RESUMEN
The processes leading from disturbed B-cell development to adult B-cell progenitor acute lymphoblastic leukemia (BCP-ALL) remain poorly understood. Here, we describe Irf4-/- mice as prone to developing BCP-ALL with age. Irf4-/- preB-I cells exhibited impaired differentiation but enhanced proliferation in response to IL-7, along with reduced retention in the IL-7 providing bone marrow niche due to decreased CXCL12 responsiveness. Thus selected, preB-I cells acquired Jak3 mutations, probably following irregular AID activity, resulting in malignant transformation. We demonstrate heightened IL-7 sensitivity due to Jak3 mutants, devise a model to explain it, and describe structural and functional similarities to Jak2 mutations often occurring in human Ph-like ALL. Finally, targeting JAK signaling with Ruxolitinib in vivo prolonged survival of mice bearing established Irf4-/- leukemia. Intriguingly, organ infiltration including leukemic meningeosis was selectively reduced without affecting blood blast counts. In this work, we present spontaneous leukemogenesis following IRF4 deficiency with potential implications for high-risk BCP-ALL in adult humans.
Asunto(s)
Linfoma de Burkitt , Leucemia-Linfoma Linfoblástico de Células Precursoras , Adulto , Animales , Humanos , Ratones , Linfocitos B , Linfoma de Burkitt/patología , Interleucina-7/genética , Janus Quinasa 3/genética , Mutación/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras/genética , Transducción de SeñalRESUMEN
Effective vaccines and monoclonal antibodies have been developed against coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, the appearance of virus variants with higher transmissibility and pathogenicity is a major concern because of their potential to escape vaccines and clinically approved SARS-CoV-2- antibodies. Here, we use flow cytometry-based binding and pseudotyped SARS-CoV-2 neutralization assays to determine the efficacy of boost immunization and therapeutic antibodies to neutralize the dominant Omicron variant. We provide compelling evidence that the third vaccination with BNT162b2 increases the amount of neutralizing serum antibodies against Delta and Omicron variants, albeit to a lower degree when compared to the parental Wuhan strain. Therefore, a third vaccination is warranted to increase titers of protective serum antibodies, especially in the case of the Omicron variant. We also found that most clinically approved and otherwise potent therapeutic antibodies against the Delta variant failed to recognize and neutralize the Omicron variant. In contrast, some antibodies under preclinical development potentially neutralized the Omicron variant. Our studies also support using a flow cytometry-based antibody binding assay to rapidly monitor therapeutic candidates and serum titers against emerging SARS-CoV-2 variants.
Asunto(s)
Antineoplásicos Inmunológicos , COVID-19 , Anticuerpos Monoclonales , Anticuerpos Neutralizantes , Anticuerpos Antivirales , Vacuna BNT162 , Vacunas contra la COVID-19 , Humanos , SARS-CoV-2 , VacunaciónRESUMEN
We have previously shown that the microRNA (miRNA) processor complex consisting of the RNAse Drosha and the DiGeorge Critical Region (DGCR) 8 protein is essential for B cell maturation. To determine whether miRNA processing is required to initiate T cell-mediated antibody responses, we deleted DGCR8 in maturing B2 cells by crossing a mouse with loxP-flanked DGCR8 alleles with a CD23-Cre mouse. As expected, non-immunized mice showed reduced numbers of mature B2 cells and IgG-secreting cells and diminished serum IgG titers. In accordance, germinal centers and antigen-specific IgG-secreting cells were absent in mice immunized with T-dependent antigens. Therefore, DGCR8 is required to mount an efficient T-dependent antibody response. However, DGCR8 deletion in B1 cells was incomplete, resulting in unaltered B1 cell numbers and normal IgM and IgA titers in DGCR8-knock-out mice. Therefore, this mouse model could be used to analyze B1 responses in the absence of functional B2 cells.
