Dynamic Changes in Lymphocyte Populations Establish Zebrafish as a Thymic Involution Model

The thymus is the site of T lymphocyte development and T cell education to recognize foreign, but not self, Ags. B cells also reside and develop in the thymus, although their functions are less clear. During "thymic involution," a process of lymphoid atrophy and adipose replacement linked to sexual maturation, thymocytes decline. However, thymic B cells decrease far less than T cells, such that B cells comprise ∼1% of human neonatal thymocytes but up to ∼10% in adults. All jawed vertebrates possess a thymus, and we and others have shown zebrafish (Danio rerio) also have thymic B cells. In this article, we investigated the precise identities of zebrafish thymic T and B cells and how they change with involution. We assessed the timing and specific details of zebrafish thymic involution using multiple lymphocyte-specific, fluorophore-labeled transgenic lines, quantifying the changes in thymic T- and B-lymphocytes pre- versus postinvolution. Our results prove that, as in humans, zebrafish thymic B cells increase relative to T cells postinvolution. We also performed RNA sequencing on D. rerio thymic and marrow lymphocytes of four novel double-transgenic lines, identifying distinct populations of immature T and B cells. Collectively, this is, to our knowledge, the first comprehensive analysis of zebrafish thymic involution, demonstrating its similarity to human involution and establishing the highly genetically manipulatable zebrafish model as a template for involution studies.

Dynamic Changes in Lymphocyte Populations Establish Zebrafish as a Thymic Involution Model

The thymus is the site of T lymphocyte development and T cell education to recognize foreign, but not self, antigens. B cells also reside and develop in the thymus, although their functions are less clear. During 'thymic involution,' a process of lymphoid atrophy and adipose replacement linked to sexual maturation, thymocytes decline. However, thymic B cells decrease far less than T cells, such that B cells comprise ~1% of human neonatal thymocytes, but up to ~10% in adults. All jawed vertebrates possess a thymus, and we and others have shown zebrafish (Danio rerio) also have thymic B cells. Here, we investigated the precise identities of zebrafish thymic T and B cells and how they change with involution. We assessed the timing and specific details of zebrafish thymic involution using multiple lymphocyte-specific, fluorophore-labeled transgenic lines, quantifying the changes in thymic T- and B-lymphocytes pre- vs. post-involution. Our results prove that, as in humans, zebrafish thymic B cells increase relative to T cells post-involution. We also performed RNA sequencing (RNA-seq) on D. rerio thymic and marrow lymphocytes of four novel double-transgenic lines, identifying distinct populations of immature T and B cells. Collectively, this is the first comprehensive analysis of zebrafish thymic involution, demonstrating its similarity to human involution, and establishing the highly genetically-manipulatable zebrafish model as a template for involution studies.

Association of Combined Focal 22q11.22 Deletion and IKZF1 Alterations With Outcomes in Childhood Acute Lymphoblastic Leukemia

Importance

Alterations in the IKZF1 gene drive B-cell acute lymphoblastic leukemia (B-ALL) but are not routinely used to stratify patients by risk because of inconsistent associations with outcomes. We describe a novel deletion in 22q11.22 that was consistently associated with very poor outcomes in patients with B-ALL with IKZF1 alterations.

Objective

To determine whether focal deletions within the λ variable chain region in chromosome 22q11.22 were associated with patients with B-ALL with IKZF1 alterations with the highest risk of relapse and/or death.

Design, Setting, and Participants

This cohort study included 1310 primarily high-risk pediatric patients with B-ALL who were taken from 6 independent clinical cohorts, consisting of 3 multicenter cohorts (AALL0232 [2004-2011], P9906 [2000-2003], and patients with Down syndrome who were pooled from national and international studies) and 3 single-institution cohorts (University of Utah [Salt Lake City], Children's Hospital of Philadelphia [Philadelphia, Pennsylvania], and St. Jude Children's Hospital [Memphis, Tennessee]). Data analysis began in 2011 using patients from the older studies first, and data analysis concluded in 2021.

Exposures

Focal 22q11.22 deletions.

