Differential Regulation of B Cell Development, Activation, and Death by the Src Homology 2 Domain–Containing 5′ Inositol Phosphatase (Ship)

Although the Src homology 2 domain–containing 5′ inositol phosphatase (SHIP) is a well-known mediator of inhibitory signals after B cell antigen receptor (BCR) coaggregation with the low affinity Fc receptor, it is not known whether SHIP functions to inhibit signals after stimulation through the BCR alone. Here, we show using gene-ablated mice that SHIP is a crucial regulator of BCR-mediated signaling, B cell activation, and B cell development. We demonstrate a critical role for SHIP in termination of phosphatidylinositol 3,4,5-triphosphate (PI[3,4,5]P3) signals that follow BCR aggregation. Consistent with enhanced PI(3,4,5)P3 signaling, we find that splenic B cells from SHIP-deficient mice display enhanced sensitivity to BCR-mediated induction of the activation markers CD86 and CD69. We further demonstrate that SHIP regulates the rate of B cell development in the bone marrow and spleen, as B cell precursors from SHIP-deficient mice progress more rapidly through the immature and transitional developmental stages. Finally, we observe that SHIP-deficient B cells have increased resistance to BCR-mediated cell death. These results demonstrate a central role for SHIP in regulation of BCR signaling and B cell biology, from signal driven development in the bone marrow and spleen, to activation and death in the periphery.

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A Dual Role for Src Homology 2 Domain–Containing Inositol-5-Phosphatase (Ship) in Immunity

Journal of Experimental Medicine ◽

10.1084/jem.191.5.781 ◽

2000 ◽

Vol 191 (5) ◽

pp. 781-794 ◽

Cited By ~ 115

Author(s):

Cheryl D. Helgason ◽

Christian P. Kalberer ◽

Jacqueline E. Damen ◽

Suzanne M. Chappel ◽

Nicolas Pineault ◽

...

Keyword(s):

B Cells ◽

B Cell ◽

Cell Development ◽

B Cell Development ◽

Lymphoid Development ◽

Src Homology 2 ◽

Src Homology ◽

Src Homology 2 Domain ◽

B Lymphoid

In this report, we demonstrate that the Src homology 2 domain–containing inositol-5-phosphatase (SHIP) plays a critical role in regulating both B cell development and responsiveness to antigen stimulation. SHIP−/− mice exhibit a transplantable alteration in B lymphoid development that results in reduced numbers of precursor B (fraction C) and immature B cells in the bone marrow. In vitro, purified SHIP−/− B cells exhibit enhanced proliferation in response to B cell receptor stimulation in both the presence and absence of Fcγ receptor IIB coligation. This enhancement is associated with increased phosphorylation of both mitogen-activated protein kinase and Akt, as well as with increased survival and cell cycling. SHIP−/− mice manifest elevated serum immunoglobulin (Ig) levels and an exaggerated IgG response to the T cell–independent type 2 antigen trinitrophenyl Ficoll. However, only altered B cell development was apparent upon transplantation into nonobese diabetic–severe combined immunodeficient (NOD/SCID) mice. The in vitro hyperresponsiveness, together with the in vivo findings, suggests that SHIP regulates B lymphoid development and antigen responsiveness by both intrinsic and extrinsic mechanisms.

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The POZ/BTB Domain Transcription Factor Miz-1 (Zbtb17) Is Required during Early B Cell Development for the Survival of B-Cell Progenitors and Is Essential for the Formation of Mature Follicular B Cells

Blood ◽

10.1182/blood.v112.11.703.703 ◽

2008 ◽

Vol 112 (11) ◽

pp. 703-703

Author(s):

Christian Kosan ◽

Tarik Moroy

Keyword(s):

