Autoreactivity in naïve human fetal B cells is associated with commensal bacteria recognition.

Restricted V(D)J recombination during fetal development was postulated to limit antibody repertoire breadth and prevent autoimmunity. However, newborn serum contains abundant autoantibodies, suggesting that B cell tolerance during gestation is not yet fully established. To investigate this apparent paradox, we evaluated the reactivities of more than 450 antibodies cloned from single B cells from human fetal liver, bone marrow, and spleen.

Accumulation of Antigen-Driven Lymphoproliferations in Complement Receptor 2/CD21 B Cells From Patients With Sjögren's Syndrome.

Objective: Patients with Sjögren's syndrome (SS) are prone to develop malignant lymphomas, and a correlation has been established between the lymphoproliferations occurring in these disorders and the presence in patients' blood of an unusual B cell population that down-regulates complement receptor 2/CD21. This study was undertaken to identify the B cell compartment from which these lymphoproliferations emerge and determine the mechanisms that promote clonal B cell expansion in patients with SS.

Methods: The reactivity of antibodies expressed by CD19+CD10-CD27-IgM+CD21 cells isolated from the blood of patients with SS was tested using a polymerase chain reaction-based approach that allows us to clone and express, in vitro, recombinant antibodies produced by single B cells.

Defective Early B Cell Tolerance Checkpoints in Sjögren's Syndrome Patients.

Objective: Central and peripheral B cell tolerance checkpoints are defective in many patients with autoimmune diseases, but the functionality of each discrete checkpoint has not been assessed in patients with Sjögren's syndrome (SS). We undertook this study to assess this functionality in SS patients.

Methods: Using a polymerase chain reaction-based approach that allows us to clone and express, in vitro, recombinant antibodies produced by single B cells, we tested the reactivity of recombinant antibodies cloned from single CD19+CD21 CD10+IgM CD27- newly emigrant/transitional B cells and CD19+CD21+CD10-IgM+CD27- mature naive B cells from 5 SS patients.

PTPN22 inhibition resets defective human central B cell tolerance.

The () allele is one of the main risk factors associated with many autoimmune diseases and correlates with a defective removal of developing autoreactive B cells in humans. To determine whether inhibiting PTPN22 favors the elimination of autoreactive B cells, we first demonstrated that the allele interfered with the establishment of central B cell tolerance using NOD-scid-common γ chain knockout (NSG) mice engrafted with human hematopoietic stem cells expressing this allele. In contrast, the inhibition of either PTPN22 enzymatic activity or its expression by RNA interference restored defective central B cell tolerance in this model.

Decreased somatic hypermutation induces an impaired peripheral B cell tolerance checkpoint.

Patients with mutations in AICDA, which encodes activation-induced cytidine deaminase (AID), display an impaired peripheral B cell tolerance. AID mediates class-switch recombination (CSR) and somatic hypermutation (SHM) in B cells, but the mechanism by which AID prevents the accumulation of autoreactive B cells in blood is unclear. Here, we analyzed B cell tolerance in AID-deficient patients, patients with autosomal dominant AID mutations (AD-AID), asymptomatic AICDA heterozygotes (AID+/-), and patients with uracil N-glycosylase (UNG) deficiency, which impairs CSR but not SHM.

Compromised fidelity of B-cell tolerance checkpoints in AChR and MuSK myasthenia gravis.

Objective: Myasthenia gravis (MG) is an autoimmune condition in which neurotransmission is impaired by binding of autoantibodies to acetylcholine receptors (AChR) or, in a minority of patients, to muscle specific kinase (MuSK). There are differences in the dominant IgG subclass, pathogenic mechanisms, and treatment responses between the two MG subtypes (AChR or MuSK). The antibodies are thought to be T-cell dependent, but the mechanisms underlying their production are not well understood.

Maturational characteristics of HIV-specific antibodies in viremic individuals.

Despite the rare appearance of potent HIV-neutralizing mAbs in infected individuals requiring prolonged affinity maturation, little is known regarding this process in the majority of viremic individuals. HIV-infected individuals with chronic HIV viremia have elevated numbers of nonconventional tissue-like memory (TLM) B cells that predominate in blood over conventional resting memory (RM) B cells. Accordingly, we investigated affinity maturation in these 2 memory B cell populations.

Activation-Induced Cytidine Deaminase Expression in Human B Cell Precursors Is Essential for Central B Cell Tolerance.

Activation-induced cytidine deaminase (AID), the enzyme-mediating class-switch recombination (CSR) and somatic hypermutation (SHM) of immunoglobulin genes, is essential for the removal of developing autoreactive B cells. How AID mediates central B cell tolerance remains unknown. We report that AID enzymes were produced in a discrete population of immature B cells that expressed recombination-activating gene 2 (RAG2), suggesting that they undergo secondary recombination to edit autoreactive antibodies.

Salmonella Infection Drives Promiscuous B Cell Activation Followed by Extrafollicular Affinity Maturation.

The B cell response to Salmonella typhimurium (STm) occurs massively at extrafollicular sites, without notable germinal centers (GCs). Little is known in terms of its specificity. To expand the knowledge of antigen targets, we screened plasmablast (PB)-derived monoclonal antibodies (mAbs) for Salmonella specificity, using ELISA, flow cytometry, and antigen microarray.

Dedicator of cytokinesis 8-deficient patients have a breakdown in peripheral B-cell tolerance and defective regulatory T cells.

Background: Dedicator of cytokinesis 8 (DOCK8) deficiency is typified by recurrent infections, increased serum IgE levels, eosinophilia, and a high incidence of allergic and autoimmune manifestations.

Objective: We sought to determine the role of DOCK8 in the establishment and maintenance of human B-cell tolerance.

Methods: Autoantibodies were measured in the plasma of DOCK8-deficient patients.

Activation-induced cytidine deaminase (AID) is required for B-cell tolerance in humans.

Impaired immune functions leading to primary immunodeficiencies often correlate with paradoxical autoimmune complications; patients with hyper-IgM syndromes who are deficient in activation-induced cytidine deaminase (AID), which is required for class-switch recombination and somatic hypermutation, are prone to develop autoimmune diseases. To investigate the impact of AID-deficiency on early B-cell tolerance checkpoints in humans, we tested by ELISA the reactivity of recombinant antibodies isolated from single B cells from AID-deficient patients. New emigrant/transitional and mature naive B cells from AID-deficient patients express an abnormal Ig repertoire and high frequencies of autoreactive antibodies, demonstrating that AID is required for the establishment of both central and peripheral B-cell tolerance.