RESUMEN
Monoallelic AgR gene expression underlies specific adaptive immune responses. AgR allelic exclusion is achieved by sequential initiation of V(D)J recombination between alleles and resultant protein from one allele signaling to prevent recombination of the other. The ATM kinase, a regulator of the DNA double-strand break (DSB) response, helps enforce allelic exclusion through undetermined mechanisms. ATM promotes repair of RAG1/RAG2 (RAG) endonuclease-induced DSBs and transduces signals from RAG DSBs during Igk gene rearrangement on one allele to transiently inhibit RAG1 protein expression, Igk accessibility, and RAG cleavage of the other allele. Yet, the relative contributions of ATM functions in DSB repair versus signaling to enforce AgR allelic exclusion remain undetermined. In this study, we demonstrate that inactivation in mouse pre-B cells of the NF-κB essential modulator (Nemo) protein, an effector of ATM signaling, diminishes RAG DSB-triggered repression of Rag1/Rag2 transcription and Igk accessibility but does not result in aberrant repair of RAG DSBs like ATM inactivation. We show that Nemo deficiency increases simultaneous biallelic Igk cleavage in pre-B cells and raises the frequency of B cells expressing Igκ proteins from both alleles. In contrast, the incidence of biallelic Igκ expression is not elevated by inactivation of the SpiC transcriptional repressor, which is induced by RAG DSBs in an ATM-dependent manner and suppresses Igk accessibility. Thus, we conclude that Nemo-dependent, ATM-mediated DNA damage signals enforce Igκ allelic exclusion by orchestrating transient repression of RAG expression and feedback inhibition of additional Igk rearrangements in response to RAG cleavage on one Igk allele.
Asunto(s)
Roturas del ADN de Doble Cadena , Reparación del ADN/genética , Inmunoglobulinas/inmunología , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Pérdida de Heterocigocidad/genética , Animales , Proteínas de la Ataxia Telangiectasia Mutada/genética , Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Células Cultivadas , Anergia Clonal/genética , Anergia Clonal/inmunología , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Región Variable de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/inmunología , Inmunoglobulinas/genética , Péptidos y Proteínas de Señalización Intracelular/genética , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Recombinación V(D)J/genéticaRESUMEN
Tuberculosis was a major cause of population decline among Brazilian indigenous peoples and remains a leading cause of morbidity and mortality among them. Despite high BCG coverage, results of Tuberculin Skin Test (TST) reactivity have shown high rates of anergy in Amazonian Indians. Given the high prevalence of anergy in these populations and the fact that genetic host factors play an important role in susceptibility to Mycobacterium tuberculosis (MTB), the aim of this study was to evaluate the association of nineteen polymorphisms in fifteen genes related to immune response and anergy in the Xavante, an indigenous group from Brazil. A total of 481 individuals were investigated. TST anergy was observed in 69% of them. Polymorphisms in four genes showed absence or very low variability: SP110, PTPN22, IL12RB1 and IL6. IFNG +874 A/T heterozygotes and IL4-590 C/C homozygotes were more frequent in those individuals who presented a positive TST (prevalence ratios of 1.9 and 2.0 respectively). The risk of anergy was 1.5 in IL10-1082 G/G homozygotes when compared to carriers for the A allele. In indigenous groups such as the Xavante exposure to a variety of infections, associated with specific genetic factors, may disturb the T-helper 1 and T-helper 2 balance leading to increased immunological susceptibility.