Bone Marrow ◽

Transcription Factor ◽

B Cells ◽

B Cell ◽

Cell Development ◽

B Cell Development ◽

Marginal Zone B Cells ◽

Btb Domain ◽

Follicular B Cells ◽

Deficient Mice

Abstract B-cell development takes place in the bone marrow and is defined by a number of sequential steps that include the up-regulation of CD19, the rearrangement of immunoglobulin heavy and light chain genes (V(D)J recombination) and the expression of surface immunoglobulin. The early steps are regulated by cytokine signaling and the hierarchical expression of transcription factors, among them EBF, Pax5 and E2A and any interference with these critical elements leads to partial or total abrogation of B cell development. Here we present evidence that the POZ/BTB domain transcription factor Miz-1 (Zbtb17) represents an important novel regulator of the early development of follicular B cells. We have used gene targeting in mice to generate a non-functional allele of Miz-1 in all hematopoietic cells. In these mice, the development of adult follicular B cells is almost entirely abrogated, whereas the formation of marginal zone B-cells remain unaffected. Miz-1 deficiency correlated with the absence of CD19+ pro B-cells from the bone marrow and a block at the transition of the pre-pro-B cell to the pro-B cell stage. Although common lymphoid progenitors (CLPs) that are at the origin of B-cell development were present in Miz-1 deficient mice, they showed decreased expression of E2A, EBF and Pax5 compared to their wild type counterparts. Moreover, they were unable to differentiate in culture into more mature B cells even on stroma cells (OP9) and the presence or absence of IL-7. Interestingly, a forced expression of EBF or PAX5 in Miz-1 deficient progenitor cells did not rescue this phenotype. Furthermore, fetal B cell development, which has been shown to depend on EBF and Pax5, is not altered in Miz-1 deficient mice, suggesting that Miz-1 acts in a pathway that is independent of these critical B-cell regulators. In contrast, however, to EBF and Paxc5, the co-expression of a Bcl-2 transgene almost completely restored the development of more mature CD19+ or IgM+ B-cells in Miz-1 deficient mice. This indicated that Miz-1 is implicated in the regulation of cell survival at early stages of B cell development. Since it has been shown before that Bcl-2 is a downstream effector of Miz-1, it is conceivable that Miz-1 regulates Bcl-2 in the early B cell precursors, possibly as an element of the IL-7 signaling pathway, and thereby ensures their survival and proper development. We conclude that Miz-1 represents a novel regulator of early B cell development that exerts its function at a precise step in adult mice independently of other well-established regulators of B-cell development such as EBF or Pax5.

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Src homology 2 domain–containing inositol-5-phosphatase and CCAAT enhancer-binding protein β are targeted by miR-155 in B cells of Eμ-MiR-155 transgenic mice

Blood ◽

10.1182/blood-2009-05-220814 ◽

2009 ◽

Vol 114 (7) ◽

pp. 1374-1382 ◽

Cited By ~ 212

Author(s):

Stefan Costinean ◽

Sukhinder K. Sandhu ◽

Irene M. Pedersen ◽

Esmerina Tili ◽

Rossana Trotta ◽

...

Keyword(s):

Acute Lymphoblastic Leukemia ◽

B Cells ◽

Transgenic Mice ◽

B Cell ◽

Lymphoblastic Leukemia ◽

High Grade ◽

Src Homology 2 ◽

Enhancer Binding Protein ◽

Src Homology ◽

Src Homology 2 Domain

AbstractWe showed that Eμ-MiR-155 transgenic mice develop acute lymphoblastic leukemia/high-grade lymphoma. Most of these leukemias start at approximately 9 months irrespective of the mouse strain. They are preceded by a polyclonal pre–B-cell proliferation, have variable clinical presentation, are transplantable, and develop oligo/monoclonal expansion. In this study, we show that in these transgenic mice the B-cell precursors have the highest MiR-155 transgene expression and are at the origin of the leukemias. We determine that Src homology 2 domain–containing inositol-5-phosphatase (SHIP) and CCAAT enhancer-binding protein β (C/EBPβ), 2 important regulators of the interleukin-6 signaling pathway, are direct targets of MiR-155 and become gradually more down-regulated in the leukemic than in the preleukemic mice. We hypothesize that miR-155, by down-modulating Ship and C/EBPβ, initiates a chain of events that leads to the accumulation of large pre-B cells and acute lymphoblastic leukemia/high-grade lymphoma.

