Neonatal tolerance to an immunodominant T cell reactivity does not confer resistance to EAMG induction in Lewis rats

The overall goal of this study was to determine, during induction of experimental autoimmune myasthenia gravis (EAMG) in Lewis rats, the relative importance of acetylcholine receptor (AChR)-reactive helper T cells associated with one particular immunodominant fine specificity. Thus, experiments presented below were designed to evaluate the immunopathological role played by helper T cells with reactivity against the AChR alpha subunit region associated with amino acid residues 100-116 (i.e., alpha 100-116); in particular, the relationship between T cell reactivity with this specificity and disease induction was assessed. In order to examine the importance of this T cell reactivity, Lewis rat neonates were made T cell tolerant to a synthetic peptide alpha 100-116 and subsequently evaluated for anti-AChR antibody production and resulting neuromuscular dysfunction. Results indicated that although T cell reactivity against the alpha 100-116 peptide could be effectively removed from the Lewis T cell repertoire, tolerized Lewis rats immunized with AChR could undergo an active anti-AChR antibody response that produced symptoms of EAMG. Thus, other AChR T cell reactivities appeared capable of providing adequate help to B cells leading to production of anti-AChR antibodies with pathogenic potential.

Examination of characteristics that may distinguish disease-causing from benign AChR-reactive antibodies in experimental autoimmune myasthenia gravis

In summary, the strategies of the experimentation described above were designed to address the confusion resulting from observations concerning the lack of correlation between antibody titers and disease severity in MG patients. Lessons learned from these studies of EAMG suggest that if the proportion of the total expressed/produced anti-AChR antibody repertoire with disease-causing potential differs from patient-to-patient with MG, then assessment of the total antibody titer becomes meaningless unless a particular patient produces disease-causing reactivities that make up a major portion of the total titer. Not only may disease severity depend on the titer of a small subset of disease-causing antibody(s) reactive with a particular conformation-dependent AChR region, but may also depend on the relative contribution of additional subsets of antibody with functionally irrelevant or potentially protective activity. The key to exploiting the existence of antibody subsets with differing disease-causing potential will be to create probes that would allow the easy monitoring of the relevant reactivities. For instance, carefully selected anti-idiotypic antibodies (such as the 11E10 monoclonal antibody described above) may be of great value when specifically capable of recognizing idiotypes that are selectively associated with disease-causing anti-AChR antibodies and under-represented on antibodies lacking disease-causing capability. If, in addition, characteristics of helper T cells are identified that allow more accurate prediction of D+ Id production, exciting opportunities would become available to more directly evaluate disease mechanisms and to develop more highly efficacious immunotherapeutic strategies.

Antigen presentation and T cell specificity repertoire in determining responsiveness to an epitope important in experimental autoimmune myasthenia gravis

The overall goal of this study was to define, in experimental autoimmune myasthenia gravis (EAMG), immunological differences between helper T cells from two inbred rat strains that explain disease susceptibility on the one hand (in Lewis rats) and disease resistance on the other hand (in Wistar Furth rats). The working hypothesis for these studies was that the T cell compartment in Wistar Furth rats may lack the ability to activate responsiveness by existing B cells that have the potential to produce disease-causing antibodies; this quality may be related to a lack of T cell reactivity toward a determinant(s) associated with the alpha subunit sequence alpha 100-116 of the acetylcholine receptor (AChR) that demonstrates immunodominance in Lewis rats. Results presented below are consistent with the conclusion that there is a deficit in the Wistar Furth (WF) T cell specificity repertoire responsible for unresponsiveness to this important AChR epitope; this deficit exists despite the apparent ability of WF antigen presenting cells to bind and present the alpha 100-116 peptide, and is likely responsible for the inability of Wistar Furth T cells to drive an anti-AChR antibody response with disease-causing potential.