RESUMO
Protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene polymorphisms are associated with many autoimmune diseases. The major risk allele encodes an R620W amino acid change that alters B cell receptor (BCR) signaling involved in the regulation of central B cell tolerance. To assess whether this PTPN22 risk allele affects the removal of developing autoreactive B cells, we tested by ELISA the reactivity of recombinant antibodies isolated from single B cells from asymptomatic healthy individuals carrying one or two PTPN22 risk allele(s) encoding the PTPN22 R620W variant. We found that new emigrant/transitional and mature naive B cells from carriers of this PTPN22 risk allele contained high frequencies of autoreactive clones compared with those from non-carriers, revealing defective central and peripheral B cell tolerance checkpoints. Hence, a single PTPN22 risk allele has a dominant effect on altering autoreactive B cell counterselection before any onset of autoimmunity. In addition, gene array experiments analyzing mature naive B cells displaying PTPN22 risk allele(s) revealed that the association strength of PTPN22 for autoimmunity may be due not only to the impaired removal of autoreactive B cells but also to the upregulation of genes such as CD40, TRAF1, and IRF5, which encode proteins that promote B cell activation and have been identified as susceptibility genes associated with autoimmune diseases. These data demonstrate that early B cell tolerance defects in autoimmunity can result from specific polymorphisms and precede the onset of disease.
Assuntos
Alelos , Autoimunidade/imunologia , Linfócitos B/imunologia , Isoenzimas/genética , Proteína Tirosina Fosfatase não Receptora Tipo 22/genética , Autoanticorpos/imunologia , Doenças Autoimunes/genética , Doenças Autoimunes/imunologia , Linfócitos B/citologia , Predisposição Genética para Doença , Humanos , Isoenzimas/metabolismo , Polimorfismo de Nucleotídeo Único , Proteína Tirosina Fosfatase não Receptora Tipo 22/metabolismo , Fatores de Risco , Tolerância a Antígenos Próprios/genética , Tolerância a Antígenos Próprios/imunologiaRESUMO
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. In addition, B-cell tolerance was further breached in AID-deficient patients as illustrated by the detection of anti-nuclear IgM antibodies in the serum of all patients. Thus, we identified a major and previously unsuspected role for AID in the removal of developing autoreactive B cells in humans.
Assuntos
Linfócitos B/enzimologia , Linfócitos B/imunologia , Citidina Desaminase/imunologia , Tolerância a Antígenos Próprios/imunologia , Adolescente , Adulto , Sequência de Aminoácidos , Anticorpos Antinucleares/sangue , Anticorpos Antinucleares/genética , Fator Ativador de Células B/sangue , Estudos de Casos e Controles , Criança , Pré-Escolar , Citidina Desaminase/deficiência , Citidina Desaminase/genética , Feminino , Humanos , Imunoglobulina M/sangue , Imunoglobulina M/genética , Síndrome de Job/enzimologia , Síndrome de Job/genética , Síndrome de Job/imunologia , Masculino , Pessoa de Meia-Idade , Dados de Sequência Molecular , Mutação , Células Precursoras de Linfócitos B/enzimologia , Células Precursoras de Linfócitos B/imunologia , Tolerância a Antígenos Próprios/genética , Linfócitos T Reguladores/enzimologia , Linfócitos T Reguladores/imunologia , Adulto JovemRESUMO
Complement receptor 2-negative (CR2/CD21(-)) B cells have been found enriched in patients with autoimmune diseases and in common variable immunodeficiency (CVID) patients who are prone to autoimmunity. However, the physiology of CD21(-/lo) B cells remains poorly characterized. We found that some rheumatoid arthritis (RA) patients also display an increased frequency of CD21(-/lo) B cells in their blood. A majority of CD21(-/lo) B cells from RA and CVID patients expressed germline autoreactive antibodies, which recognized nuclear and cytoplasmic structures. In addition, these B cells were unable to induce calcium flux, become activated, or proliferate in response to B-cell receptor and/or CD40 triggering, suggesting that these autoreactive B cells may be anergic. Moreover, gene array analyses of CD21(-/lo) B cells revealed molecules specifically expressed in these B cells and that are likely to induce their unresponsive stage. Thus, CD21(-/lo) B cells contain mostly autoreactive unresponsive clones, which express a specific set of molecules that may represent new biomarkers to identify anergic B cells in humans.
