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

Blood ◽  
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.

scholarly journals Interactions Between c-kit and Stem Cell Factor Are Not Required for B-Cell Development In Vivo

Blood ◽  
1997 ◽  
Vol 89 (2) ◽  
pp. 518-525 ◽  
Author(s):  
Shunichi Takeda ◽  
Takeyuki Shimizu ◽  
Hans-Reimer Rodewald
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Fetal Liver ◽  
Critical Role ◽  
Cell Development ◽  
B Cell Development ◽  
Wild Type ◽  
Hematopoietic Stem

Abstract The receptor-type tyrosine kinase, c-kit is expressed in hematopoietic stem cells (HSC), myeloid, and lymphoid precursors. In c-kit ligand-deficient mice, absolute numbers of HSC are mildly reduced suggesting that c-kit is not essential for HSC development. However, c-kit− HSC cannot form spleen colonies or reconstitute hematopoietic functions in lethally irradiated recipient mice. Based on in in vitro experiments, a critical role of c-kit in B-cell development was suggested. Here we have investigated the B-cell development of c-kitnull mutant (W/W ) mice in vivo. Furthermore, day 13 fetal liver cells from wild type or W/W mice were transferred into immunodeficient RAG-2−/− mice. Surprisingly, transferred c-kit− cells gave rise to all stages of immature B cells in the bone marrow and subsequently to mature conventional B2, as well as B1, type B cells in the recipients to the same extent as transferred wild type cells. Hence, in contrast to important roles of c-kit in the expansion of HSC and the generation of erythroid and myeloid lineages and T-cell precursors, c-kit− HSC can colonize the recipient bone marrow and differentiate into B cells in the absence of c-kit.

scholarly journals Ligand-independent Signaling Functions for the B Lymphocyte Antigen Receptor and Their Role in Positive Selection during B Lymphopoiesis

2001 ◽  
Vol 194 (11) ◽  
pp. 1583-1596 ◽  
Author(s):  
Gregory Bannish ◽  
Ezequiel M. Fuentes-Pananá ◽  
John C. Cambier ◽  
Warren S. Pear ◽  
John G. Monroe
Keyword(s):  
B Cells ◽  
B Cell ◽  
B Lymphocyte ◽  
Antigen Receptor ◽  
Cell Development ◽  
B Cell Development ◽  
B Lymphopoiesis ◽  
Biologically Relevant ◽  
Developmental Progression

Signal transduction through the B cell antigen receptor (BCR) is determined by a balance of positive and negative regulators. This balance is shifted by aggregation that results from binding to extracellular ligand. Aggregation of the BCR is necessary for eliciting negative selection or activation by BCR-expressing B cells. However, ligand-independent signaling through intermediate and mature forms of the BCR has been postulated to regulate B cell development and peripheral homeostasis. To address the importance of ligand-independent BCR signaling functions and their regulation during B cell development, we have designed a model that allows us to isolate the basal signaling functions of immunoglobulin (Ig)α/Igβ-containing BCR complexes from those that are dependent upon ligand-mediated aggregation. In vivo, we find that basal signaling is sufficient to facilitate pro-B → pre-B cell transition and to generate immature/mature peripheral B cells. The ability to generate basal signals and to drive developmental progression were both dependent on plasma membrane association of Igα/Igβ complexes and intact immunoregulatory tyrosine activation motifs (ITAM), thereby establishing a correlation between these processes. We believe that these studies are the first to directly demonstrate biologically relevant basal signaling through the BCR where the ability to interact with both conventional as well as nonconventional extracellular ligands is eliminated.

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

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 855-855 ◽  
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.

Gene Targeting of RhoA Reveals Its Essential Role In Lymphopoiesis

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 282-282
Author(s):  
Shuangmin Zhang ◽  
Yi Zheng ◽  
Richard Lang ◽  
Fukun Guo
Keyword(s):  
T Cells ◽  
T Cell ◽  
B Cells ◽  
B Cell ◽  
Cell Development ◽  
B Cell Development ◽  
Brdu Incorporation ◽  
Hematopoietic Stem ◽  
Cell Functions