Main Outcomes and Measures

Event-free and overall survival was investigated. The hypothesis that 22q11.22 deletions stratified the prognostic effect of IKZF1 alterations was formulated while investigating nearby deletions in VPREB1 in 2 initial cohorts (n = 270). Four additional cohorts were then obtained to further study this association (n = 1040).

Results

This study of 1310 patients with B-ALL (717 male [56.1%] and 562 female patients [43.9%]) found that focal 22q11.22 deletions are frequent (518 of 1310 [39.5%]) in B-ALL and inconsistent with physiologic V(D)J recombination. A total of 299 of 1310 patients with B-ALL had IKZF1 alterations. Among patients with IKZF1 alterations, more than half shared concomitant focal 22q11.22 deletions (159 of 299 [53.0%]). Patients with combined IKZF1 alterations and 22q11.22 deletions had worse outcomes compared with patients with IKZF1 alterations and wild-type 22q11.22 alleles in every cohort examined (combined cohorts: 5-year event-free survival rates, 43.3% vs 68.5%; hazard ratio [HR], 2.18; 95% CI, 1.54-3.07; P < .001; 5-year overall survival rates, 66.9% vs 83.9%; HR, 2.05; 95% CI, 1.32-3.21; P = .001). While 22q11.22 deletions were not prognostic in patients with wild-type IKZF1 , concomitant 22q11.22 deletions in patients with IKZF1 alterations stratified outcomes across additional risk groups, including patients who met the IKZF1plus criteria, and maintained independent significance in multivariate analysis for event-free survival (HR, 2.05; 95% CI, 1.27-3.29; P = .003) and overall survival (HR, 1.83; 95% CI, 1.01-3.34; P = .05).

Conclusions and Relevance

This cohort study suggests that 22q11.22 deletions identify patients with B-ALL and IKZF1 alterations who have very poor outcomes and may offer a new genetic biomarker to further refine B-ALL risk stratification and treatment strategies.

Zebrafish B cell acute lymphoblastic leukemia: new findings in an old model

Acute lymphoblastic leukemia (ALL) is the most common pediatric, and ninth most common adult, cancer. ALL can develop in either B or T lymphocytes, but B-lineage ALL (B-ALL) exceeds T-ALL clinically. As for other cancers, animal models allow study of the molecular mechanisms driving ALL. Several zebrafish (Danio rerio) T-ALL models have been reported, but until recently, robust D. rerio B-ALL models were not described. Then, D. rerio B-ALL was discovered in two related zebrafish transgenic lines; both were already known to develop T-ALL. Here, we report new B-ALL findings in one of these models, fish expressing transgenic human MYC (hMYC). We describe B-ALL incidence in a large cohort of hMYC fish, and show B-ALL in two new lines where T-ALL does not interfere with B-ALL detection. We also demonstrate B-ALL responses to steroid and radiation treatments, which effect ALL remissions, but are usually followed by prompt relapses. Finally, we report gene expression in zebrafish B lymphocytes and B-ALL, in both bulk samples and single B- and T-ALL cells. Using these gene expression profiles, we compare differences between the two new D. rerio B-ALL models, which are both driven by transgenic mammalian MYC oncoproteins. Collectively, these new data expand the utility of this new vertebrate B-ALL model.

Targeted sequencing of candidate genes of dyslipidemia in Punjabi Sikhs: Population-specific rare variants in GCKR promote ectopic fat deposition

Dyslipidemia is a well-established risk factor for cardiovascular diseases. Although, advances in genome-wide technologies have enabled the discovery of hundreds of genes associated with blood lipid phenotypes, most of the heritability remains unexplained. Here we performed targeted resequencing of 13 bona fide candidate genes of dyslipidemia to identify the underlying biological functions. We sequenced 940 Sikh subjects with extreme serum levels of hypertriglyceridemia (HTG) and 2,355 subjects were used for replication studies; all 3,295 participants were part of the Asian Indians Diabetic Heart Study. Gene-centric analysis revealed burden of variants for increasing HTG risk in GCKR (p = 2.1x10-5), LPL (p = 1.6x10-3) and MLXIPL (p = 1.6x10-2) genes. Of these, three missense and damaging variants within GCKR were further examined for functional consequences in vivo using a transgenic zebrafish model. All three mutations were South Asian population-specific and were largely absent in other multiethnic populations of Exome Aggregation Consortium. We built different transgenic models of human GCKR with and without mutations and analyzed the effects of dietary changes in vivo. Despite the short-term of feeding, profound phenotypic changes were apparent in hepatocyte histology and fat deposition associated with increased expression of GCKR in response to a high fat diet (HFD). Liver histology of the GCKRmut showed severe fatty metamorphosis which correlated with ~7 fold increase in the mRNA expression in the GCKRmut fish even in the absence of a high fat diet. These findings suggest that functionally disruptive GCKR variants not only increase the risk of HTG but may enhance ectopic lipid/fat storage defects in absence of obesity and HFD. To our knowledge, this is the first transgenic zebrafish model of a putative human disease gene built to accurately assess the influence of genetic changes and their phenotypic consequences in vivo.