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Precursor B Cell Acute Lymphoblastic Leukemia Induces Pro-Leukemic Changes in the Bone Marrow Microenvironment That Contribute to Therapeutic Resistance

Blood ◽

10.1182/blood.v120.21.1466.1466 ◽

2012 ◽

Vol 120 (21) ◽

pp. 1466-1466

Author(s):

Christopher D Chien ◽

Elizabeth D Hicks ◽

Paul P Su ◽

Haiying Qin ◽

Terry J Fry

Keyword(s):

Bone Marrow ◽

Acute Lymphoblastic Leukemia ◽

B Cells ◽

B Cell ◽

Lymphoblastic Leukemia ◽

Cell Development ◽

B Cell Development ◽

Bone Marrow Microenvironment ◽

Therapeutic Resistance

Abstract Abstract 1466 Pediatric acute lymphoblastic leukemia (ALL) is the most common childhood malignancy. Although cure rates for this disease are approximately 90%, ALL remains one of the leading causes cancer-related deaths in children. Thus, new treatments are needed for those patients that do not respond to or recur following standard chemotherapy. Understanding the mechanisms underlying resistance of pediatric ALL to therapy offers one approach to improving outcomes. Recent studies have demonstrated the importance of communication between cancer cells and their microenvironment and how this contributes to the progression and therapeutic resistance but this has not been well studied in the context of ALL. Since the bone marrow is presumed to be the site of initiation of B precursor ALL we set out in our study to determine how ALL cells utilize the bone marrow milieu in a syngeneic transplantable model of preB cell ALL in immunocompetent mice. In this model, intravenously injected preB ALL develops first in the bone marrow, followed by infiltration into the spleen, lymph node, and liver. Using flow cytometry to detect the CD45.2 isoform following injection into B6CD45.1+ congenic recipients, leukemic cells can be identified in the bone marrow as early as 5 days after IV injection with a sensitivity of 0.01%-0.1%. The pre-B ALL line is B220+/CD19+/CD43+/BP1+/IL-7Ralpha (CD127)+/CD25-/Surface IgM-/cytoplasmic IgM+ consistent with a pre-pro B cell phenotype. We find that increasing amounts of leukemic infiltration in the bone marrow leads to an accumulation of non-malignant developing B cells at stages immediately prior to the pre-pro B cell (CD43+BP1-CD25-) and a reduction in non-malignant developing pre B cells at the developmental stage just after to the pre-pro B cell stage (CD43+BP1+CD25+). These data potentially suggest occupancy of normal B cell developmental niches by leukemia resulting in block in normal B cell development. Further supporting this hypothesis, we find significant reduction in early progression of ALL in aged (10–12 month old) mice known to have a deficiency in B cell developmental niches. We next explored whether specific factors that support normal B cell development can contribute to progression of precursor B cell leukemia. The normal B cell niche has only recently been characterized and the specific contribution of this niche to early ALL progression has not been extensively studied. Using a candidate approach, we examined the role of specific cytokines such as Interleukin-7 (IL-7) and thymic stromal lymphopoietin (TSLP) in early ALL progression. Our preB ALL line expresses high levels of IL-7Ralpha and low but detectable levels of TLSPR. In the presence of IL-7 (0.1 ng/ml) and TSLP (50 ng/ml) phosphSTAT5 is detectable indicating that these receptors are functional but that supraphysiologic levels of TSLP are required. Consistent with the importance of IL-7 in leukemia progression, preliminary data demonstrates reduced lethality of pr-B cell ALL in IL-7 deficient mice. Overexpression of TSLP receptor (TSLPR) has been associated with high rates of relapse and poor overall survival in precursor B cell ALL. We are currently generating a TSLPR overepressing preBALL line to determine the effect on early ALL progression and are using GFP-expressing preB ALL cells to identify the initial location of preB ALL occupancy in the bone marrow. In conclusion, or model of early ALL progression provides insight into the role of the bone marrow microenvironment in early ALL progression and provides an opportunity to examine how these microenvironmental factors contribute to therapeutic resistance. Given recent advances in immunotherapy for hematologic malignancies, the ability to study this in an immunocompetent host will be critical. Disclosures: No relevant conflicts of interest to declare.