Abstract Abstract 282 RhoA GTPase is an intracellular signal transducer capable of regulating a wide range of cell functions including cytoskeleton dynamics, proliferation, and survival. In lymphocytes, studies by using dominant negative mutant or C3 transferase expressing transgenic mice suggest that RhoA is involved in TCR and BCR signaling and related T cell functions such as polarization, migration, survival, and proliferation. To date, the physiological role of RhoA in lymphocyte development remains unclear. In this study, we have achieved T cell, B cell, and hematopoietic stem cell-specific deletion of RhoA by conditional gene targeting with CD2, CD19 and Mx1 promoter-driven Cre expression, respectively, in the RhoAloxP/loxP mice. First, we found that RhoA gene disruption in early T cells caused a drastic decrease in thymocyte cellularity, with the numbers of CD4−CD8− double negative (DN), CD4+CD8+ double positive (DP), CD4+CD8− single positive (SP), and CD4−CD8+ SP T cells decreased by 88.8% ± 6.0%, 99.4% ± 1.0%, 99.3% ± 1.2%, and 98.6% ± 2.0%, respectively. Among DN subpopulations, CD44+CD25− (DN1), CD44+CD25+ (DN2), CD44−CD25+ (DN3), and CD44−CD25− (DN4) cells were reduced by 91.7% ± 6.0%, 54.9% ± 27.7%, 50.9% ± 33.3%, and 96.7% ± 3.4%, respectively. Further, RhoA knockout led to a significant loss of DP thymocytes at the initial stage (CD69highTCRint) of positive selection, suggesting that RhoA is required for positive selection. The decreased thymocyte cellularity in mutant mice is associated with increased apoptosis of all thymic T lineages. RhoA deficiency also resulted in a perturbation in thymocyte cell cycle progression as manifested by increased BrdU incorporation in DN1 and DN2 cells and decreased BrdU incorporation in DN4 and DP cells. Concomitantly, RhoA-deficient thymocytes showed a 59.8% ± 26.3% reduction in proliferative potential in response to TCR crosslinking. Western blot analysis revealed that the activities of ZAP70, LAT, Akt, Erk, and p38 were impaired in RhoA-/- thymocytes. In periphery, spleens of the RhoA null mice contained 7.4% ± 8.0% of CD4+ T cells and 3.7% ± 2.7% of CD8+ T cells compared with that of wild type (WT) mice. Loss of peripheral mature T cells in mutant mice is reflected by a marked reduction of naive T cells, whereas effector and memory phenotype cells were marginally affected by RhoA deficiency. RhoA-deficient naïve T cells were more susceptible to apoptosis, suggesting that homeostatic defect of naïve T cells in RhoA-/- mice is attributed to impaired cell survival. Abrogation of RhoA caused an increased in vivo BrdU incorporation in naïve T cell compartments. Thus, RhoA deficiency induces naïve T cell homeostatic proliferation, possibly due to a compensatory effect of lymphopenia. In contrast to that in thymocytes, Erk was constitutively activated in RhoA-deficient splenic T cells. These observations implicate RhoA in the multiple stages of T cell development and the proper assembly of early TCR signaling complex. Second, deletion of RhoA in pre-proB cells had no effect on early B cell development in bone marrow but significantly inhibited late B cell development in spleen, resulting in 78.2% ± 13.6%, 78.6% ± 16.9%, and 93.2% ± 3.4% reduction in transitional, follicular, and marginal zone B cells, respectively. Plasma cells in spleen were decreased by 50.9 % ± 25.9% in RhoA null mice. However, we did not detect any changes in survival of in vivo RhoA-/- B cells or RhoA-/- B cells cultured in vitro with survival factor BAFF. Distinct from previously characterized Cdc42 knockout mice, BAFF-R expression was not altered in RhoA-/- B cells. Moreover, RhoA-/- B cells appeared to be normal in proliferation and Akt and Erk activation in response to BCR crosslinking. These data suggest that RhoA is important for late B cell development through regulation of differentiation but not cell survival or proliferation. Finally, deletion of RhoA from hematopoietic stem cells did not affect common lymphoid progenitor production, indicating that RhoA is not required for early lymphoid progenitor commitment. Taken together, these lineage-specific mouse genetic studies demonstrate that RhoA critically regulates T and B cell development by distinct cellular mechanisms at multiple stages of lymphopoiesis. Disclosures: No relevant conflicts of interest to declare.