Isolating Malignant and Non-Malignant B Cells from lck:eGFP Zebrafish

Zebrafish (Danio rerio) are a powerful model to study lymphocyte development. Like mammals, D. rerio possess an adaptive immune system that includes B and T lymphocytes. Studies of zebrafish lymphopoiesis are difficult because antibodies recognizing D. rerio cell surface markers are generally not available, complicating isolation and characterization of different lymphocyte populations, including B-lineage cells. Transgenic lines with lineage-specific fluorophore expression are often used to circumvent this challenge. The transgenic lck:eGFP line has been used to study D. rerio T cell development, and has also been utilized to model T cell development and acute lymphoblastic leukemia (T-ALL). Although lck:eGFP fish have been widely used to analyze the T-lineage, they have not been used to study B cells. Recently, we discovered that many zebrafish B cells also express lck, albeit at lower levels. Consequently, lck:eGFP B cells likewise express low levels of GFP. Based on this finding, we developed a protocol to purify B-lineage cells from lck:eGFP zebrafish, which we report here. Our method describes how to utilize a fluorescent-activated cell sorter (FACS) to purify B cells from lck:eGFP fish or related lines, such as double-transgenic rag2:hMYC; lck:eGFP fish. In these lines, B cells, particularly immature B cells, express GFP at low but detectable levels, allowing them to be distinguished from T cells, which express GFP highly. B cells can be isolated from marrow, thymus, spleen, blood, or other tissues. This protocol provides a new method to purify D. rerio B cells, enabling studies focused on topics like B cell development and B lymphocyte malignancies.

Simultaneous B and T cell acute lymphoblastic leukemias in zebrafish driven by transgenic MYC: implications for oncogenesis and lymphopoiesis

Precursor-B cell acute lymphoblastic leukemia (pre-B ALL) is the most common pediatric cancer, but there are no useful zebrafish pre-B ALL models. We describe the first highly- penetrant zebrafish pre-B ALL, driven by human MYC. Leukemias express B lymphoblast-specific genes and are distinct from T cell ALL (T-ALL)—which these fish also develop. Zebrafish pre-B ALL shares in vivo features and expression profiles with human pre-B ALL, and these profiles differ from zebrafish T-ALL or normal B and T cells. These animals also exhibit aberrant lymphocyte development. As the only robust zebrafish pre-B ALL model and only example where T-ALL also develops, this model can reveal differences between MYC-driven pre-B vs. T-ALL and be exploited to discover novel pre-B ALL therapies.

Molecular genetics of childhood, adolescent and young adult non-Hodgkin lymphoma

Molecular genetic abnormalities are ubiquitous in non-Hodgkin lymphoma (NHL), but genetic changes are not yet used to define specific lymphoma subtypes. Certain recurrent molecular genetic abnormalities in NHL underlie molecular pathogenesis and/or are associated with prognosis or represent potential therapeutic targets. Most molecular genetic studies of B- and T-NHL have been performed on adult patient samples, and the relevance of many of these findings for childhood, adolescent and young adult NHL remains to be demonstrated. In this review, we focus on NHL subtypes that are most common in young patients and emphasize features actually studied in younger NHL patients. This approach highlights what is known about NHL genetics in young patients but also points to gaps that remain, which will require cooperative efforts to collect and share biological specimens for genomic and genetic analyses in order to help predict outcomes and guide therapy in the future.

