Dysregulation of B Cell Repertoire Formation in Myasthenia Gravis Patients Revealed through Deep Sequencing

Abstract

<p class="first" id="P1">Myasthenia gravis (MG) is a prototypical B cell-mediated autoimmune disease affecting 20–50 per 100,000 people. The majority of patients fall into two clinically distinguishable types based on whether they produce autoantibodies targeting the acetylcholine receptor (AChR-MG) or muscle specific kinase (MuSK-MG). The autoantibodies are pathogenic, but whether their generation is associated with broader defects in the B cell repertoire is unknown. To address this question, we performed deep sequencing of the B cell receptor repertoire of AChR-MG, MuSK-MG and healthy subjects to generate approximately 518,000 unique VH and VL sequences from sorted naïve and memory B cell populations. AChR-MG and MuSK-MG subjects displayed distinct gene segment usage biases in both VH and VL sequences within the naïve and memory compartments. The memory compartment of AChR-MG was further characterized by reduced positive selection of somatic mutations in the H-CDR regions and altered H-CDR3 physicochemical properties. The VL repertoire of MuSK-MG was specifically characterized by reduced V/J segment distance in recombined sequences, suggesting diminished VL receptor editing during B cell development. Our results identify large-scale abnormalities in both the naïve and memory B cell repertoires. Particular abnormalities were unique to either AChR-MG or MuSK-MG indicating that the repertoires reflect the distinct properties of the subtypes. These repertoire abnormalities are consistent with previously observed defects in B cell tolerance checkpoints in MG, thereby offering additional insight regarding the impact of tolerance defects on peripheral autoimmune repertoires. These collective findings point toward a deformed B cell repertoire as a fundamental component of MG. </p>