Asunto(s)
MicroARNs , Ratones , Animales , MicroARNs/genética , MicroARNs/metabolismo , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Linfocitos T/metabolismo , Centro Germinal/metabolismo , Inmunoglobulina G/metabolismoRESUMEN
TRIANNI mice carry an entire set of human immunoglobulin V region gene segments and are a powerful tool to rapidly isolate human monoclonal antibodies. After immunizing these mice with DNA encoding the spike protein of SARS-CoV-2 and boosting with spike protein, we identified 29 hybridoma antibodies that reacted with the SARS-CoV-2 spike protein. Nine antibodies neutralize SARS-CoV-2 infection at IC50 values in the subnanomolar range. ELISA-binding studies and DNA sequence analyses revealed one cluster of three clonally related neutralizing antibodies that target the receptor-binding domain and compete with the cellular receptor hACE2. A second cluster of six clonally related neutralizing antibodies bind to the N-terminal domain of the spike protein without competing with the binding of hACE2 or cluster 1 antibodies. SARS-CoV-2 mutants selected for resistance to an antibody from one cluster are still neutralized by an antibody from the other cluster. Antibodies from both clusters markedly reduced viral spread in mice transgenic for human ACE2 and protected the animals from SARS-CoV-2-induced weight loss. The two clusters of potent noncompeting SARS-CoV-2 neutralizing antibodies provide potential candidates for therapy and prophylaxis of COVID-19. The study further supports transgenic animals with a human immunoglobulin gene repertoire as a powerful platform in pandemic preparedness initiatives.
Asunto(s)
COVID-19 , Glicoproteína de la Espiga del Coronavirus , Animales , Anticuerpos Monoclonales , Anticuerpos Neutralizantes , Anticuerpos Antivirales , Humanos , Ratones , SARS-CoV-2RESUMEN
The systemic processes involved in the manifestation of life-threatening COVID-19 and in disease recovery are still incompletely understood, despite investigations focusing on the dysregulation of immune responses after SARS-CoV-2 infection. To define hallmarks of severe COVID-19 in acute disease (n = 58) and in disease recovery in convalescent patients (n = 28) from Hannover Medical School, we used flow cytometry and proteomics data with unsupervised clustering analyses. In our observational study, we combined analyses of immune cells and cytokine/chemokine networks with endothelial activation and injury. ICU patients displayed an altered immune signature with prolonged lymphopenia but the expansion of granulocytes and plasmablasts along with activated and terminally differentiated T and NK cells and high levels of SARS-CoV-2-specific antibodies. The core signature of seven plasma proteins revealed a highly inflammatory microenvironment in addition to endothelial injury in severe COVID-19. Changes within this signature were associated with either disease progression or recovery. In summary, our data suggest that besides a strong inflammatory response, severe COVID-19 is driven by endothelial activation and barrier disruption, whereby recovery depends on the regeneration of the endothelial integrity.