Impact of persistent minimal residual disease post-consolidation therapy in children and adolescents with advanced Burkitt leukaemia: a Children's Oncology Group Pilot Study Report

Patient-specific primers from 10 children/adolescents with Burkitt leukaemia (BL) ± central nervous system disease who were treated with French-British-American/Lymphome Malins de Burkitt 96 C1 plus rituximab were developed from diagnostic blood/bone marrow. Minimal residual disease (MRD) was assessed by real-time polymerase chain reaction at the end of induction (EOI) and consolidation (EOC). Seventy per cent (7/10) and 71% (5/7) were MRD-positive at EOI and EOC, respectively, with no disease recurrences. MRD after induction and consolidation did not predict relapse and subsequent therapy appeared to eliminate MRD. Thus, assessing MRD at a later time point is warranted in future trials to determine its clinical significance.

Unusual fluorescent granulomas and myonecrosis in Danio rerio infected by the microsporidian pathogen Pseudoloma neurophilia

Abstract Zebrafish are a powerful model organism to study disease. Like other animal models, Danio rerio colonies are at risk of pathogenic infection. Microsporidia, a group of intracellular fungus-like parasites, are one potential threat. Microsporidian spores germinate and spread causing pathological changes in the central nervous system, skeletal muscle, and other anatomic sites. Infection can impair breeding, cause other morbidities, and ultimately be lethal. Previously, detecting microsporidia in zebrafish has required sacrificing animals for histopathologic analysis or microscopic examination of fresh tissues. Here, we show that fish with microsporidial infection often have autofluorescent nodules, and we demonstrate infectious spread from nodule-bearing fish to healthy D. rerio. Histologic analyses revealed that fluorescent nodules are granulomatous lesions composed of spores, degenerating muscle, and inflammatory cells. Additional histologic staining verified that microsporidia were present, specifically, Pseudoloma neurophilia. Polymerase chain reaction (PCR)-based testing confirmed the presence of P. neurophilia. Further PCR testing excluded infection by another common zebrafish microsporidial parasite, Pleistophora hyphessobryconis. Collectively, these studies show that P. neurophilia can induce skeletal muscle granulomas in D. rerio, a previously unknown finding. Moreover, since granulomas autofluoresce, microscopic screening for P. neurophilia infection is feasible in live fish, avoiding the need to sacrifice fish for surveillance for this pathogen.

Danio rerio: Small Fish Making a Big Splash in Leukemia

Zebrafish (Danio rerio) are widely used for developmental biology studies. In the past decade, D. rerio have become an important oncology model as well. Leukemia is one type of cancer where zebrafish are particularly valuable. As vertebrates, fish have great anatomic and biologic similarity to humans, including their hematopoietic and immune systems. As an experimental platform, D. rerio offer many advantages that mammalian models lack. These include their ease of genetic manipulation, capacity for imaging, and suitability for large-scale phenotypic and drug screens. In this review, we present examples of these strategies and others to illustrate how zebrafish have been and can be used to study leukemia. Besides appraising the techniques researchers apply and introducing the leukemia models they have created, we also highlight recent and exciting discoveries made using D. rerio with an eye to where the field is likely headed.

UNC569, a novel small-molecule mer inhibitor with efficacy against acute lymphoblastic leukemia in vitro and in vivo

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. Although survival rates have improved, patients with certain biologic subtypes still have suboptimal outcomes. Current chemotherapeutic regimens are associated with short- and long-term toxicities and novel, less toxic therapeutic strategies are needed. Mer receptor tyrosine kinase is ectopically expressed in ALL patient samples and cell lines. Inhibition of Mer expression reduces prosurvival signaling, increases chemosensitivity, and delays development of leukemia in vivo, suggesting that Mer tyrosine kinase inhibitors are excellent candidates for targeted therapies. Brain and spinal tumors are the second most common malignancies in childhood. Multiple chemotherapy approaches and radiotherapies have been attempted, yet overall survival remains dismal. Mer is also abnormally expressed in atypical teratoid/rhabdoid tumors (AT/RT), providing a rationale for targeting Mer as a therapeutic strategy. We have previously described UNC569, the first small-molecule Mer inhibitor. This article describes the biochemical and biologic effects of UNC569 in ALL and AT/RT. UNC569 inhibited Mer activation and downstream signaling through ERK1/2 and AKT, determined by Western blot analysis. Treatment with UNC569 reduced proliferation/survival in liquid culture, decreased colony formation in methylcellulose/soft agar, and increased sensitivity to cytotoxic chemotherapies. MYC transgenic zebrafish with T-ALL were treated with UNC569 (4 μmol/L for two weeks). Fluorescence was quantified as indicator of the distribution of lymphoblasts, which express Mer and enhanced GFP. UNC569 induced more than 50% reduction in tumor burden compared with vehicle- and mock-treated fish. These data support further development of Mer inhibitors as effective therapies in ALL and AT/RT.