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RNAi Screening Identifies A Novel Role for A-Kinase Anchoring Protein 12 (AKAP12) in B Cell Development and Function

Blood ◽

10.1182/blood.v120.21.855.855 ◽

2012 ◽

Vol 120 (21) ◽

pp. 855-855 ◽

Cited By ~ 1

Author(s):

Mutlu Kartal-Kaess ◽

Luisa Cimmino ◽

Simona Infantino ◽

Mehmet Yabas ◽

Jian-Guo Zhang ◽

...

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Leukemia Cell ◽

Cell Development ◽

B Cell Development ◽

Leukemia Cell Line ◽

B Lymphopoiesis ◽

Catalytic Subunits ◽

B Cell Leukemia

Abstract Abstract 855 The cAMP signaling pathway has emerged as a key regulator of hematopoietic cell proliferation, differentiation, and apoptosis. Signal specificity is achieved through local activation of signaling enzymes that are anchored to subcellular organelles and membranes. In particular, A-kinase anchoring proteins (AKAPs) coordinate and control cAMP responsive events. AKAPs were originally classified based on their ability to bind cAMP-dependent protein kinase (protein kinase A; PKA). The activity of PKA is regulated by its two regulatory subunits, which from a dimer that binds to the two catalytic subunits. Binding of cAMP to the regulatory dimer dissociates the catalytic subunits and activates PKA. Anchoring of PKA by AKAPs constrains PKA activity to a relevant subset of potential substrates. Thus, AKAPs contribute to the precision of intracellular signaling events by directing anchored enzyme pools to a subset of their physiological substrates at specific subcellular localizations. Using an in vitro short hairpin RNA (shRNA) screen against potentially druggable targets, we have uncovered a requirement for AKAP12 in the proliferation of a cultured pre-B cell leukemia cell line. In the hematopoietic system of mice and humans, expression of AKAP12 is tightly restricted to the pro/pre/immature stages of B lymphopoiesis, suggesting a potential role in pre-B cell receptor (pre-BCR) or BCR signaling. We find that retroviral knockdown or germline knockout of AKAP12 in mice leads to an increase in pre B and immature B cells in the bone marrow. In contrast, B cell numbers in the spleen are significantly reduced, as are recirculating B cells in the bone marrow. Transplantation of AKAP12 null hematopoietic stem and progenitor cells from fetal liver into wildtype recipients demonstrates an autonomous defect in the development of AKAP12−/− B cells. Competitive bone marrow transplantations confirm that this defect is cell autonomous and not due to a defective bone marrow environment or secretion of a B cell inhibitory factor. To identify AKAP12 interaction partners, we overexpressed FLAG-epitope tagged AKAP12 in a pre-B cell leukemia cell line. Affinity purification of AKAP12 showed a repeated co-immunoprecipitation of poorly characterized RIO kinase 1 (RIOK1). Our current efforts are focused on investigating the interaction between RIOK1 and AKAP12 and their role in the control of B cell development and cell cycle progression. Further, we are focusing on a likely role for AKAP12 in the scaffolding of PKA, PKC and phosphodiesterases by analyzing the activation of signaling cascades in cultured primary wildtype and AKAP12−/− pre B cells. Additionally, we are investigating the role of the BCR in vivo by testing if enforced expression of BCR components rescue B cell development in a AKAP12−/− BCR transgenic mouse model (SWHEL mouse). In summary, we have confirmed a novel role for AKAP12 in B lymphopoiesis. Disclosures: No relevant conflicts of interest to declare.

