Inhibition of T cell proliferation specific for acetylcholine receptor epitopes related to myasthenia gravis with antibody to T cell receptor or with competitive synthetic polymers

Cytokine profile and T cell adhesiveness to endothelial selectins: in vivo induction by a myasthenogenic T cell epitope and immunomodulation by a dual altered peptide ligand

Myasthenia gravis (MG) is a T cell-regulated antibody-mediated autoimmune disease. Immunization with two myasthenogenic peptides, p195-212 and p259-271, that are sequences of the human acetylcholine receptor alpha subunit was shown to induce experimental autoimmune MG (EAMG)-associated immune responses. A peptide composed of the two altered peptide ligands (APL) of the myasthenogenic peptides (designated as dual APL) inhibited, in vitro and in vivo, those responses. The objectives of this study were to examine (i) whether in vivo T cell activation by p259-271 affects the cytokine profile and the T cell migration ability, and (ii) whether the latter are immunomodulated by in vivo administration of the dual APL. Our results showed that immunization of mice with p259-271 enriched the population of lymph node and spleen cells with subsets of T cells with strong adhesiveness towards E- and P-selectins. This enrichment was associated with an acquisition of a T(h)1-type cytokine profile. Treatment of the immunized mice with the dual APL interfered with both the migratory potential of the autoreactive T cells, and the production of the T(h)1-type cytokines IL-2 and IFN-gamma (known to play a pathogenic role in MG and EAMG). T cells derived from APL-treated mice acquired a T(h)3-type cytokine profile, characterized by the secretion of the immunosuppresive cytokine transforming growth factor-ss. Thus, our results suggest that T cell selectin ligands and T cell-derived cytokines are involved in the induction and immunomodulation of EAMG- and MG-associated T cell responses.

T cell receptor expression and differential proliferative responses by T cells specific to a myasthenogenic peptide

Myasthenia gravis (MG) is a T-cell-regulated autoimmune disease in which a pathological autoantibody response is mounted against the nicotinic acetylcholine receptor of the neuromuscular junction. Our laboratory previously identified a T cell epitope, p195-212, derived from the human acetylcholine receptor alpha subunit, which triggered PBL to proliferate from about 70% of MG patients tested. p195-212 was also found to be an immunodominant T cell epitope in SJL mice and a cryptic epitope in C3H.SW mice. Inoculation of naive SJL mice with cells from a p195-212-specific syngeneic T cell line caused MG-related autoimmune manifestations in those mice. In these studies we analyzed TCR alpha and beta chain sequences used by T cell lines and clones from both high- and low-responder mouse strains in response to p195-212. T cell lines generated from either strain expressed single TCR V beta gene segments (V beta 17 in SJL mice and V beta 8 in C3H.SW mice). By deleting V beta 17-expressing T cells in p195-212-immunized SJL mice we established a T cell line that expressed the V beta 6 gene product, suggesting that SJL mice are not limited to using a single V beta gene segment in response to p195-212. In addition, we found that N- and/or C-terminal-truncated peptides of p195-212, presented under the same culture conditions to different clones bearing the same TCR alpha beta chain, could elicit very different proliferative responses from the clones. Thus, even within a constrained system, factors other than TCR sequence contribute to the differential stimulation of T cell responses.

A peptide composed of tandem analogs of two myasthenogenic T cell epitopes interferes with specific autoimmune responses

Myasthenia gravis (MG) is a T cell-regulated, antibody-mediated autoimmune disease. Two peptides representing sequences of the human acetylcholine receptor alpha-subunit, p195-212 and p259-271, were previously shown to stimulate peripheral blood lymphocytes of patients with MG and were found to be immunodominant T cell epitopes in SJL and BALB/c mice, respectively. Single amino acid substituted analogs of p195-212 (analog Ala-207) and p259-271 (analog Lys-262) were synthesized. We showed that analogs Ala-207 and Lys-262 inhibited, in vitro and in vivo, the proliferative responses of T cell lines specific to the relevant peptide and lymph node cells of mice immunized to p195-212 and p259-271, respectively. To inhibit T cell responses to both peptides (p195-212 and p259-271), we synthesized dual analogs composed of the tandemly arranged two single (Ala-207 and Lys-262) analogs (dual analog) either sequentially (Ala-207-Lys-262) or reciprocally (Lys-262-Ala-207). In the present study, we report that both dual analogs could bind to major histocompatibility complex class II molecules on antigen-presenting cells of SJL and BALB/c mice. Analog Lys-262-Ala-207, which bound more efficiently to major histocompatibility complex class II molecules, was found to inhibit the proliferative responses of both p195-212- and p259-271-specific T cell lines. Furthermore, the analog inhibited the in vivo priming of lymph node cells of both SJL and BALB/c mice when administered i.v., i.p., or per os. The dual analog Lys-262-Ala-207 could also immunomodulate myasthenogenic manifestations in mice with experimental autoimmune MG induced by inoculation of a pathogenic T cell line. Thus, a single peptide that is composed of analogs to two epitope specificities can be used to regulate T cell responses and disease associated with each epitope.

