Tumor necrosis factor receptor-1 (TNFR1, CD120a) has been implicated in the pathogenesis of several experimental models of T cell-mediated autoimmune disorders, but its role in antibodymediated autoimmune diseases has not been addressed. Experimental autoimmune myastheniagravis (EAMG), an autoantibody-mediated T cell-dependent neuromuscular disorder, representsan animal model for myasthenia gravis in human. To investigate the role of TNFR1 in thepathogenesis of EAMG, TNFR1-/- and wild-type mice were immunized with Torpedo acetylcholinereceptor (AChR) in complete Freund's adjuvant. TNFR1-/- mice failed to develop EAMG. Lymphoidcells from TNFR1-/- mice produced low amounts of Th1 (IFN-γ, IL-2 and IL-12)-type cytokines, butelevated levels of Th2 (IL-4 and IL-10)-type cytokines compared with lymphoid cells of wild-typemice. Accordingly, the levels of anti-AChR IgG2 antibodies were severely reduced and the level ofanti-AChR IgG1 antibodies were moderately reduced. Co-injection of recombinant mouse IL-12 withAChR in adjuvant restored T cell responses to AChR and promoted development of EAMG inTNFR1-/-mice. These results demonstrate that the TNF/TNFR1 system is required for thedevelopment of EAMG. The lack of a functional TNF/TNFR1 system can, at least in part, besubstituted by IL-12 at the stage of initial priming with AChR and adjuvant. Introduction.

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.

Experimental autoimmune myasthenia gravis (EAMG) is an animal model for human myasthenia gravis (MG). Autoantibody-induced functional loss of nicotinic acetylcholine receptor (AChR) at the postsynaptic membrane is an important pathogenic feature of both MG and EAMG. To evaluate the extent at which the humoral immune response against AChR operates in the pathogenesis of EAMG, we immunized B cell knockout (mMT) and wild-type C57BL/6 mice with AChR and complete Freund’s adjuvant. The ability of AChR-primed lymph node cells to proliferate and secrete IFN-g in response to AChR and its dominant peptide a146-162 were intact in mMT mice as in wild-type mice. Similar amounts of mRNA for IFN-g, IL-4 and IL-10 in AChR-reactive lymph node cells were detected in mMT and wild-type mice. However, mMT mice had no detectable anti-AChR antibodies and remained completely free from clinical EAMG. We conclude that B cells are critically required for the genesis of clinical EAMG, but not for AChR-specific T cell priming.

Tolerance to B cell-mediated experimental autoim-mune myasthenia gravis (EAMG), an animal model for myasthenia gravis (MG) in human s, can be achieved byn asal adminis tra tion of the autoantigen acetylcholin ereceptor (AChR). Nasal tolerance induction requiresonly l/1000 0f the amount of AChR used for oral toler-ance in ductio n, but is as effe ctive in preventing EAMG.To investigate whether nasally induced tolerance toEAMG can be inOuenced by nasal administration ofcytokin es, recom bin ant rat IFN -y (total 5000 U/ra t), acombination of AChR and IFN-'y or AChR alone was given nasally to Lewis rats before immunization withAChR and complete Freun d's adjuvant (CFA). One ad-ditional group of rats received the same amount ofAChR nasally in conjunction with IFN-y (total5000 Ulrat) intraperitoneally. AChR given alone nasally in-duced effective tolerance to EAMG whereas rats re-ceiving AChR + IFN-y by the nasal route exhibited asimilar disease pattern, and similarly escalated T andB cell responses to AChR when compared to controlEAMG rats. In contrast, administration of IFN-y ip to-gether with AChR nasally did not affect the inductionof tolerance to EAMG. IFN-'y given alone nasally didnot affect clinic al EAMG. This study demonstrates th at nasal tolerance can be modulated by nasal administra-tion of minute amounts of IFN- y. Nas al adminis trationof certain cytokines with benemial effects mightbroaden the effectiveness of applying nasal toleranceas a poten tial therapeu tic means of preventing au toim-mune diseases..