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B Cell Development in the Bone Marrow Is Regulated by Homeostatic Feedback Exerted by Mature B Cells

Frontiers in Immunology ◽

10.3389/fimmu.2016.00077 ◽

2016 ◽

Vol 7 ◽

Cited By ~ 9

Author(s):

Gitit Shahaf ◽

Simona Zisman-Rozen ◽

David Benhamou ◽

Doron Melamed ◽

Ramit Mehr

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Cell Development ◽

B Cell Development

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Regulated Expression of Human Histocompatibility Leukocyte Antigen (HLA)-DO During Antigen-dependent and Antigen-independent Phases of B Cell Development

Journal of Experimental Medicine ◽

10.1084/jem.20012066 ◽

2002 ◽

Vol 195 (8) ◽

pp. 1053-1062 ◽

Cited By ~ 47

Author(s):

Xinjian Chen ◽

Oskar Laur ◽

Taku Kambayashi ◽

Shiyong Li ◽

Robert A. Bray ◽

...

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Peripheral Blood ◽

Class Ii ◽

Cell Development ◽

B Cell Development ◽

Negative Regulator ◽

Leukocyte Antigen ◽

Peptide Loading

Human histocompatibility leukocyte antigen (HLA)-DO, a lysosomal resident major histocompatibility complex class II molecule expressed in B cells, has previously been shown to be a negative regulator of HLA-DM peptide loading function. We analyze the expression of DO in human peripheral blood, lymph node, tonsil, and bone marrow to determine if DO expression is modulated in the physiological setting. B cells, but not monocytes or monocyte-derived dendritic cells, are observed to express this protein. Preclearing experiments demonstrate that ∼50% of HLA-DM is bound to DO in peripheral blood B cells. HLA-DM and HLA-DR expression is demonstrated early in B cell development, beginning at the pro-B stage in adult human bone marrow. In contrast, DO expression is initiated only after B cell development is complete. In all situations, there is a striking correlation between intracellular DO expression and cell surface class II–associated invariant chain peptide expression, which suggests that DO substantially inhibits DM function in primary human B cells. We report that the expression of DO is markedly downmodulated in human germinal center B cells. Modulation of DO expression may provide a mechanism to regulate peptide loading activity and antigen presentation by B cells during the development of humoral immune responses.

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The Tetraspanin CD53 Regulates Early B Cell Development By Promoting IL-7R Signaling

Blood ◽

10.1182/blood-2019-131641 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 79-79

Author(s):

Zev J. Greenberg ◽

Darlene A. Monlish ◽

Rachel L. Bartnett ◽

Jeffrey J. Bednarski ◽

Laura G. Schuettpelz

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Conflicts Of Interest ◽

Cell Development ◽

B Cell Development ◽

Cellular Migration ◽

Physical Interaction ◽

Hematopoietic Stem ◽

Human Phenotype

The tetraspanin CD53 has been implicated in B cell development and function. Tetraspanins are a family of transmembrane proteins important for organization of the plasma membrane and regulation of cellular migration, adhesion, and activation. CD53 has been shown to be a transcriptional target of EBF1, a critical transcription factor for early B cell development. Additional signaling for early B cell development occurs through the IL-7 receptor (IL-7R), where ligation promotes continued B cell differentiation and pro-survival/anti-apoptotic gene expression. Human deficiency of CD53 results in recurrent infections and reduced serum immunoglobulins. While prior studies have implicated a role for CD53 in regulating mature B cells, its role in early B cell development is not well understood. Herein, we show that CD53 expression rapidly increases throughout B cell development, beginning at the pre-pro-B cell stage. With a CRISPR-generated knockout mouse, we show that Cd53-/- mice have significantly reduced bone marrow (25% fewer, p<0.005), splenic (35% fewer, p<0.05), lymphatic (65% fewer, p<0.0001), and peripheral (30% fewer, p<0.005) B cells compared to wild-type (WT) littermate controls. Mirroring the human phenotype, Cd53-/- mice have significantly reduced serum IgG and IgM (40% reduced, p<0.01). In addition, hematopoietic stem cells isolated from Cd53-/- mice give rise to 30% fewer B cells compared to controls in vitro (p=0.005). Analysis of bone marrow B cell development demonstrates that this loss of B cells originates with early B cell progenitors, which express nearly 50% less IL-7Ra than WT and reduced IL-7 signaling. Using mass cytometry, we identified differential signaling pathways downstream of IL-7R in B cell progenitors. Specifically, we observe impaired PI3K and STAT5 activation in pre-pro- and pro-B cells in the absence of CD53, with a consequent increase in apoptosis in these populations (p<0.01). Decreased STAT5 phosphorylation was confirmed by western blot. Finally, co-immunoprecipitation studies demonstrate a physical interaction between CD53 and IL-7Ra, suggesting that these proteins associate at the cell surface. Together, these data suggest a novel role for CD53 during IL-7 signaling to promote early B cell development. Ongoing studies are focused on determining the CD53 residues required for interaction with IL-7R. Disclosures No relevant conflicts of interest to declare.