Efficacy of rituximab plus FAB group C chemotherapy without CNS radiation in CNS-positive pediatric Burkitt lymphoma/leukemia: A report from the Children’s Oncology Group

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Background: Historically, CNS-positive (CNS+) mature B-NHL in children and adolescents has been associated with a dismal outcome (Miles/Cairo, Br J Haematol, 2012). Adding CNS radiation and high-dose MTX and cytarabine to group C therapy for children with CNS+ B-NHL yielded a 77% 5-yr EFS in LMB89 (Patte et al., Blood, 2001). An ensuing FAB/LMB96 trial replaced cranial radiation with further HD-MTX and intrathecal therapy with similar results (75% 4-yr EFS) (Cairo et al., Blood, 2007). Here, patients with marrow and CNS+ disease fared worse than isolated CNS+ (61% vs. 83% 4-yr EFS, p<0.001), with >50% of CNS+ patients who progressed or recurred having systemic, but not CNS, relapse. Rituximab, a chimeric anti-CD20 antibody, improved EFS, PFS, and OS when added to chemotherapy for adults with DLBCL (Coiffier et al., N Engl J Med, 2002; Pfreundschuh et al., Lancet Oncol, 2006). We tested whether adding rituximab to FAB group C chemotherapy in pediatric patients with CNS+ B-NHL was safe and efficacious. Methods: Children and adolescents (<21 yrs.) with CNS+ B-NHL received FAB group C1 therapy (Cairo et al., Blood, 2007). Rituximab (375 mg/m2/dose) was given twice in COPADM courses 1 & 2 and once in CYVE courses (Cairo et al., ASCO, 2010). CSF blasts (>1), cranial nerve palsy (CNP), intra-cerebral mass (ICM), and/or parameningeal extension (PME) defined cases as CNS+. Results: Of 40 eligible Group C patients,15 (38%) were CNS+; all 15 had Burkitt morphology. Eight CNS+ patients were CSF+ [WBC median 35 (range 1-1104)] with 6 cases CNP+, 4 PME+, and 1 ICM+. No adverse events were attributed to rituximab. Fourteen of 15 CNS+ patients (93%) are alive and disease-free. Of 7 BM-/CNS+ patients, 100% are NED. In BM+/CNS+ cases, 7/8 (88%) are NED, with one patient progressing with systemic and CNS disease. Conclusions: Addition of rituximab to group C FAB therapy was well tolerated. Outcomes in this small cohort of 15 children and adolescents with CNS+ BL (93%) suggest that adding rituximab to FAB group C therapy without CNS radiation may reduce systemic relapse. Large randomized studies are warranted to test this hypothesis in this previously high-risk clinical subgroup.

Pediatric T- and NK-cell lymphomas: new biologic insights and treatment strategies

T- and natural killer (NK)-cell lymphomas are challenging childhood neoplasms. These cancers have varying presentations, vast molecular heterogeneity, and several are quite unusual in the West, creating diagnostic challenges. Over 20 distinct T- and NK-cell neoplasms are recognized by the 2008 World Health Organization classification, demonstrating the diversity and potential complexity of these cases. In pediatric populations, selection of optimal therapy poses an additional quandary, as most of these malignancies have not been studied in large randomized clinical trials. Despite their rarity, exciting molecular discoveries are yielding insights into these clinicopathologic entities, improving the accuracy of our diagnoses of these cancers, and expanding our ability to effectively treat them, including the use of new targeted therapies. Here, we summarize this fascinating group of lymphomas, with particular attention to the three most common subtypes: T-lymphoblastic lymphoma, anaplastic large cell lymphoma, and peripheral T-cell lymphoma-not otherwise specified. We highlight recent findings regarding their molecular etiologies, new biologic markers, and cutting-edge therapeutic strategies applied to this intriguing class of neoplasms.

