve growth factor on rat spleen mononuclear cells.

Considerable evidence is mounting to support the concept of a modulatory role for the brain and neuroendocrine system on the immune response. This neuroimmunomodulation occurs in part through the interaction of specific neurosubstances with receptors on lymphocytes and monocytes. Nerve growth factor (NGF) is a neuronotrophic factor necessary for the development and maintenance of sympathetic and embryonic sensory neurons. This trophic effect is initiated through binding of NGF at specific cell surface receptor sites on NGF-responsive cells. Several recent studies suggest that NGF may interact with cells of the immune system and may play a role in the regulation of some immunologic reactions. In this study we report on the presence of specific receptors for NGF on the surface of mononuclear cells from rat spleens. The NGF-binding sites are of the low-affinity type with Kd's in the 10(-9) M range. These receptors migrate on SDS-PAGE as two molecular species of approximately 190 and 125 kilodaltons. Our findings of receptors for NGF on lymphocytes and accessory cells support other evidence that NGF may influence immunoreactivity in vivo.

Animals↗
PubMed1987

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)

Amino Acid Sequence↗
PubMed1987

The polyclonal antibody responses of Lewis rats to the synthetic encephalitogenic neuropeptide S55S (residues 72-84 of guinea pig myelin basic protein) and its analogs.

Immunochemical analysis of polyclonal antisera from Lewis rats immunized with peptide analogs and subpeptides of residues 72-84 of guinea pig myelin basic protein (MBP) indicated that there were four main epitopic specificities involved: one represented by residues 76-80, one by residues 72-74, one by 81-84-Gly, and one involving 74-76 in a heteroclitic way even when the immunogen contained a tetraleucine spacer between residues 74 and 75. The affinities were all relatively low, ranging from 3 x 10(4) M-1 to 7.2 x 10(6) M-1, and each affinity population was very restricted with respect to heterogeneity. The results were commensurate with our hypothesis that autoimmune responses to homologous encephalitogenic neuropeptide determinants reflect an evolutionarily imposed degeneration of the overall response, and were also in agreement with our hypothesis that the affinities of autoantibodies against epitopes in the molecular neighborhood of an encephalitogen would be necessarily low. It was also found that peptide 69-81-Gly (S67) in solution would not interact in liquid phase radioimmunoassays with any of the above antibody populations, thus indicating that its preferred conformation did not allow the expression of autoreactive epitopes. There was no evidence that S67 in solution. even in the presence of S53, would express any epitopes reactive with autoantibodies. How this finding for a B cell product correlates with T cell-mediated immunologic responses is not totally understood, but it will be recalled that S67 by itself does not induce T cell-mediated experimental allergic encephalomyelitis (EAE), that S53 (residues 75-84-Gly) induces only clinical symptoms of EAE without attendant pathological disease, but that the two together induce classical EAE.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1987

A major epitope of synthetic rabbit encephalitogen S24 disclosed through the use of a tritiated peptide probe.

The antibody recognition of synthetic rabbit encephalitogen S24 (TTHYGSLPQKG), which had been inactivated by extensive iodination, was fully restored by tritium-iodine exchange during boron hydride reduction. A highly active form of 3H-S24 was obtained by reverse-phase high-performance liquid chromatography (HPLC) purification of the crude product and could be further separated into three continuous subfractions, the latter two of which were fully active from an immunochemical point of view. A major epitope was disclosed through use of the 3H-S24 probe, which required the intact S24 peptide for its expression. Confirmation of two linear epitopes previously encountered, GSLPQK and THYGSL, was also obtained, the latter through the use of the third HPLC subfraction of 3H-S24.

Animals↗
PubMed1987

Immunochemical specificity of antisera raised against the synthetic encephalitogenic peptide SH624, residues 59-74 of the myelin basic protein.

Synthetic peptide SH624 (SHHPARTAHYGSLPQK), residues 59-74 of human myelin basic protein (MBP) was found to be encephalitogenic in the rabbit. Four antisera raised, against the peptide were employed in a liquid-phase equilibrium competitive radioimmunoassay with a series of synthetic peptide analogs of the region to probe the structural requirements of the B-cell determinant subsumed within SH624. The cross-reactivities of the four antisera with intact MBP were also examined. Immunochemical analyses of the four antisera suggested specificities directed against a conformational determinant dependent upon residues from the more phylogenetically conserved carboxyl C-terminal region, residues 65-74 (TAHYGSLPQK) of the synthetic immunogen. Peptide analogs shorter than SH624 from the C-terminal end showed no cross-reactivity with any of the reagent antisera while analogs shorter from the N-terminal end and including the encephalitogenic sequence TTHYGSLPQK, as well as, HYGSLPQK were reactive under equilibrium competitive conditions. SH624-reactive antibodies, cross-reactive with purified heterologous MBPs from 10 different species were also identified in all four reagent antisera. The results of these experiments support previous investigations demonstrating the accessibility of the encephalitogenic 65-74 region in intact MBP. They also underscore the importance of B-cell recognition of organ specific antigenic determinants with respect to MBP immunology and, in particular, the recognition of autoreactive determinants in the neighborhood of encephalitogenic centers.

Animals↗
PubMed1987

Demyelinating disease: an immunological model for studies of neural antigens.

Studies have shown that the parent myelin basic protein (MBP) is a more potent antigen than its disease-inducing fragments. Based on equimolar ratios, 10-15 times more peptide is required to induce experimental allergic encephalomyelitis (EAE) with the same severity as that induced by the intact MBP. In this report, we show that 2 epitopes are required for EAE in Lewis rats; that which induces T cell-mediated immunity requires the expression of a B cell epitope for the development of full spectrum of clinical and histopathological signs of disease. Thus, the development of disease may be related to the magnitude of the humoral and cellular responses to particular B and T cell epitopes. Whether more than 1 epitope, over 30 of which have been located in the MBP, contribute to the development of MBP-induced disease is not clear; but what is clear is that the EAE-inducing peptide sequence, unlike the MBP, is restricted in terms of the number of recognizable epitopes.

Amino Acid Sequence↗
PubMed1986

Substrate specificity of rat brain calcium-activated and phospholipid-dependent protein kinase.

A synthetic peptide ArgThrProProProSerGly with sequence similar to the threonine sites of phosphorylation in both myelin basic protein and simian virus 40 T antigen could be phosphorylated in vitro by a purified rat brain Ca2+-activated and phospholipid-dependent protein kinase, protein kinase C. The apparent Km and Vm values of this heptapeptide for the enzyme were determined to be 240 microM and 60 nmol/min/mg, respectively. Up to 0.8 mol 32P could be incorporated into the peptide, mainly at the threonine residue. Substitution of the L-threonine residue in the heptapeptide by its D-enantiomer abolished the phosphorylatability of the peptide by protein kinase C. However, this (D)Thr-containing peptide could act as a competitive inhibitor for the kinase with an apparent Ki value of approximately 320 microM. These findings suggest that a triprolyl sequence may act as a recognition site for protein kinase C.

Animals↗