RESUMEN
Mechanisms of B cell tolerance act during development in the bone marrow and periphery to eliminate or restrict autoreactive clones to prevent autoimmune disease. B cells in the spleens of mice that harbor anti-insulin BCR transgenes (125Tg) are maintained in a functionally silenced or anergic state by endogenous hormone, but it is not clear when and where anergy is induced. An in vitro bone marrow culture system was therefore used to probe whether small protein hormones, a critical class of autoantigens, could interact with the BCR to induce anergy early during B cell development. Upon exposure to insulin, anti-insulin (125Tg) immature B cells show similar hallmarks of anergy as those observed in mature splenic B cells. These include BCR down-regulation, impaired proliferative responses to anti-CD40, and diminished calcium mobilization upon stimulation with BCR-dependent and independent stimuli. Inhibition of calcineurin also results in reduced immature B cell proliferation in a similar manner, suggesting a potential mechanism through which reduced intracellular calcium mobilization may be altering cellular proliferation. Signs of impairment appear after short-term exposure to insulin, which are reversible upon Ag withdrawal. This suggests that a high degree of functional plasticity is maintained at this stage and that constant Ag engagement is required to maintain functional inactivation. These findings indicate that tolerance observed in mature, splenic 125Tg B cells is initiated by insulin in the developing B cell compartment and thus highlight an important therapeutic window for the prevention of insulin autoimmunity.
Asunto(s)
Anergia Clonal/genética , Silenciador del Gen , Anticuerpos Insulínicos/fisiología , Insulina/inmunología , Células Precursoras de Linfocitos B/inmunología , Células Precursoras de Linfocitos B/metabolismo , Animales , Células de la Médula Ósea/citología , Células de la Médula Ósea/inmunología , Células de la Médula Ósea/metabolismo , Antígenos CD40/inmunología , Antígenos CD40/metabolismo , Señalización del Calcio/inmunología , Diferenciación Celular/inmunología , Línea Celular Tumoral , Proliferación Celular , Células Cultivadas , Insulina/metabolismo , Anticuerpos Insulínicos/biosíntesis , Interleucina-7/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Células Precursoras de Linfocitos B/citologíaRESUMEN
B lymphocytes that recognize soluble self-Ags are routinely found in normal individuals in a functionally inactive or anergic state. Current models indicate that this tolerant state is maintained by interactions with self-Ags that uncouple the BCR from downstream signaling pathways and increase levels of free calcium. Contrary to this expectation, B cells that harbor anti-insulin Ig transgenes (125Tg) are maintained in a tolerant state even though free calcium levels remain normal and tyrosine kinase substrate phosphorylation is preserved following BCR stimulation. Under basal conditions, intracellular levels of inositol 1,4,5-trisphosphate are increased and NFATc1 levels are reduced in 125Tg B cells. The 125Tg B cells are markedly impaired in their ability to mobilize calcium upon stimulation with ionomycin, and BCR-induced calcium mobilization from internal stores is decreased. In contrast, poisoning intracellular calcium pumps with thapsigargin increases calcium mobilization in 125Tg B cells. Changes in calcium signaling are accompanied by a failure of 125Tg B cells to translocate NFATc1 into the nucleus following stimulation with either anti-IgM or ionomycin. Thus, disassociation of BCR from multiple signaling pathways is not essential for maintaining tolerance in anti-insulin 125Tg B cells. Rather, BCRs that are occupied by autologous insulin deliver signals that induce changes in intracellular calcium mobilization and maintain tolerance by preventing activation of key transcription factors such as NFAT.
Asunto(s)
Subgrupos de Linfocitos B/inmunología , Señalización del Calcio/inmunología , Calcio/metabolismo , Tolerancia Inmunológica , Insulina/inmunología , Factores de Transcripción NFATC/metabolismo , Animales , Subgrupos de Linfocitos B/metabolismo , Calcio/antagonistas & inhibidores , Señalización del Calcio/genética , Células Cultivadas , Tolerancia Inmunológica/genética , Inmunoglobulina M/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Factores de Transcripción NFATC/antagonistas & inhibidoresRESUMEN
Loss of tolerance is considered to be an early event that is essential for the development of autoimmune disease. In contrast to this expectation, autoimmune (type 1) diabetes develops in NOD mice that harbor an anti-insulin Ig transgene (125Tg), even though anti-insulin B cells are tolerant. Tolerance is maintained in a similar manner in both normal C57BL/6 and autoimmune NOD mice, as evidenced by B cell anergy to stimulation through their Ag receptor (anti-IgM), TLR4 (LPS), and CD40 (anti-CD40). Unlike B cells in other models of tolerance, anergic 125Tg B cells are not arrested in development, and they enter mature subsets of follicular and marginal zone B cells. In addition, 125Tg B cells remain competent to increase CD86 expression in response to both T cell-dependent (anti-CD40) and T cell-independent (anti-IgM or LPS) signals. Thus, for anti-insulin B cells, tolerance is characterized by defective B cell proliferation uncoupled from signals that promote maturation and costimulator function. In diabetes-prone NOD mice, anti-insulin B cells in this novel state of tolerance provide the essential B cell contribution required for autoimmune beta cell destruction. These findings suggest that the degree of functional impairment, rather than an overt breach of tolerance, is a critical feature that governs B cell contribution to T cell-mediated autoimmune disease.