G-CSF-Induced Alterations in the Bone Marrow Microenvironment Suppress B Lymphopoiesis

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1246-1246
Author(s):  
Ryan B. Day ◽  
Adam Greenbaum ◽  
Daniel C. Link
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Stromal Cells ◽  
Cell Development ◽  
B Cell Development ◽  
Bone Marrow Microenvironment ◽  
B Lymphopoiesis ◽  
Treatment Results ◽  
Cell Suppression

Abstract Abstract 1246 Infectious stress is associated with a shift in the bone marrow from lymphopoiesis to granulopoiesis. Expression of granulocyte colony-stimulating factor (G-CSF), the principal cytokine regulating granulopoiesis, is often induced during infection. We previously reported that G-CSF treatment is associated with marked suppression of B lymphopoiesis in murine bone marrow. After 5 days of G-CSF treatment (250 μg/kg), total B cells in the bone marrow were reduced 8.1 ± 0.9-fold. Pre-pro-B cells were reduced 1.6 ± 0.3-fold, pro-B cells 12.4 ± 1.9-fold, pre-B cells 5.6 ± 0.8-fold, immature B cells 7.5 ± 1.2-fold, and mature naïve B cells 83 ± 7.6-fold. B-committed lymphoid progenitors (BLP) were modestly but significantly decreased (1.4 ± 0.2-fold), while common lymphoid progenitors (CLP) were not affected by G-CSF treatment. Increased apoptosis of mature naïve B cells in the bone marrow was observed. Studies of G-CSF receptor deficient (Csf3r−/−) bone marrow chimeras show that G-CSF acts in a non-cell intrinsic fashion to suppress B lymphopoiesis. Consistent with this observation, we show that G-CSF treatment results in decreased expression in the bone marrow microenvironment of multiple B-supportive factors including CXCL12, interleukin-6, interleukin-7, and B cell activating factor (BAFF). Prior studies have established that CXCL12-abundant reticular (CAR) cells in the bone marrow play a key role in B cell development. CAR cells are perivascular stromal cells that express very high levels of CXCL12 and are in direct contact with pre-pro-B cells. G-CSF treatment did not affect CAR cell number. However, RNA expression profiling of sorted CAR cells showed that expression of several genes associated with B cell development are significantly decreased by G-CSF, including CXCL12 (4.2 ± 1.5-fold). In addition to CAR cells, other stromal cells in the bone marrow express CXCL12, including osteoblasts and endothelial cells. To assess the role of CXCL12 production by each of these cell types to B lymphopoiesis, we generated Cxcl12flox mice and crossed them with mice expressing the following tissue-specific Cre-recombinase transgenes: Osteocalcin-Cre (Oc-Cre) targeting mature mineralizing osteoblasts; Osterix-Cre (Osx-Cre) targeting CAR cells and all osteolineage cells; or Prx1-Cre targeting mesenchymal progenitors and their progeny. Deletion of Cxcl12 using Oc-Cre or Osx-Cre had a similar effect on B cell development, with an isolated loss of mature naïve B cells in the bone marrow (2.7 ± 0.5 and 4.1 ± 1.7-fold, respectively). In contrast, deletion of Cxcl12 using Prx1-Cre resulted in severe suppression of B lymphopoiesis that included a loss of CLP (3.3 ± 2.0-fold), BLP (5.6 ± 4.3-fold), and pre-pro-B cells (12.4 ± 5.1-fold). Interestingly, treatment of Prx1-Cre Cxcl12flox/- mice with G-CSF resulted in additional B cell loss, indicating that deletion of Cxcl12 in mesenchymal stromal cells is not sufficient to fully recapitulate G-CSF-induced B cell suppression. In summary, G-CSF treatment results in marked changes in the bone marrow microenvironment that lead to a suppression of B lymphopoiesis. While G-CSF-induced inhibition of CXCL12 expression from stromal cells contributes to B cell suppression, additional alterations in the microenvironment also contribute to this phenotype. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Impaired bone marrow B-cell development in mice with a bronchiolitis obliterans model of cGVHD

2018 ◽  
Vol 2 (18) ◽  
pp. 2307-2319 ◽  
Author(s):  
Oleg V. Kolupaev ◽  
Trisha A. Dant ◽  
Hemamalini Bommiasamy ◽  
Danny W. Bruce ◽  
Kenneth A. Fowler ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
B Cell ◽  
Bronchiolitis Obliterans ◽  
Critical Role ◽  
Cell Development ◽  
B Cell Development ◽  
Allogeneic Bone ◽  
B Cell Precursors