Asunto(s)
Anticuerpos Antivirales/sangre , Proteínas Sanguíneas/metabolismo , COVID-19/diagnóstico , Síndrome de Liberación de Citoquinas/diagnóstico , Endotelio Vascular/virología , Linfopenia/diagnóstico , SARS-CoV-2/patogenicidad , Biomarcadores/sangre , Proteína C-Reactiva/metabolismo , COVID-19/inmunología , COVID-19/mortalidad , COVID-19/virología , Quimiocina CXCL10/sangre , Quimiocina CXCL9/sangre , Análisis por Conglomerados , Convalecencia , Síndrome de Liberación de Citoquinas/inmunología , Síndrome de Liberación de Citoquinas/mortalidad , Síndrome de Liberación de Citoquinas/virología , Progresión de la Enfermedad , Endotelio Vascular/inmunología , Granulocitos/inmunología , Granulocitos/virología , Factores de Crecimiento de Célula Hematopoyética/sangre , Factor de Crecimiento de Hepatocito/sangre , Humanos , Unidades de Cuidados Intensivos , Subunidad p40 de la Interleucina-12/sangre , Interleucina-6/sangre , Interleucina-8/sangre , Células Asesinas Naturales/inmunología , Células Asesinas Naturales/virología , Lectinas Tipo C/sangre , Linfopenia/inmunología , Linfopenia/mortalidad , Linfopenia/virología , Células Plasmáticas/inmunología , Células Plasmáticas/virología , Análisis de Supervivencia , Linfocitos T/inmunología , Linfocitos T/virologíaRESUMEN
Viral mutations are an emerging concern in reducing SARS-CoV-2 vaccination efficacy. Second-generation vaccines will need to elicit neutralizing antibodies against sites that are evolutionarily conserved across the sarbecovirus subgenus. Here, we immunized mice containing a human antibody repertoire with diverse sarbecovirus receptor-binding domains (RBDs) to identify antibodies targeting conserved sites of vulnerability. Antibodies with broad reactivity against diverse clade B RBDs targeting the conserved class 4 epitope, with recurring IGHV/IGKV pairs, were readily elicited but were non-neutralizing. However, rare class 4 antibodies binding this conserved RBD supersite showed potent neutralization of SARS-CoV-2 and all variants of concern. Structural analysis revealed that the neutralizing ability of cross-reactive antibodies was reserved only for those with an elongated CDRH3 that extends the antiparallel beta-sheet RBD core and orients the antibody light chain to obstruct ACE2-RBD interactions. These results identify a structurally defined pathway for vaccine strategies eliciting escape-resistant SARS-CoV-2 neutralizing antibodies.
Asunto(s)
Betacoronavirus/fisiología , Vacunas contra la COVID-19/inmunología , Infecciones por Coronavirus/inmunología , Coronavirus Relacionado al Síndrome Respiratorio Agudo Severo/fisiología , Glicoproteína de la Espiga del Coronavirus/metabolismo , Animales , Anticuerpos Neutralizantes/metabolismo , Anticuerpos Antivirales/metabolismo , Secuencia Conservada/genética , Evolución Molecular , Humanos , Inmunización , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Unión Proteica , Dominios Proteicos/genética , Glicoproteína de la Espiga del Coronavirus/genética , Glicoproteína de la Espiga del Coronavirus/inmunología , Desarrollo de VacunasRESUMEN
To monitor infection by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and successful vaccination against coronavirus disease 2019 (COVID-19), the kinetics of neutralizing or blocking anti-SARS-CoV-2 antibody titers need to be assessed. Here, we report the development of a quick and inexpensive surrogate SARS-CoV-2 blocking assay (SUBA) using immobilized recombinant human angiotensin-converting enzyme 2 (hACE2) and human cells expressing the native form of surface SARS-CoV-2 spike protein. Spike protein-expressing cells bound to hACE2 in the absence or presence of blocking antibodies were quantified by measuring the optical density of cell-associated crystal violet in a spectrophotometer. The advantages are that SUBA is a fast and inexpensive assay, which does not require biosafety level 2- or 3-approved laboratories. Most importantly, SUBA detects blocking antibodies against the native trimeric cell-bound SARS-CoV-2 spike protein and can be rapidly adjusted to quickly pre-screen already approved therapeutic antibodies or sera from vaccinated individuals for their ACE2 blocking activities against any emerging SARS-CoV-2 variants.
