Biology subjects

O'Connor, K. C.

Publications and source records attributed to O'Connor, K. C..

5 recordsLinked to original sources

bioRxiv2025

B Cell Tolerance and BCR Signaling Dysregulation in NF155-Mediated Autoimmune Nodopathies

ObjectiveAutoimmune nodopathies (AINs) are a group of rare, acquired autoimmune neuropathies with distinct clinical features and the presence of circulating autoantibodies - often of the immunoglobulin G4 (IgG4) subclass - targeting proteins at the node of Ranvier. Defects in B cell tolerance checkpoints have been implicated in several autoimmune diseases. Prior work identified defective B cell tolerance--reflected by a high frequency of self-reactive naive B cells--in patients with MuSK-positive myasthenia gravis (MG), mediated by IgG4 autoantibodies. Here, we investigated whether tolerance defects exist in neurofascin-155-mediated AIN (NF155-AIN), similar to MuSK+ MG. Additionally, we analyzed B and T cell transcriptomics and interactions at the single-cell level to explore the underlying pathomechanism. MethodsUsing a well-established assay, we assessed B cell tolerance fidelity by generating recombinant antibodies from new emigrant (NE) and mature naive (MN) B cell populations-- directly downstream of key tolerance checkpoints--from three NF155-AIN patients, and testing these antibodies for polyreactivity and autoreactivity, thereby determining the frequency of polyreactive and autoreactive B cells. The transcriptome of peripheral blood mononuclear cells (PBMC) was studied, with a special focus on naive B cells and CD4+ T cells at the single-cell level, along with characterization of cell-cell interactions. ResultsNF155-AIN patients have an elevated frequency of polyreactive B cells in the NE (37.4% compared to 9.7% in healthy controls (HCs), p = 0.03) and MN (31.5% compared to 10.5% in HCs, p = 0.03) compartments with increased B cell clones expressing autoreactive antibodies, consistent with a breach in early tolerance checkpoints. We observed abnormal B cell receptor (BCR) signaling characterized by low CD79B, CSK, BLNK, and BTK expression, which may contribute to a breach in B cell tolerance. We also observed evidence of impaired follicular helper T cells (Tfh) and regulatory T cells (Treg), which may limit the normal development and suppression of autoreactive B cells. Moreover, comparative gene expression analysis of B cells and CD4+ T cells from three patients with chronic inflammatory demyelinating polyneuropathy (CIDP) --a related autoimmune neuropathy-- confirmed that these differences are largely specific to NF155-AIN, supporting a distinct pathophysiology in this subset. ConclusionThese findings demonstrated a breach in early B cell tolerance checkpoints, defective BCR signaling, and disrupted T cell-B cell interactions in NF155-AIN, all of which may contribute to the development of pathogenic autoreactivity. These immunologic abnormalities appear distinct from those seen in CIDP, supporting NF155-AIN as a unique immunopathologic entity.

neuroscience↗

bioRxiv2024

Autoimmune mechanisms elucidated through muscle acetylcholine receptor structures

Skeletal muscle contraction is mediated by acetylcholine (ACh) binding to its ionotropic receptors (AChRs) at neuromuscular junctions. In myasthenia gravis (MG), autoantibodies target AChRs, disrupting neurotransmission and causing muscle weakness. Despite available treatments, patient responses vary, suggesting pathogenic heterogeneity. Current information on molecular mechanisms of autoantibodies is limited due to the absence of structures of an intact human muscle AChR. Here, we overcome challenges in receptor purification and present high-resolution cryo-EM structures of the human adult AChR in different functional states. Using a panel of six MG patient-derived monoclonal antibodies, we mapped distinct epitopes involved in diverse pathogenic mechanisms, including receptor blockade, internalization, and complement activation. Electrophysiological and binding assays further defined how these autoantibodies impair AChR function. These findings provide critical insights into MG immunopathology, revealing previously unrecognized antibody epitope diversity and mechanisms of receptor inhibition, offering a foundation for personalized therapies targeting antibody-mediated autoimmune disorders. HighlightsO_LIHuman adult muscle AChR receptor structures in resting and desensitized states C_LIO_LIEpitope mapping for mechanistically distinct pathogenic MG autoantibodies C_LIO_LIStructural and functional elucidation of different inhibition mechanisms in MG C_LI

neuroscience↗

bioRxiv2020

Self-antigen driven affinity maturation is required for pathogenic monovalent IgG4 autoantibody development