Abstract Chronic graft-versus-host disease (cGVHD) causes significant morbidity and mortality in patients after allogeneic bone marrow (BM) or stem cell transplantation (allo-SCT). Recent work has indicated that both T and B lymphocytes play an important role in the pathophysiology of cGVHD. Previously, our group showed a critical role for the germinal center response in the function of B cells using a bronchiolitis obliterans (BO) model of cGVHD. Here, we demonstrated for the first time that cGVHD is associated with severe defects in the generation of BM B lymphoid and uncommitted common lymphoid progenitor cells. We found an increase in the number of donor CD4+ T cells in the BM of mice with cGVHD that was negatively correlated with B-cell development and the frequency of osteoblasts and Prrx-1–expressing perivascular stromal cells, which are present in the B-cell niche. Use of anti-DR3 monoclonal antibodies to enhance the number of donor regulatory T cells (Tregs) in the donor T-cell inoculum ameliorated the pathology associated with BO in this model. This correlated with an increased number of endosteal osteoblastic cells and significantly improved the generation of B-cell precursors in the BM after allo-SCT. Our work indicates that donor Tregs play a critical role in preserving the generation of B-cell precursors in the BM after allo-SCT. Approaches to enhance the number and/or function of donor Tregs that do not enhance conventional T-cell activity may be important to decrease the incidence and severity of cGVHD in part through normal B-cell lymphopoiesis.

LRF Critically Regulates Mature B Cell Fate and Germinal Center Response Via Notch-Dependent and -Independent Mechanisms.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1961-1961
Author(s):  
Nagisa Sakurai ◽  
Manami Maeda ◽  
Sung-UK Lee ◽  
Toshiki Saito ◽  
Shigeru Chiba ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Fate ◽  
Knockout Mice ◽  
Critical Role ◽  
Notch Pathway ◽  
Cell Development ◽  
B Cell Development ◽  
Secondary Lymphoid Organs

Abstract Abstract 1961 Poster Board I-984 LRF (Leukemia/Lymphoma Related Factor) is a transcriptional repressor originally identified as an interaction partner of the oncoprotein BCL6 (B cell Lymphoma 6). We previously found that LRF acts as a proto-oncogene by repressing tumor suppressor ARF (Alternative Reading Frame, also known as p19 in mice and p14 in humans) and is highly expressed in 60-80% of human Non-Hodgkin Lymphoma (NHL) cases (Maeda et al., Nature 2005). LRF was also found to be indispensable for hematopoietic stem cells (HSCs) to commit to the B cell lineage by opposing Notch function (Maeda et al., Science 2007). Considering that: 1) LRF is normally expressed in Germinal Center B cells (GCB) and overexpressed in NHL tissues and 2) LRF opposes Notch function to maintain normal B cell fate at HSC/progenitor levels, we explored the role of LRF in B cell development and its functional interaction with the Notch pathway in vivo. Upon T cell dependent (TD) immunization, GC formation was severely impaired in secondary lymphoid organs of B cell specific LRF conditional knockout mice (LRFflox/flox mb1-Cre+). While a GC reaction was robustly induced in control mice upon immunization, only few GCB cells were noted in secondary lymphoid organs of LRFflox/flox mb1-Cre+ mice. To assess functional significance of LRF loss in antigen response in vivo, titers of class-switched immunoglobulin (Ig) were measured in the serum; baseline serum titers of IgG1, IgG2b and IgG3 were perturbed, and the primary and secondary antibody response against the TD antigen was impaired in LRFflox/flox mb1-Cre+ mice. Absolute numbers of memory B cells and long-lived BM plasma cells were reduced in LRFflox/flox mb1-Cre+ mice 20 wk after immunization. To determine the cause of defective GC formation, apoptosis and proliferation of GCB cells were examined by FACS. While proportions of apoptotic (AnnexinV positive) GCB cells were similar, regardless of genotypes, LRF deficient GCB cells failed to proliferate upon antigen stimuli. Short-term kinetic analysis demonstrated 5-ethynyl-2'-deoxyuridine (EdU) incorporation was markedly decreased in LRF deficient GCB cells and that the proportion of GCB cells in S phase was reduced in LRFflox/flox mb1-Cre+ mice. In agreement with these findings, quantitative RT-PCR analysis in FACS-sorted GCB cells demonstrated up-regulation of p19Arf and p21, but not p53, mRNA levels in LRF deficient GCB cells. Up-regulation of p19Arf protein levels was also observed in Western Blots. Furthermore, microarray analysis and subsequent Gene Set Enrichment Analysis in FACS-sorted GCB cells showed signatures of defective proliferation, further implicating a critical role for LRF in GCB cell proliferation. Signals mediated by Notch2 are necessary for transitional B cells to commit to the marginal zone B cells (MZB). Inactivation of a component of the Notch pathway in mice resulted in no MZB development and increased follicular B cells (FOB). On the contrary, deletion of the MINT/SHARP gene, a suppressor of Notch signaling, lead to increase of MZB cells and concomitant reduction of FOB cells, indicating that Notch induces MZB cell fate at the transitional B cell stage. While B cell development in the BM was grossly normal, a reduction of FOB cells and a concomitant increase of MZB cells were observed in LRFflox/flox mb1-Cre+ mice. Since the phenotype was reminiscent of that seen in MINT/SHARP knockout mice and opposite to that observed in Notch2 knockout mice, we hypothesized that LRF antagonizes Notch2 mediated signal during the FOB vs. MZB fate determination process. To test this, LRF/Notch2 double knockout mice (LRFflox/flox Notch2flox/flox mb1-Cre+) were established and their mature B cell compartments analyzed. As expected, loss of the Notch2 gene led to an increase of FOB cells and decrease of MZB in LRFflox/flox mb1-Cre+ mice, suggesting that LRF regulates FOB vs. MZB fate in a Notch2 dependent manner. However, Notch2 deficiency did not restore GC formation in LRFflox/flox mb1-Cre+ mice. In summary, our genetic studies strongly indicate that the proto-oncogene LRF is required for normal mature B cell development and function via distinct mechanisms. We propose that LRF is necessary for mature B cell fate by blocking Notch2-mediated signals and plays a critical role in GCB cell proliferation via suppressing p19Arf mediated cell cycle arrests. Our findings provide a further rational for targeting LRF for the treatment of B cell malignancies as well as autoimmune diseases. Disclosures: No relevant conflicts of interest to declare.

