Myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG) are caused by auto-antibodies against thenicotinic acetylcholine receptor (AChR) at the postsynaptic membrane. To evaluate the extent to which the humoral immune response againstAChR opcratcs in the pathogenesis of EAMG, we immunized B-cell knockout(儿MT) and wild type C57BL/6 mice with AChR in complete Freund's adjuvant. The ability of AChR-primed lymph node cells to proliferate and secreteIFN-/in response to AChR and itsdominant peptide a146-162 were intact in ktMT as in wild type mice. Similar levels of mRNA for IFN- IL-4 and IL-IO in AChR-reactivelymph node cells were detected in ktMT and wild type mice. However, htMT mice had no detectable anti-AChR antibodies and never devel-oped clinical EAMG. We conclude that B-cells are critically required for the genesis of clinical EAMG, but not for AChR-specific T-cellpriming

Autoantigen administration via nasal mucosal tissue can induce systemic tolerance more effectively than oral administration in anumber of experimental autoimmune diseases, including Ab-mediated experimental autoimmune myasthenia gravis, a murinemodel of myasthenia gravis. The mechanisms underlying nasal tolerance induction are not clear. In this study, we show that nasaladministration of acetylcholine receptor (AChR) in C57BL/6 mice, before immunizations with AChR in adjuvant, results in delayed onset and reduced muscle weakness compared with control mice. The delayed onset and reduced muscle weakness wereassociated with decreased AChR-specific lymphocyte proliferation and decreased levels of anti-AChR Abs of the IgG2a and IgG2bisotypes in serum. The clinical and immunologicalchanges in the AChR-pretreated C57BL/6 wild-type (wt) mice were comparable with those observed in AChR-pretreated CD82/2 mice, indicating that CD81 T cells were not requiredfor the generation of nasaltolerance. AChR-pretreated wt and CD82/2 mice showed augmented TGF-b and reduced IFN-g responses, whereas levels of IL-4were unaltered. Splenocytes from AChR-pretreated wt and CD82/2 mice, but not from CD42/2 mice, suppressed AChR-specificlymphocyte proliferation. This suppression could be blocked by Abs against TGF-b. Thus, our results demonstrate that the suppression induced in the present model is independent of CD81 T cells and suggest the involvementof Ag-specific CD41 Th3cells producing TGF-b.

Experimental autoimmune myasthenia gravis(EAMG) is caused by autoantibodies against the nicotinicacetylcholine receptor (AChR) at the neuromuscularpostsynaptic membrane and represents an animalmodel of myasthenia gravis in human. Recentstudies highlighted the roles of TH1 cytokines (IFN-g,IL-12), rather than TH2 cytokines (IL-4), in the pathogenesisof EAMG by using homozygous (2/2) knockoutmice with an EAMG-susceptible genetic background.To further evaluate a role for IFN-g, we injected recombinantrat IFN-g (rrIFN-g) at the time of immunizationwith AChR in complete Freund’s adjuvant toEAMG-susceptible Lewis rats and EAMG-resistantWistar Furth (WF) rats. RrIFN-g enhanced Lewis ratEAMG. The exacerbated muscular weakness was associatedwith higher levels of anti-AChR IgG and enhancedTNF-a responses. Anti-AChR IgG antibody levelswere augmented to a similar extent as in Lewirats, however, the identical immunization and IFN-ginjection induced only mild and transient EAMG inWF rats due to the default TH3 phenotype developmentand inherent low TH1 responses. We conclude that IFN-g plays a major role in the pathogenesis ofEAMG in the Lewis rat, but fails to break disease resistancein the WF rat.

CTLA-4 appears to be a negative regulator of T cell activation and is implicated in T cell-mediated autoimmune diseases.Experimental autoimmune myasthenia gravis (EAMG), induced by immunization of C57BL/6 mice with acetylcholine receptor(AChR) in adjuvant, is an autoantibody-mediated disease model for human myasthenia gravis (MG). The production of anti-AChR Abs in MG and EAMG is T cell dependent. In the present study, we demonstrate that anti-CTLA-4 Ab treatment enhancesT cell responses to AChR, increases anti-AChR Ab production, and provokes a rapid onset and severe EAMG. To address possible mechanisms underlying the enhanced autoreactive T cell responses after anti-CTLA-4 Ab treatment, mice were immunized withthe immunodominant peptide a146–162 representing an extracellular sequence of the AChR. Anti-CTLA-4 Ab, but not control Ab,treatment subsequent to peptide immunization results in clinical EAMG with diversification of the autoantibody repertoire as wellas enhanced T cell proliferation against not only the immunizing a146–162 peptide, but also against other subdominant epitopes.Thus, treatment with anti-CTLA-4 Ab appears to induce determinant spreading, diversify the autoantibody repertoire, andenhance B cell-mediated autoimmune disease in this murine model of MG.