Asunto(s)
Anticuerpos Bloqueadores/sangre , Anticuerpos Neutralizantes/sangre , Anticuerpos Antivirales/análisis , Prueba Serológica para COVID-19/métodos , COVID-19/diagnóstico , Citometría de Flujo/métodos , Anticuerpos Bloqueadores/inmunología , Anticuerpos Neutralizantes/inmunología , COVID-19/inmunología , Humanos , SARS-CoV-2 , Glicoproteína de la Espiga del Coronavirus/inmunologíaRESUMEN
Long-lived antibody-secreting plasma cells are essential to establish humoral memory against pathogens. While a regulatory transcription factor network has been established in plasma cell differentiation, the regulatory role of miRNAs remains enigmatic. We have recently identified miR-148a as the most abundant miRNA in primary mouse and human plasma cells. To determine whether this plasma cell signature miRNA controls the in vivo development of B cells into long-lived plasma cells, we established mice with genomic, conditional, and inducible deletions of miR-148a. The analysis of miR-148a-deficient mice revealed reduced serum Ig, decreased numbers of newly formed plasmablasts and reduced CD19-negative, CD93-positive long-lived plasma cells. Transcriptome and metabolic analysis revealed an impaired glucose uptake, a reduced oxidative phosphorylation-based energy metabolism, and an altered abundance of homing receptors CXCR3 (increase) and CXCR4 (reduction) in miR-148a-deficient plasma cells. These findings support the role of miR-148a as a positive regulator of the maintenance of long-lived plasma cells.
Asunto(s)
Diferenciación Celular/genética , Metabolismo Energético , Regulación de la Expresión Génica , MicroARNs/genética , Células Plasmáticas/metabolismo , Animales , Antígenos CD19/metabolismo , Linfocitos B/citología , Linfocitos B/inmunología , Linfocitos B/metabolismo , Biomarcadores , Médula Ósea/inmunología , Médula Ósea/metabolismo , Diferenciación Celular/inmunología , Supervivencia Celular/genética , Supervivencia Celular/inmunología , Epítopos de Linfocito B/inmunología , Técnicas de Silenciamiento del Gen , Inmunofenotipificación , Recuento de Linfocitos , Ratones , Ratones Noqueados , Células Plasmáticas/citología , Células Plasmáticas/inmunología , Interferencia de ARNRESUMEN
We provide a robust four-color fluorescence-based flow cytometry protocol that distinguishes viable dividing plasmablasts from nondividing plasma cells and, based on CD19 surface abundance, identifies two mature plasma cell populations in the spleen and the bone marrow of mice.
Asunto(s)
Citometría de Flujo/métodos , Inmunofenotipificación/métodos , Células Plasmáticas/clasificación , Células Plasmáticas/inmunología , Coloración y Etiquetado/métodos , Animales , Antígenos CD19/análisis , Células de la Médula Ósea/inmunología , Diferenciación Celular , Proteínas Fluorescentes Verdes , Inmunofenotipificación/instrumentación , Antígenos Comunes de Leucocito/análisis , Ratones , Factor 1 de Unión al Dominio 1 de Regulación Positiva , Bazo/inmunología , Sindecano-1/análisis , Factores de Transcripción/análisisRESUMEN
B cells undergo affinity maturation and class switch recombination of their immunoglobulin receptors during a germinal center (GC) reaction, before they differentiate into long-lived antibody-secreting plasma cells (PCs). Transcription factors such as Bach2 and Mitf are essential during this process, as they delay premature differentiation of GC B cells by repressing Blimp-1 and IRF4, two transcription factors required for terminal PC differentiation. Therefore, Bach2 and Mitf expression must be attenuated in activated B cells to allow terminal PC differentiation, but the precise mechanism remains enigmatic. Here, we provide evidence that miR-148a, a small noncoding microRNA, fosters PC differentiation and survival. Next-generation sequencing revealed that miR-148a is the most abundant microRNA in primary human and murine PCs, and its expression is upregulated in activated murine B cells and coincides with Blimp-1 synthesis. miR-148a targets Bach2, Mitf and proapoptotic factors such as PTEN and Bim. When prematurely expressed, miR-148a promotes the differentiation and survival of plasmablasts and reduces frequencies of IgG1(+) cells in primary B-cell cultures. In summary, we propose that miR-148a is a new player in the regulatory network controlling terminal PC differentiation and could, therefore, be a therapeutic target for interfering with PC differentiation and survival.