G-CSF Induces Alterations in the Bone Marrow Microenvironment That Suppress B Lymphopoiesis,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3243-3243
Author(s):  
Ryan B Day ◽  
Adam Greenbaum ◽  
Mahil Rao ◽  
Daniel Link
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Cell Development ◽  
B Cell Development ◽  
Bone Marrow Microenvironment ◽  
B Lymphopoiesis ◽  
Wild Type ◽  
Treatment Results ◽  
A Cell

Abstract Abstract 3243 During infectious stress, there is a marked shift in the bone marrow from lymphopoiesis to granulopoiesis. Granulocyte colony-stimulating factor (G-CSF) is the principal cytokine regulating granulopoiesis, and its expression is induced during infection. In this study, we show that G-CSF treatment in mice is associated with a marked suppression of lymphopoiesis in the bone marrow. Specifically, after 5 days of G-CSF treatment (250 μg/kg), the number of B cells in the bone marrow was reduced 8.6 ± 1.3-fold, the number of T cells reduced 14.8 ± 3.8-fold, and the number of NK cells reduced 7.5 ± 1.6-fold. Though modest increases in splenic and blood lymphocytes were observed following G-CSF treatment, this did not account for the loss in the bone marrow. To assess B cell development, modified Hardy fractions were analyzed. All stages of B cell development were significantly reduced by G-CSF, but to different degrees. Fraction A (pre-pro B cells) declined 2.1 ± 0.5-fold; fraction B/C (mostly pro-B cells): 9.4 ± 1.7-fold; fraction D cells (pre-B cells): 5.9 ±1.1-fold; fraction E (immature B cells): 8.1 ± 1.6-fold; and fraction F (mature B cells): 87 ±13-fold. In addition, mature plasma cells declined 1.3 ± 0.07-fold while immature plasmablasts decreased 7.7 ± 1.7-fold. Interestingly, preliminary analysis suggests that there is no significant change in the number of common lymphoid progenitors in the bone marrow. Since there are reports of G-CSF receptor (G-CSFR) expression on certain B cell subsets, we next asked whether G-CSFR signals act in a cell-intrinsic fashion to suppress B lymphopoiesis. Mixed bone marrow chimeras were generated that contain both wild type and G-CSFR−/− bone marrow cells. G-CSF treatment of these mixed chimeras demonstrated equal suppression of wild type and G-CSFR−/− B cells. Thus, G-CSF works in a cell-extrinsic fashion to suppress B lymphopoiesis. Certain bone marrow stromal cell populations are known to regulate B lymphopoiesis, including osteoblasts and CXCL12-abundant reticular (CAR) cells. We previously showed that G-CSF treatment results in a loss of mature osteoblasts. To examine CAR cells, we analyzed mice in which green fluorescent protein (GFP) has been knocked-in to the Cxcl12 locus, allowing for CAR cell identification (Tokoyoda et al. 2004). Whereas G-CSF treatment did not alter the number of CAR cells, a significant decrease in GFP expression per CAR cell was observed. Consistent with this observation, we observed a significant decrease in CXCL12 mRNA expression in the bone marrow following G-CSF treatment. Interestingly, we also noted significant decreases in RNA and/or protein expression of a number of B-supportive cytokines, including interleukin-6, interleukin-7, and B cell activating factor (BAFF) protein. In summary, G-CSF treatment results in marked changes in the bone marrow microenvironment that lead to a suppression of B lymphopoiesis. The ability of G-CSF to disrupt homeostatic signals required for B cell maintenance at multiple stages of development suggest that upfront G-CSF treatment may be a novel strategy to sensitize certain B cell malignancies to chemotherapy. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Lymphopenia in interleukin (IL)-7 gene-deleted mice identifies IL-7 as a nonredundant cytokine.