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Chronic GvHD Is Characterized By Impaired B Cell Development in the Bone Marrow

Blood ◽

10.1182/blood.v126.23.1883.1883 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1883-1883

Author(s):

Oleg Kolupaev ◽

Michelle West ◽

Bruce R. Blazar ◽

Stephen Tilley ◽

James Coghill ◽

...

Keyword(s):

Bone Marrow ◽

T Cells ◽

B Cells ◽

B Cell ◽

Cd4 T Cells ◽

Critical Role ◽

Cell Development ◽

B Cell Development ◽

B Lymphopoiesis

Abstract Background. Chronic-graft-versus-host disease (cGvHD) continues to be a major complication following allogeneic hematopoietic stem cell transplantation (HSCT). Despite significant progress, mechanisms underlying development of the pathology are yet to be fully understood. Recent studies utilizing mouse models and patient samples have demonstrated a critical role for B cells in GvHD pathogenesis. Bone marrow (BM)-derived B cells can produce auto-reactive antibodies causing tissue fibrosis and multiorgan cGvHD. Impaired B cell homeostasis in the periphery, activation due to abnormally high levels of B cell-activating factor (BAFF), increased survival of auto-reactive B cells and aberrant BCR signaling are shown to be important for disease progression in cGvHD patients. Murine models also highlighted the critical role of germinal center reactions, particularly interactions between T follicular helper (Tfh) cells and B cells for generation of auto-antibodies which are responsible for triggering immune responses and cell-mediated toxicity. A growing body of evidence has emerged highlighting the fact that BM itself is a target organ during acute GvHD (aGvHD) with recent work suggesting a role for donor CD4+ T cells in BM specific aGvHD. Our group has shown that patients with higher numbers of BM B cell precursors were less likely to develop cGvHD after allogeneic HSCT (Fedoriw et al., 2012). These observations indicate clinical relevance of impaired BM B lymphopoiesis for cGvHD development. Methods. In order to investigate the effect of cGvHD on BM B cell development, we used the well-characterized major mismatch B6 into B10.BR model of systemic cGvHD. Recipient mice were treated with cyclophosphamide on day -3 and -2, irradiated with 700 cGy on day -1, and injected with 107 T cell depleted (TCD) BM with or without total splenic T cells (0.5-1x105). Mice were monitored for 30 days, and BM and spleen was harvested and analyzed using flow cytometry. Results. Consistent with patient data, we observed a decrease in the frequency and number of donor-derived uncommitted common lymphoid progenitors (CLP) and B cell progenitors in the BM+ allogeneic T cells group (CLP: 0.17±0.03% vs. 0.06±0.01%, p <0.01; pro B: 2.2 ± 0.5% vs. 0.7 ± 0.3%, p<0.05; pre B: 15.3±1.8% vs. 6.3±2.4%, p<0.05; immature B cells: 5.7±0.7% vs. 2.1±0.7%, p<0.01) (Fig.1). As previously reported for this model, we also found a decrease in the frequency of follicular (FO) B cells (Flynn et al., 2014). We hypothesized that during cGvHD the B cell progenitor BM niche is affected by donor CD4+ T cells leading to impaired B lymphopoiesis. Bone marrow from BM+T cell animals had a significantly higher frequency of CD4+ cells compared to the control group (0.45±0.06% vs. 0.2±0.02%). Depletion of CD4+ T cells using anti-CD4 antibody during the first two weeks after transplant improved pathology scores and prevented weight loss in BM+T cells mice. We also observedpartial recovery of B cell progenitors and Lin-CD45-CD31-CD51+ osteoblasts (OB) in animals treated with anti-CD4 antibodies (pre B 3.5±1.1% vs. 20.4±4.5%, p<0.05; immature B: 1.9±0.9% vs. 3.5±0.3%; OB: 0.8±0.1% vs.1.2±0.2%). A recent study showed that activation and proliferation of conventional T cells in aGvHD model can be prevented by in vivo expansion of regulatory T cells (Tregs) using αDR3 antibody (4C12). We adopted this approach to determine whether Tregs can suppress the cytotoxic effect of donor CD4+ T cells in BM in cGvHD model. Animals that received T cells from 4C12-treated donors had an increase in survival and lower cGvHD pathology scores. These mice also had higher frequency of pro B, pre B, and immature B cells compared to the mice infused with T cells from isotype-treated donors. Conclusions. These studies demonstrate that BM development of B lymphocytes is impaired in a mouse model of systemic cGvHD. Our data suggests that donor-derived CD4+ T cells are involved in the destruction of hematopoietic niches in BM, particularly OB, which support B lymphopoiesis. Moreover, depletion of CD4+ T cells and infusion with in vivo expanded Tregs reduced the severity of cGvHD. Thus, Treg therapy in patients with cGvHD may be important for BM B cell development, and improvement of clinical outcomes. Disclosures No relevant conflicts of interest to declare.