Pathogenic IgG4 autoantibodies in autoimmune myasthenia gravis (MG) are functionally monovalent as a result of Fab-arm exchange. The origin and development of these unique autoantibodies are not well understood. We examined MG patient-derived monoclonal autoantibodies (mAbs), their corresponding germline-encoded unmutated common ancestors (UCA) and monovalent antigen-binding fragments (Fabs) to investigate how antigen-driven affinity maturation contributes to both binding and immunopathology. Mature mAbs, their UCA counterparts and mature monovalent Fabs bound to the autoantigen and retained their pathogenic capacity. However, monovalent UCA Fabs still bound the autoantigen but lost their pathogenic capacity. The mature Fabs were characterized by very high affinity (sub-nanomolar) driven by a rapid on-rate and slow off-rate. However, the UCA affinity was approximately 100-fold less than that of the mature Fabs, which was driven by a rapid off-rate. Crystal structures of two Fabs shed light on how mutations acquired during affinity maturation may contribute to increased MuSK binding affinity. These collective findings indicate that the autoantigen initiates the autoimmune response in MuSK MG and drives autoimmunity through the accumulation of somatic hypermutation such that monovalent IgG4 Fab-arm exchanged MG autoantibodies reach a high affinity threshold required for pathogenic capacity. SummaryIgG4 autoantibodies in autoimmune myasthenia gravis are functionally monovalent, requiring a high affinity threshold featuring fast on/slow off rates, to reach pathogenic capacity. This capacity is dependent on self-antigen initiated and driven maturation, which includes the accumulation of indispensable somatic hypermutations that may alter electrostatic interactions with the antigen.

immunology↗

bioRxiv2018

Isolation and characterization of rare circulating autoantibody-producing cells from patients with muscle-specific kinase myasthenia gravis

Myasthenia gravis (MG) is a chronic autoimmune disorder characterized by muscle weakness and caused by autoantibodies that bind to functional membrane proteins at the neuromuscular junction. Most patients have autoantibodies to the acetylcholine receptor (AChR), but a subset of patients instead have autoantibodies to muscle specific tyrosine kinase (MuSK). MuSK is an essential component of the Agrin/Lipoprotein receptor-related protein 4(LRP4)/MuSK/downstream of tyrosine kinase 7 (DOK7) pathway that is responsible for synaptic differentiation, including clustering of AChRs at the neuromuscular junction, both during development and in adult muscle. Nerve-released Agrin binds to LRP4 which then binds to MuSK, stimulating autophosphorylation and recruitment of DOK7 to complete the membrane component of the pathway. Serum-derived IgG4 subclass MuSK autoantibodies prevent the binding of LRP4 to MuSK, subsequently impairing autophosphorylation, resulting in the loss of Agrin-induced AChR clustering in the mouse myotube-forming C2C12 line. Although this autoimmune mechanism appears well understood, MuSK autoantibodies from patients are polyclonal. Most are IgG4 but IgG1, 2 and 3 are also present and can achieve similar results on AChR clustering. In addition, most bind the first Ig-like domain in MuSK, however some patients harbor serum autoantibodies that recognize other domains in MuSK. We sought to establish individual MuSK IgG clones so that the disease mechanisms could be better understood. We isolated MuSK autoantibody-expressing B cells from MuSK MG patients with a fluorescent-tagged MuSK antigen multimer and generated a panel of human monoclonal autoantibodies (mAbs) from these cells. We produced 77 mAbs from single B cells collected from six MuSK MG patients. Here we focused on three highly specific mAbs that bound quantitatively to MuSK in solution, to MuSK-expressing HEK cells and at mouse neuromuscular junctions where they co-localized with AChRs. These three IgG isotype mAbs (two IgG4 and one IgG3 subclass) recognized the Ig-like domain 2 of MuSK. The three MuSK mAbs inhibited Agrin induced-AChR clustering in C2C12 myotubes, but intriguingly, they enhanced rather than inhibited MuSK phosphorylation. This approach for ex vivo isolation of MuSK MG autoantibody-producing cells and production of human recombinant mAbs has identified distinct autoantibody specificities and likely divergent effector mechanisms. Collectively, these findings will enable a better understanding of MuSK autoantibody-mediated pathology.

immunology↗

bioRxiv2018

Identification of subject-specific immunoglobulin alleles from expressed repertoire sequencing data

The adaptive immune receptor repertoire (AIRR) contains information on an individuals immune past, present and potential in the form of the evolving sequences that encode the B cell receptor (BCR) repertoire. AIRR sequencing (AIRR-seq) studies rely on databases of known BCR germline variable (V), diversity (D) and joining (J) genes to detect somatic mutations in AIRR-seq data via comparison to the best-aligning database alleles. However, it has been shown that these databases are far from complete, leading to systematic misidentification of mutated positions in subsets of sample sequences. We previously presented TIgGER, a computational method to identify subject-specific V gene genotypes, including the presence of novel V gene alleles, directly from AIRR-seq data. However, the original algorithm was unable to detect alleles that differed by more than 5 single nucleotide polymorphisms (SNPs) from a database allele. Here we present and apply an improved version of the TIgGER algorithm which can detect alleles that differ by any number of SNPs from the nearest database allele, and can construct subject-specific genotypes with minimal prior information. TIgGER predictions are validated both computationally (using a leave-one-out strategy) and experimentally (using genomic sequencing), resulting in the addition of three new immunoglobulin heavy chain V (IGHV) gene alleles to the IMGT repertoire. Finally, we develop a Bayesian strategy to provide a confidence estimate associated with genotype calls. All together, these methods allow for much higher accuracy in germline allele assignment, an essential step in AIRR-seq studies.

bioinformatics↗