Asunto(s)
Factores de Transcripción con Cremalleras de Leucina de Carácter Básico/biosíntesis , Diferenciación Celular/genética , MicroARNs/fisiología , Factor de Transcripción Asociado a Microftalmía/biosíntesis , Células Plasmáticas/citología , Animales , Proteínas Reguladoras de la Apoptosis/biosíntesis , Linfocitos B/inmunología , Secuencia de Bases , Proteína 11 Similar a Bcl2 , Diferenciación Celular/inmunología , Supervivencia Celular , Técnicas de Silenciamiento del Gen , Centro Germinal/citología , Células HEK293 , Humanos , Cambio de Clase de Inmunoglobulina/genética , Cambio de Clase de Inmunoglobulina/inmunología , Factores Reguladores del Interferón/biosíntesis , Activación de Linfocitos/genética , Proteínas de la Membrana/biosíntesis , Ratones , MicroARNs/genética , Fosfohidrolasa PTEN/biosíntesis , Factor 1 de Unión al Dominio 1 de Regulación Positiva , Proteínas Proto-Oncogénicas/biosíntesis , Proteínas Represoras/biosíntesis , Análisis de Secuencia de ADNRESUMEN
Transgenic expression of B- and T-cell receptors (BCRs and TCRs, respectively) has been a standard tool to study lymphocyte development and function in vivo. The generation of transgenic mice is time-consuming and, therefore, a faster method to study the biology of defined lymphocyte receptors in vivo would be highly welcome. Using 2A peptide-linked multicistronic retroviral vectors to transduce stem cells, TCRs can be expressed rapidly in mice of any background. We aimed at adopting this retrogenic technology to the in vivo expression of BCRs. Using a well characterised BCR specific for hen egg lysozyme (HEL), we achieved surface expression of the retrogenically encoded BCR in a Rag-deficient pro B-cell line in vitro. In vivo, retrogenic BCRs were detectable only intracellularly but not on the surface of B cells from wild type or Rag2-deficient mice. This data, together with the fact that no BCR retrogenic mouse model has been published in the 7 years since the method was originally published for TCRs, strongly suggests that achieving BCR-expression in vivo with retrogenic technology is highly challenging if not impossible.
Asunto(s)
Receptores de Antígenos de Linfocitos B/metabolismo , Animales , Línea Celular , Células Cultivadas , Ratones , Ratones Transgénicos , Muramidasa/genética , Muramidasa/metabolismo , Receptores de Antígenos de Linfocitos B/genética , Receptores de Antígenos de Linfocitos T/genética , Receptores de Antígenos de Linfocitos T/metabolismo , TransfecciónRESUMEN
B-lymphocyte development is dictated by the protein products of functionally rearranged Ig heavy (H) and light (L) chain genes. Ig rearrangement begins in pro-B cells at the IgH locus. If pro-B cells generate a productive allele, they assemble a pre-B cell receptor complex, which signals their differentiation into pre-B cells and their clonal expansion. Pre-B cell receptor signals are also thought to contribute to allelic exclusion by preventing further IgH rearrangements. Here we show in two independent mouse models that the accumulation of a stabilized µH mRNA that does not encode µH chain protein specifically impairs pro-B cell differentiation and reduces the frequency of rearranged IgH genes in a dose-dependent manner. Because noncoding IgH mRNA is usually rapidly degraded by the nonsense-mediated mRNA decay machinery, we propose that the difference in mRNA stability allows pro-B cells to distinguish between productive and nonproductive Ig gene rearrangements and that µH mRNA may thus contribute to efficient H chain allelic exclusion.