1995 ◽  
Vol 181 (4) ◽  
pp. 1519-1526 ◽  
Author(s):  
U von Freeden-Jeffry ◽  
P Vieira ◽  
L A Lucian ◽  
T McNeil ◽  
S E Burdach ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
B Cells ◽  
B Cell ◽  
Gene Targeting ◽  
B Cell Development ◽  
B Lymphopoiesis ◽  
T And B Cells ◽  
Immature B Cells ◽  
Deficient Mice

Interleukin (IL)-7 is a potent stimulus for immature T and B cells and, to a lesser extent, mature T cells. We have inactivated the IL-7 gene in the mouse germline by using gene-targeting techniques to further understand the biology of IL-7. Mutant mice were highly lymphopenic in the peripheral blood and lymphoid organs. Bone marrow B lymphopoiesis was blocked at the transition from pro-B to pre-B cells. Thymic cellularity was reduced 20-fold, but retained normal distribution of CD4 and CD8. Splenic T cellularity was reduced 10-fold. Splenic B cells, also reduced in number, showed an abnormal population of immature B cells in adult animals. The remaining splenic populations of lymphocytes showed normal responsiveness to mitogenic stimuli. These data show that proper T and B cell development is dependent on IL-7. The IL-7-deficient mice are the first example of single cytokine-deficient mice that exhibit severe lymphoid abnormalities.

scholarly journals Differential Regulation of Mouse B Cell Development by Transforming Growth Factor β1

2002 ◽  
Vol 9 (2) ◽  
pp. 86-95 ◽  
Author(s):  
Denise A. Kaminski ◽  
John J. Letterio ◽  
Peter D. Burrows
Keyword(s):  
B Cells ◽  
Growth Factor ◽  
B Cell ◽  
Transforming Growth Factor ◽  
Plasma Cells ◽  
Population Analysis ◽  
Cell Development ◽  
B Cell Development

Transforming growth factor β (TGFβ) can inhibit thein vitroproliferation, survival and differentiation of B cell progenitors, mature B lymphocytes and plasma cells. Here we demonstrate unexpected, age-dependent reductions in the bone marrow (BM) B cell progenitors and immature B cells in TGFβ1-/-mice. To evaluate TGFβ responsiveness during normal B lineage development, cells were cultured in interleukin 7 (IL7)±TGFβ. Picomolar doses of TGFβ1 reduced pro-B cell recoveries at every timepoint. By contrast, the pre-B cells were initially reduced in number, but subsequently increased compared to IL7 alone, resulting in a 4-fold increase in the growth rate for the pre-B cell population. Analysis of purified BM sub-populations indicated that pro-B cells and the earliest BP1-pre-B cells were sensitive to the inhibitory effects of TGFβ1. However, the large BP1+pre-B cells, although initially reduced, were increased in number at days 5 and 7 of culture. These results indicate that TGFβ1 is important for normal B cell developmentin vivo, and that B cell progenitors are differentially affected by the cytokine according to their stage of differentiation.

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