Molecular Determinants of Pathogenic Autoantibodies in Autoimmune Myasthenia Gravis

Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Immunobiology

First Advisor

O'Connor, Kevin

Abstract

B cells, and the antibodies they produce, constitute a critical component of immune defense against a wide range of foreign pathogen challenges. However, glitches in the adaptive immune system are not uncommon, and if left unchecked could lead to an unwanted manifestation of self-reactivity and autoimmune pathogenesis. A rise in new-onset autoantibody disorders motivates improved understanding of the pathomechanisms involved in such diseases. Identification of disease-relevant human autoantibodies has the potential to uncover how autoreactive clones emerge, and the precise molecular mechanisms in which they elicit pathogenesis. Myasthenia gravis (MG) is an ideal human disease model for studying humoral autoimmunity as the autoantibodies are unequivocally pathogenic. MG autoantibodies most commonly target the nicotinic acetylcholine receptor (AChR), a membrane-bound ionotropic receptor responsible for neuromuscular transmission. Disruption of AChR impairs muscle contraction, and leads to muscle weakness that can progress to respiratory failure and paralysis. Upon binding AChR, autoantibody pathogenesis ensues via three distinct molecular mechanisms: complement activation, receptor blockade, and receptor internalization. The precise molecular autoantibody features that orchestrate these pathomechanisms are incompletely understood, but are of great investigative interest, and immense translational significance. Clinical disease outcomes in MG are remarkably heterogenous, and some patients are refractory to current treatments. This variability suggests an unrecognized heterogeneity of disease mechanisms between patients. We attribute these disparities to the underlying immunomolecular diversity of AChR autoantibody clones that differentially drive pathology in MG patients.This dissertation is a culmination of my graduate research work investigating the molecular determinants of pathogenic autoantibodies in AChR MG. To accomplish this, we sought to identify human monoclonal autoantibodies (mAb) from MG patients and inspect them based on their sequence, structure, and function. Chapter 1 provides an overview of the methodologies used to generate and functionally characterize a library of 19 human-derived AChR-specific recombinant mAbs, highlighting their divergent mechanisms for MG pathology, assessed through cell-based assays. Chapter 2 deciphers the relationship between structure and function through CryoEM of human adult AChR, resolving the atomic-level molecular interactions and spatial orientations of pathogenic mAbs. Chapter 3 examines the relationship between sequence and function through the molecular analyses of affinity-matured and class-switched IgG sequences, elucidating the immunomechanisms that improve autoantibody pathogenicity. Overall, our work here provides a detailed molecular framework for autoantibody pathogenicity, providing clues for how autoreactive clones emerge and develop in compromised immune systems. This dissertation outlines the major key components that orchestrate autoantibody pathogenesis which will guide the design of future therapeutic interventions for MG and similar autoantibody-mediated diseases.

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