Shared acquired genomic changes in zebrafish and human T-ALL

T-cell acute lymphoblastic leukemia (T-ALL) is a challenging clinical entity with high rates of induction failure and relapse. To discover the genetic changes occurring in T-ALL, and those contributing to relapse, we studied zebrafish (Danio rerio) T-ALL samples using array comparative genomic hybridization (aCGH). We performed aCGH on 17 T-ALLs from four zebrafish T-ALL models, and evaluated similarities between fish and humans by comparing all D. rerio genes with copy number aberrations (CNAs) with a cohort of 75 published human T-ALLs analyzed by aCGH. Within all D. rerio CNAs, we identified 893 genes with human homologues and found significant overlap (67%) with the human CNA dataset. In addition, when we restricted our analysis to primary T-ALLs (14 zebrafish and 61 human samples), 10 genes were recurrently altered in > 3 zebrafish cancers and ≥ 4 human cases, suggesting a conserved role for these loci in T-ALL transformation across species. We also conducted iterative allo-transplantation with three zebrafish malignancies. This technique selects for aggressive disease, resulting in shorter survival times in successive transplant rounds and modeling refractory and relapsed human T-ALL. Fifty-five percent of original CNAs were preserved after serial transplantation, demonstrating clonality between each primary and passaged leukemia. Cancers acquired an average of 34 new CNAs during passaging. Genes in these loci may underlie the enhanced malignant behavior of these neoplasias. We also compared genes from CNAs of passaged zebrafish malignancies with aCGH results from 50 human T-ALL patients who failed induction, relapsed or would eventually relapse. Again, many genes (88/164) were shared by both datasets. Further, nine recurrently altered genes in passaged D. rerio T-ALL were also found in multiple human T-ALL cases. These results suggest that zebrafish and human T-ALLs are similar at the genomic level, and are governed by factors that have persisted throughout evolution.

Heritable T-cell malignancy models established in a zebrafish phenotypic screen

T cell neoplasias are common in pediatric oncology, and include acute lymphoblastic leukemia (T-ALL) and lymphoblastic lymphoma (T-LBL). These cancers have worse prognoses than their B cell counterparts, and their treatments carry significant morbidity. While many pediatric malignancies have characteristic translocations, most T lymphocyte-derived diseases lack cytogenetic hallmarks. Lacking these informative lesions, insight into their molecular pathogenesis is less complete. Although dysregulation of the NOTCH1 pathway occurs in a substantial fraction of cases, many other genetic lesions of T cell malignancy have not yet been determined. To address this deficiency, we pioneered a phenotype-driven forward-genetic screen in zebrafish (Danio rerio). Using transgenic fish with T lymphocyte-specific expression of enhanced green fluorescent protein (EGFP), we performed chemical mutagenesis, screened animals for GFP⁺ tumors, and identified multiple lines with a heritable predisposition to T cell malignancy. In each line, patterns of infiltration and morphologic appearance resembled human T-ALL and T-LBL. T cell receptor analyses confirmed their clonality. Malignancies were transplantable and contained leukemia-initiating cells (LIC), like their human correlates. In summary, we have identified multiple zebrafish mutants that recapitulate human T cell neoplasia and show heritable transmission. These vertebrate models provide new genetic platforms for the study of these important human cancers.

Metamizole use by Latino immigrants: a common and potentially harmful home remedy

A 4-year-old boy presented with fever, septic arthritis, and persistent neutropenia. Bone marrow biopsy revealed no evidence of neoplasia. Additional history disclosed that the patient had been given metamizole for pain before onset of his illness. Metamizole, a nonsteroidal antiinflammatory agent, is prohibited in the United States because of the risk of agranulocytosis but is widely used in Mexico and other countries. The increasing number of Latinos in the United States and the extensive cross-border transfer of medicines raise concerns that metamizole use and associated complications may become more frequent. After identification of the index patient, additional inquiry revealed that the patient's mother was hospitalized previously for overwhelming sepsis associated with metamizole use. These cases prompted an investigation of metamizole use in an urban pediatric clinic, which revealed that 35% of Spanish-speaking Latino families had used metamizole; 25% of these families had purchased the medication in the United States. We conclude that metamizole use is common and may be underrecognized in immigrant Latino patients. Physicians in the United States, especially those who practice primary care, hematology/oncology, and infectious diseases, must be aware of the availability and use of metamizole in specific patient populations and its potential for harmful side effects.