Binding of peptides of the human acetylcholine receptor alpha-subunit to HLA class II of patients with myasthenia gravis

MG is an autoimmune disease in which T cells specific to T-cell epitopes of the human acetylcholine receptor play a role. We have identified two peptides, p195-212 and p259-271, of the human acetylcholine receptor alpha-subunit, to which PBLs of MG patients responded by proliferation. Nevertheless, proliferation assays are relatively complicated to perform and might be affected by medications taken by the patients. Therefore, we tested the possibility of using a different assay to determine recognition of these peptides by MG patients. Thus, we performed a direct binding assay using biotinylated peptides and APCs from peripheral blood of MG patients and healthy controls. With this assay we detected the binding of the two peptides to the surface of intact APCs of both MG patients and control donors. Moreover, the presentation of peptide p259-271 by individuals with MG was significantly higher than that observed in healthy subjects. The peptides were specifically bound to HLA class II determinants on the APCs, as shown by inhibition with antibodies to the HLA class II haplotypes of the individuals investigated. Moreover, the binding of these peptides was in correlation with their ability to induce specific proliferative responses of peripheral blood T cells of these patients. The ability to screen for potentially pathogenic epitopes in each patient is of importance for the future design of specific inhibitory analogues that might be used to treat MG.

In vivo preferential usage of TCR V beta 8 in Torpedo acetylcholine receptor immune response in the murine experimental model of myasthenia gravis

The aim of our study was to determine the T cell receptor (TCR) V beta gene usage involved in the T cell response to Torpedo AChR in C57BL/6 mice. The specific proliferation towards AChR was found to be blocked by anti-V beta 8.1,2,3 and to a lesser extent by anti-V beta 5 mAbs, but not by the other antibodies used (anti-V beta 2, V beta 6, V beta 9). In addition, a significant expansion of CD4+ V beta 8+ cells was observed when lymph node cells from these primed mice were stimulated in vitro with purified AChR. Involvement of V beta 8 subfamilies was also explored in vivo. After 7 days of treatment, there was a striking inhibition of the proliferative response of cells from anti-V beta 8.1,2,3-treated mice and a moderate inhibition when using anti-V beta 8.1,2 and anti-V beta 8.2 antibodies. Thus our in vitro and in vivo analysis indicate that in C57Bl/6 mice, T cell response to AChR is restricted to few V beta TCR, mostly belonging to the V beta 8 sub-families.

Protective immunity and granulomatous inflammation is mediated in vivo by T cells reactive to epitopes common to avirulent and listeriolysin-negative mutants of Listeria monocytogenes

The ability of several listeriolysin O-negative mutants of the EGD and NCTC 7973 strains of Listeria monocytogenes to activate specific T cell responses in vitro and in vivo was determined. T cell lines from different inbred mouse strains and derived T cell clones elicited by L. monocytogenes, strain EGD, which are able to adoptively transfer protection and granuloma formation were examined. Specificity testing revealed no differences between listeriolysin-positive and -negative strains to induce proliferation of the T cell lines and clones. Similar results were obtained when we examined CD4+ T cell-mediated granuloma formation in the livers of mice previously immunized with viable bacteria of the virulent strain. Granulomatous inflammation could be elicited by iv application of heat-killed bacteria of listeriolysin-positive and of -negative bacteria. Protective immunity to listerial infections and granulomatous inflammation therefore appears to be mediated by T cells recognizing epitopes on listerial antigens that are shared by both pathogenic and nonpathogenic Listeria strains.

Synthetic copolymer 1 inhibits human T-cell lines specific for myelin basic protein

Copolymer 1 (Cop 1) is a synthetic basic random copolymer of amino acids that has been shown to be effective in suppression of experimental allergic encephalomyelitis and has been proposed as a candidate drug for multiple sclerosis. Cop 1 is immunologically cross reactive with myelin basic protein (BP) and was shown to inhibit murine BP-specific T-cell lines of various H-2 restrictions. In the present study these findings were extended to include human T-cell lines. Cop 1 competitively inhibited the proliferative responses and interleukin 2 secretion of six BP-specific T-cell lines and 13 clones with several DR restrictions and epitope specificities. Conversely, BP inhibited--albeit to a lesser extent--the response of all the Cop 1-specific T-cell lines and clones, irrespective of their DR restrictions. Another random copolymer of tyrosine, glutamic acid, and alanine, denoted TGA, had no effect on these lines. Neither Cop 1 nor BP inhibited the response of lines and clones specific for purified protein derivative. Cop 1 and BP exerted their cross-inhibitory effects only in the presence of antigen-presenting cells. These results suggest that Cop 1 can compete with BP for the binding to human major histocompatibility complex molecules. In view of recent studies implicating BP reactivity in multiple sclerosis, these findings suggest a possible mechanism for the beneficial effect of Cop 1 in this disease.

Heat-killed Listeria monocytogenes and L. monocytogenes soluble antigen induce clonable CD4+ T lymphocytes with protective and chemotactic activities in vivo

In the present study we attempted to analyze the possibility to induce in mice a T-cell response using killed Listeria monocytogenes in adjuvant. Clearly, nonviable antigen is capable of inducing protective and granuloma-forming T cells in C57BL/6 mice when emulsified in complete Freund's adjuvant. These T cells were cloned in vitro by using antigen and irradiated splenocytes, as antigen-presenting cells, and the clones were characterized in vivo. Listeria-specific T-cell clones showed protective and chemotactic activity upon adoptive transfer, although some degree of functional heterogeneity among different clones was observed. The heterogeneous in vivo functions could not be correlated with the ability of the clones to produce gamma interferon or T-cell growth factor (interleukin-2 and/or interleukin-4). It was demonstrated that an in vivo relevant fraction of listeria-specific T lymphocytes can be induced by nonviable antigen in complete Freund's adjuvant. These results show that the low immunogenicity of heat-killed bacteria is not due to the expression of specific protective T-cell epitopes only by live bacteria.