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The mitochondrial iron transporter ABCB7 is required for B cell development, proliferation, and class switch recombination in mice

eLife ◽

10.7554/elife.69621 ◽

2021 ◽

Vol 10 ◽

Author(s):

Michael Jonathan Lehrke ◽

Michael Jeremy Shapiro ◽

Matthew J Rajcula ◽

Madeleine M Kennedy ◽

Shaylene A McCue ◽

...

Keyword(s):

Bone Marrow ◽

B Cells ◽

B Cell ◽

Class Switch Recombination ◽

Cell Development ◽

B Cell Development ◽

Intracellular Iron ◽

Cell Stage ◽

Class Switch ◽

Mitochondrial Transporter

Iron-sulfur (Fe-S) clusters are cofactors essential for the activity of numerous enzymes including DNA polymerases, helicases, and glycosylases. They are synthesized in the mitochondria as Fe-S intermediates and are exported to the cytoplasm for maturation by the mitochondrial transporter ABCB7. Here, we demonstrate that ABCB7 is required for bone marrow B cell development, proliferation, and class switch recombination, but is dispensable for peripheral B cell homeostasis in mice. Conditional deletion of ABCB7 using Mb1-cre resulted in a severe block in bone marrow B cell development at the pro-B cell stage. The loss of ABCB7 did not alter expression of transcription factors required for B cell specification or commitment. While increased intracellular iron was observed in ABCB7-deficient pro-B cells, this did not lead to increased cellular or mitochondrial reactive oxygen species, ferroptosis, or apoptosis. Interestingly, loss of ABCB7 led to replication-induced DNA damage in pro-B cells, independent of VDJ recombination, and these cells had evidence of slowed DNA replication. Stimulated ABCB7-deficient splenic B cells from CD23-cre mice also had a striking loss of proliferation and a defect in class switching. Thus, ABCB7 is essential for early B cell development, proliferation, and class switch recombination.

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