Asunto(s)
Linfocitos B/inmunología , Cadenas Pesadas de Inmunoglobulina/genética , Biosíntesis de Péptidos , Alelos , Animales , Ratones , ARN Mensajero/genética , ARN no Traducido/genética , VDJ Recombinasas/metabolismoRESUMEN
Krüppel-like factor 2 (KLF2) controls T lymphocyte egress from lymphoid organs by regulating sphingosin-1 phosphate receptor 1 (S1Pr1). Here we show that this is not the case for B cells. Instead, KLF2 controls homeostasis of B cells in peripheral lymphatic organs and homing of plasma cells to the bone marrow, presumably by controlling the expression of ß(7)-integrin. In mice with a B cell-specific deletion of KLF2, S1Pr1 expression on B cells was only slightly affected. Accordingly, all splenic B cell subsets including B1 cells were present, but their numbers were increased with a clear bias for marginal zone (MZ) B cells. In contrast, fewer peyers patches harboring fewer B cells were found, and fewer B1 cells in the peritoneal cavity as well as recirculating B cells in the bone marrow were detected. Upon thymus-dependent immunization, IgG titers were diminished, and antigen-specific plasma cells were absent in the bone marrow, although numbers of antigen-specific splenic plasmablasts were normal. KLF2 plays also a role in determining the identity of follicular B cells, as KLF2-deficient follicular B cells showed calcium responses similar to those of MZ B cells and failed to down-regulate MZ B cell signature genes, such as CD21 and CXCR7.
Asunto(s)
Linfocitos B/citología , Factores de Transcripción de Tipo Kruppel/metabolismo , Células Plasmáticas/citología , Animales , Células de la Médula Ósea/citología , Calcio/metabolismo , Clorhidrato de Fingolimod , Eliminación de Gen , Cadenas beta de Integrinas/metabolismo , Selectina L/biosíntesis , Leucosialina/biosíntesis , Ratones , Modelos Biológicos , Glicoles de Propileno/farmacología , Receptores de IgE/biosíntesis , Receptores de Lisoesfingolípidos/metabolismo , Esfingosina/análogos & derivados , Esfingosina/farmacologíaRESUMEN
BACKGROUND: Activation-induced cytidine deaminase (AID) is a B-cell-specific DNA mutator that plays a key role in the formation of the secondary antibody repertoire in germinal center B cells. In the search for binding partners, protein coimmunoprecipitation assays are often performed, generally with agarose beads. METHODOLOGY/PRINCIPAL FINDINGS: We found that, regardless of whether cell lysates containing exogenous or endogenous AID were examined, one of two mouse AID forms bound to agarose alone. CONCLUSIONS/SIGNIFICANCE: These binding characteristics may be due to the known post-translational modifications of AID; they may also need to be considered in coimmunoprecipitation experiments to avoid false-positive results.
Asunto(s)
Citidina Desaminasa/metabolismo , Isoenzimas/metabolismo , Sefarosa/metabolismo , Secuencia de Aminoácidos , Animales , Cromatografía en Gel , Inmunoprecipitación , Ratones , Ratones Endogámicos BALB C , Datos de Secuencia Molecular , Peso MolecularRESUMEN
Precursor BCR (pre-BCR) signaling governs proliferation and differentiation of pre-B cells during B lymphocyte development. However, it is controversial as to which parts of the pre-BCR, which is composed of Igmu H chain, surrogate L chain (SLC), and Igalpha-Igbeta, are important for signal initiation. Here, we show in transgenic mice that the N-terminal non-Ig-like (unique) tail of the surrogate L chain component lambda5 is critical for enhancing pre-BCR-induced proliferation signals. Pre-BCRs with a mutated lambda5 unique tail are still transported to the cell surface, but they deliver only basal signals that trigger survival and differentiation of pre-B cells. Further, we demonstrate that the positively charged residues of the lambda5 unique tail, which are required for pre-BCR self-oligomerization, can also mediate binding to stroma cell-associated self-Ags, such as heparan sulfate. These findings establish the lambda5 unique tail as a pre-BCR-specific autoreactive signaling motif that could increase the size of the primary Ab repertoire by selectively expanding pre-B cells with functional Igmu H chains.
