Clonotypic analysis of anti-acetylcholine receptor antibodies produced against native and denatured antigen

Rats were immunized with either conformationally intact acetylcholine receptor (AChR) or reduced and sodium dodecyl sulfate (SDS)-denatured AChR. As expected, challenge with native AChR (nAChR) resulted in the production of serum antibodies reactive with native AChR; these antibodies were, as observed in earlier studies, oligoclonal, dominated by the rat IgG2a subclass, heterogeneous with respect to binding avidity, and importantly, able to interfere with normal AChR-dependent muscle contraction. Antibodies produced as a result of immunization with denatured AChR (dAChR) that were crossreactive with nAChR were similar but not identical to those produced directly against nAChR; in contrast, however, dAChR-stimulated antibodies were clearly incapable of causing detectable impairment of AChR-dependent muscle contractile function. This difference in disease-causing potential was demonstrated in spite of the observation that either nAChR or dAChR could generate similar levels of circulating antibodies that reacted with the native form of AChR. Moreover, the same difference in disease-causing potential was again observed upon passive intravenous administration of anti-AChR antibodies into naive recipient rats. IEF analyses demonstrated that antibodies stimulated by dAChR immunization expressed the same clonotypic heterogeneity and isotype distribution as those stimulated by nAChR immunization. However, an apparent shift was observed in the preferred clonotypes expressed in rats immunized with dAChR; antibodies with relatively lower binding avidities were more markedly represented than the higher avidity antibodies commonly accompanying immunization with nAChR. Furthermore, a distinct subset of high avidity clonotypes was expressed following immunization with dAChR not associated with nAChR immunization.