Identification of centerin: a novel human germinal center B cell-restricted serpin

For naive B cells to mature in response to antigen triggering and become either plasma cells or memory B cells, a complex array of events takes place within germinal centers (GC) of secondary lymphoid organs. With the long-term objective of defining and characterizing molecules that control the generation of GC, we have subtracted RNA messages derived from highly purified B cells at the follicular mantle stage of differentiation from GC B cells. Using this approach, we have identified a novel molecule, centerin, belonging to the family of serine-protease inhibitors or serpins. Transcription of centerin is highly restricted to GC B cells and their malignant counterparts, Burkitt's lymphoma lines. The putative centerin protein shares the highest sequence identity with thyroxine-binding globulin and possesses arginine/serine at its P1/P1' active site, suggesting that it interacts with a trypsin-like protease(s). In addition, several other sequence features of centerin also indicate that it serves as a bonafide protease inhibitor. Finally, we demonstrate differentially up-regulated transcription of this novel gene by resting, naive B cells stimulated in vitro via CD40 signaling, while Staphylococcus aureus Cowan strain-mediated B cell activation fails to generate this reponse. Because CD40 signaling is required for naive B cells to enter the GC reaction and for GC B cells to survive, it is likely that centerin plays a role in the development and/or sustaining of GC.

OPG/FDCR-1, a TNF Receptor Family Member, Is Expressed in Lymphoid Cells and Is Up-Regulated by Ligating CD40

We have cloned a TNFR family member from a follicular dendritic cell (FDC)-like cell line, FDC-1. This molecule, FDC-derived receptor-1 (FDCR-1), is identical to osteoprotegerin (OPG), a soluble cytokine that regulates osteoclast differentiation. Recently, OPG/FDCR-1 has been characterized as a second receptor for receptor activator of NF-κB ligand (RANKL)/TNF-related activation-induced cytokine (TRANCE), a primarily T-cell restricted TNF family member that augments dendritic cell (DC) function. In this report, we demonstrate that OPG/FDCR-1 is membrane bound on the surface of transfected baby hamster kidney (BHK) and untransfected FDC-1 cells. We also found a restricted OPG/FDCR-1 expression pattern in lymphoid cells, specifically in B cells, DCs and FDC-enriched fractions, which in B cells and DCs is up-regulated by CD40 stimulation. Because OPG/FDCR-1 shares some properties with RANK, the first RANKL/TRANCE receptor, we discuss how the balance between RANK and OPG/FDCR-1 expression could influence immune responses and, ultimately, germinal center formation.

OPG/FDCR-1, a TNF receptor family member, is expressed in lymphoid cells and is up-regulated by ligating CD40

We have cloned a TNFR family member from a follicular dendritic cell (FDC)-like cell line, FDC-1. This molecule, FDC-derived receptor-1 (FDCR-1), is identical to osteoprotegerin (OPG), a soluble cytokine that regulates osteoclast differentiation. Recently, OPG/FDCR-1 has been characterized as a second receptor for receptor activator of NF-kappaB ligand (RANKL)/TNF-related activation-induced cytokine (TRANCE), a primarily T-cell restricted TNF family member that augments dendritic cell (DC) function. In this report, we demonstrate that OPG/FDCR-1 is membrane bound on the surface of transfected baby hamster kidney (BHK) and untransfected FDC-1 cells. We also found a restricted OPG/FDCR-1 expression pattern in lymphoid cells, specifically in B cells, DCs and FDC-enriched fractions, which in B cells and DCs is up-regulated by CD40 stimulation. Because OPG/FDCR-1 shares some properties with RANK, the first RANKL/TRANCE receptor, we discuss how the balance between RANK and OPG/FDCR-1 expression could influence immune responses and, ultimately, germinal center formation.