Asunto(s)
Linfocitos B/citología , Inmunoglobulina de Cadenas Ligeras Subrogadas/fisiología , Animales , Autoantígenos/metabolismo , Cadenas Pesadas de Inmunoglobulina , Cadenas mu de Inmunoglobulina , Ratones , Ratones Transgénicos , Receptores de Antígenos de Linfocitos B/metabolismo , Transducción de SeñalRESUMEN
Although it is generally accepted that Ig heavy chains (HC) are selected at the pre-B cell receptor (pre-BCR) checkpoint, the characteristics of a functional HC and the role of pre-BCR assembly in their selection have remained elusive. We determined the characteristics of HCs that successfully passed the pre-BCR checkpoint by examining transcripts harboring V(H)81X and J(H)4 gene segments from J(H)(+/-) and lambda5(-/-)mice. V(H)81X-J(H)4-HC transcripts isolated from cells before or in the absence of pre-BCR assembly had no distinguishing complementarity-determining region 3 traits. In contrast, transcripts isolated subsequent to passage through the pre-BCR checkpoint had distinctive complementarity-determining regions 3 of nine amino acids in length (49%) and a histidine at position 1 (73%). Hence, our data define specific structural requirements for a functional HC, which is instrumental in shaping the diverse B cell repertoire.
Asunto(s)
Aminoácidos/análisis , Regiones Determinantes de Complementariedad/biosíntesis , Cadenas Pesadas de Inmunoglobulina/biosíntesis , Cadenas mu de Inmunoglobulina/biosíntesis , Fragmentos de Péptidos/biosíntesis , Procesamiento Proteico-Postraduccional/inmunología , Aminoácidos/genética , Animales , Subgrupos de Linfocitos B/citología , Subgrupos de Linfocitos B/inmunología , Subgrupos de Linfocitos B/metabolismo , Células de la Médula Ósea/citología , Células de la Médula Ósea/inmunología , Células de la Médula Ósea/metabolismo , Diferenciación Celular/genética , Diferenciación Celular/inmunología , Membrana Celular/genética , Membrana Celular/inmunología , Membrana Celular/metabolismo , Regiones Determinantes de Complementariedad/genética , Regiones Determinantes de Complementariedad/fisiología , Reordenamiento Génico de Cadena Pesada de Linfocito B , Histidina/análisis , Histidina/genética , Cadenas Pesadas de Inmunoglobulina/genética , Cadenas Pesadas de Inmunoglobulina/fisiología , Cadenas Ligeras de Inmunoglobulina , Inmunoglobulina de Cadenas Ligeras Subrogadas , Cadenas mu de Inmunoglobulina/genética , Cadenas mu de Inmunoglobulina/fisiología , Glicoproteínas de Membrana/deficiencia , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Modelos Inmunológicos , Modelos Moleculares , Fragmentos de Péptidos/genética , Fragmentos de Péptidos/fisiología , Procesamiento Proteico-Postraduccional/genética , Estructura Terciaria de Proteína , Bazo/citología , Bazo/inmunología , Bazo/metabolismoRESUMEN
Pre-B cell receptor (pre-BCR) signals are essential for pro-B cells to mature efficiently into pre-B cells. The pre-BCR is an Ig-like transmembrane complex that is assembled from two mu H chains (mu HC) and two surrogate L chains consisting of the non-covalently associated polypeptides VpreB and lambda5. In lambda5(-/-) mice, pro-B cell maturation is impaired, but not completely blocked, implying that a mu HC induces differentiation signals in the absence of lambda5. Using a mouse model, in which transgenic mu HC expression can be controlled by tetracycline, we show that in the absence of lambda5, the transgenic mu HC promotes in vivo differentiation of pro-B cells, induces IL-7-dependent cell growth, and is expressed on the surface of pre-B cells. Our findings not only show that an incomplete pre-BCR can initiate signals, but also challenge the paradigm that an IgHC must associate with an IgLC or a SLC to gain transport and signaling competency.