RESUMEN
Using an 'oligoclonal' model, we have previously shown that mice transgenic for a mu chain (H3) and deficient for kappa chain expression display a mature B cell repertoire largely dominated by the H3/lambda1 pair, while the four H3/lambda available combinations can be observed in the immature B cell compartment. This led us to propose the existence of a positive selection process. To test this hypothesis, we have introduced the SJL lambda locus coding for a defective lambda1 chain (lambda1(s)) that creates a dysfunctional Ig receptor complex during B cell differentiation. Our results show that the lambda1(s) defect impairs the development of mature B cells when the H3-mu transgene insert is present in the hemizygous state. This suggests that the Gly --> Val substitution present in the C(lambda)1(s) chain at position 155 is sufficient to abrogate the selection of the H3/lambda1 pair. Unexpectedly, when the H3-mu transgene array is present in a homozygous state in lambda1(s) mice but not in 'wild-type' lambda1 mice (lambda1(+)), a significant number of mature B cells expressing all H3/lambda combinations can be developed. These results indicate that the overriding H3/lambda1 dominance observed in lambda1(+) mice is due to a positive selection process and not to a negative selection of other H3/lambda combinations. They also show that the export of B cells to the periphery can be controlled by the expression of the mu chain.
Asunto(s)
Subgrupos de Linfocitos B/inmunología , Supresión Clonal/fisiología , Genes de Inmunoglobulinas , Cadenas kappa de Inmunoglobulina/genética , Cadenas lambda de Inmunoglobulina/genética , Cadenas mu de Inmunoglobulina/genética , Sustitución de Aminoácidos , Animales , Diferenciación Celular , Cadenas lambda de Inmunoglobulina/biosíntesis , Cadenas mu de Inmunoglobulina/biosíntesis , Recuento de Linfocitos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Fenotipo , Mutación Puntual , TransgenesRESUMEN
The genes coding for TCR alpha and delta chains share the same genetic locus (TCRA/D). The rules governing the utilization of a V gene with the alpha and delta chains have not been established. More specifically, it is not known whether the position of a gene within the locus influences its utilization in alpha and delta TCR. To elucidate these points, we mapped ADV2 genes in the TCRA/D locus of BALB/c mice and analyzed their utilization in TCR alpha and delta transcripts from thymi isolated from mice of different ages. Our results show that all ADV2 genes can be used by the two chains, but with strikingly different patterns. Moreover, ADV2 utilization by the alpha chain proceeds in successive concentric waves during development, suggesting a progressive regulation of gene accessibility and utilization. These results support independent control of TCRA and TCRD gene assembly.
Asunto(s)
Reordenamiento Génico de la Cadena alfa de los Receptores de Antígenos de los Linfocitos T , Reordenamiento Génico de la Cadena delta de los Receptores de Antígenos de los Linfocitos T , Genes Codificadores de la Cadena alfa de los Receptores de Linfocito T/genética , Genes Codificadores de la Cadena delta de los Receptores de Linfocito T/genética , Animales , Southern Blotting , Mapeo Cromosómico , Clonación Molecular , Regulación del Desarrollo de la Expresión Génica , Ratones , Ratones Endogámicos BALB C , ARN Mensajero/genética , Transcripción GenéticaRESUMEN
To know whether each newly formed B cell has an equal chance of survival in the organism, we analyzed the composition of the B cell repertoire of extremely limited diversity by generating mu-transgenic kappa-knockout mice. Surprisingly, in both types of mice studied, the B cell repertoire is mainly composed of cells expressing the mu-transgene-encoded chain associated with only one out four available lambda types depending on the mu transgene. Moreover, B cell differentiation cultures in vitro show that newly formed B cells can express the various lambda types regardless of the presence or absence of the mu transgenes. These results show a drastic impact of the heavy chain on the lambda light chain repertoire expressed in the periphery. The overexpression of a unique heavy/light chain pairing therefore results from selective processes. The immature B cells may be positively selected to provide the immunocompetent B cells in the periphery.
Asunto(s)
Subgrupos de Linfocitos B/inmunología , Subgrupos de Linfocitos B/metabolismo , Animales , Subgrupos de Linfocitos B/citología , Supervivencia Celular/genética , Supervivencia Celular/inmunología , Células Cultivadas , Reordenamiento Génico de Cadena Ligera de Linfocito B , Cadenas lambda de Inmunoglobulina/genética , Cadenas mu de Inmunoglobulina/genética , Lipopolisacáridos/inmunología , Activación de Linfocitos/genética , Ratones , Ratones Noqueados , Ratones Transgénicos , Salmonella typhimurium/inmunología , Transgenes/inmunologíaRESUMEN
Analysis of the B cell repertoire is complicated by the huge diversity inherent in the germ line determined combinatory. Making use of knockout technology, kappa-deficient mice have been obtained. They constitute a shrewd model to follow the expression of an Ig minilocus, such as the lambda one, in the normal condition compared with classical transgenic models. Indeed, in contrast to wild type mice, in which only 5% of lambda B cells are produced, these mutant mice exclusively produce lambda positive B cells. Although, the lambda locus is well characterized and has a relatively simple organization, the mechanistic and selective pressures that govern its utilization are still poorly understood. The analysis of the lambda B cell repertoire in kappa-deficient mice, should therefore bring more conclusive informations. Here we present the lambda subtype distribution in the various cellular compartments of the kappa-deficient mice, and discuss the rules that can be responsible for this distribution. Our recent data indicate that the lambda subtype proportions in the bone marrow and the spleen result, for the major part, from mechanistic processes (i.e., recombinase accessibility, production of V-J functional joint and H/L pairings) while the lambda proportions found in the peritoneal cavity ensue from selective processes. Finally, the capacity to respond to various antigens is discussed from such a generated lambda B cell repertoire.