scholarly journals CYT-0853, a Novel RAD51 Inhibitor, Modulates Immunoregulatory B-Lymphocytes

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 2330-2330
Author(s):  
Tamar Aprahamian ◽  
ED Keniston ◽  
Jane Branca ◽  
Muneer G Hasham ◽  
Melinda Day ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Antibody Production ◽  
Cytidine Deaminase ◽  
Autoreactive B Cells ◽  
Freund’S Adjuvant ◽  
Freund's Adjuvant

Activation Induced Cytidine Deaminase (AICDA/AID) is a DNA-directed cytidine deaminase that is normally only expressed in activated B-cells to promote somatic hypermutations and immunoglobulin class switching. In cancer cells, AID causes significant genotoxic stress through DNA replication fork damage, creating a dependency upon the homologous recombination repair factor, RAD51, for survival. We have demonstrated anti-cancer activity through disruption of this axis in multiple preclinical lymphoid cancer models. Autoreactive B cells depend on RAD51 for survival and are chronically auto-stimulated and therefore continually re-express AID. It has been shown that ectopic expression of AID in autoreactive B-cells causes genome-wide DNA damage (similar to cancers). Given the role of autoreactive B cells and autoantibodies in autoimmune disorders, we hypothesize that immunomodulation of B cells via the RAD51/AID axis will remediate inflammatory disease processes. Our previous data suggests that RAD51 modulation enhances the CD73+ B cell population and reduces antibody diversity in T1D mice, indicating precise effects on AID-mediated antibody diversification. CYT-0853 is a novel RAD51 inhibitor that sensitizes cells to AID activity. Here, we assessed the in vivo effect of CYT-0853 on primary B cells and antibody production. Wild-type C57BL/6 mice were treated with 40mg/kg CYT-0853 or vehicle for five weeks. One-week post-treatment start, mice were immunized with DNP-KLH antigen mixed with Complete Freund's Adjuvant. A second booster with DNP-KLH antigen mixed with Incomplete Freund's Adjuvant was administered two weeks later. At termination, blood, spleen, and bone marrow was collected for analysis by flow cytometry. Surface expression of CD45, CD19, IgM, and IgG1 was assessed to determine white blood cell count, B cells, and pre- and post-class switch recombination (CSR), respectively. While no significant changes to B cell populations were observed in bone marrow or spleen, we demonstrate that CYT-0853 significantly decreases the median number of circulating CD45+ and IgG1 (post-CSR) B cells (61.8% vs. 31.6% and 8.7% vs. 4.4%, respectively). In addition, we observed a modest, significant increase in the amount of IgM+ (pre-CSR) B cells. These results were complemented by an associated overall significant decrease in circulating IgM levels. Of note, no adverse effects were observed in these mice over this treatment period. Based on these data and the role of B cells not only in antibody production, but also as antigen-presenting cells in multiple sclerosis, we tested our molecule in the myelin oligodendrocyte glycoprotein35-55-experimental autoimmune encephalomyelitis model of multiple sclerosis. Prophylactic treatment using 40mg/kg CYT-0853 did not affect disease activity or circulating cytokine production, however we observed a significant decrease in the spleen. Based on these results, further exploration is warranted to harness the power of CYT-0853 on the AID/RAD51 axis. This specific targeting may elicit beneficial therapeutic changes to B-lymphocyte populations and provide a novel immunomodulatory target to treat immunity and inflammation. Taken together, these data provide a foundation for continued preclinical development of CYT-0853 with applicability towards autoimmune diseases. Disclosures Aprahamian: Cyteir Therapeutics: Consultancy. Day:Cyteir Therapeutics: Employment. Mills:Cyteir Therapeutics: Employment, Equity Ownership.

Bruton's tyrosine kinase inhibition in the treatment of preclinical models and multiple sclerosis

2021 ◽  
Vol 27 ◽  
Author(s):  
Anja Steinmaurer ◽  
Isabella Wimmer ◽  
Thomas Berger ◽  
Paulus Stefan Rommer ◽  
Johann Sellner
Keyword(s):  
Multiple Sclerosis ◽  
B Cells ◽  
Tyrosine Kinase ◽  
B Cell ◽  
Bruton’S Tyrosine Kinase ◽  
Cumulative Number ◽  
Phase 2 ◽  
Bruton's Tyrosine Kinase ◽  
Relapsing Remitting

: Significant progress has been made in understanding the immunopathogenesis of multiple sclerosis (MS) over recent years. Successful clinical trials with CD20-depleting monoclonal antibodies have corroborated the fundamental role of B cells in the pathogenesis of MS and reinforced the notion that cells of the B cell lineage are an attractive treatment target. Therapeutic inhibition of Bruton's tyrosine kinase (BTK), an enzyme involved in B cell and myeloid cell activation and function, is regarded as a next-generation approach that aims to attenuate both errant innate and adaptive immune functions. Moreover, brain-penetrant BTK inhibitors may impact compartmentalized inflammation and neurodegeneration within the central nervous system by targeting brain-resident B cells and microglia, respectively. Preclinical studies in animal models of MS corroborated an impact of BTK inhibition on meningeal inflammation and cortical demyelination. Notably, BTK inhibition attenuated the antigen-presenting capacity of B cells and the generation of encephalitogenic T cells. Evobrutinib, a selective oral BTK inhibitor, has been tested recently in a phase 2 study of patients with relapsing-remitting MS. The study met the primary endpoint of a significantly reduced cumulative number of Gadolinium-enhancing lesions under treatment with evobrutinib compared to placebo treatment. Thus, the results of ongoing phase 2 and 3 studies with evobrutinib, fenobrutinib, and tolebrutinib in relapsing-remitting and progressive MS are eagerly awaited. This review article introduces the physiological role of BTK, summarizes the pre-clinical and trial evidence, and addresses the potential beneficial effects of BTK inhibition in MS.

scholarly journals Central human B cell tolerance manifests with a distinctive cell phenotype and is enforced via CXCR4 signaling in hu-mice

2021 ◽  
Vol 118 (16) ◽  
pp. e2021570118
Author(s):  
Thiago Alves da Costa ◽  
Jacob N. Peterson ◽  
Julie Lang ◽  
Jeremy Shulman ◽  
Xiayuan Liang ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Immune System ◽  
B Cells ◽  
B Cell ◽  
Cell Tolerance ◽  
Human Immune System ◽  
B Cell Tolerance ◽  
Autoreactive B Cells ◽  
Cell Clones ◽  
Human Immune

Central B cell tolerance, the process restricting the development of many newly generated autoreactive B cells, has been intensely investigated in mouse cells while studies in humans have been hampered by the inability to phenotypically distinguish autoreactive and nonautoreactive immature B cell clones and the difficulty in accessing fresh human bone marrow samples. Using a human immune system mouse model in which all human Igκ+ B cells undergo central tolerance, we discovered that human autoreactive immature B cells exhibit a distinctive phenotype that includes lower activation of ERK and differential expression of CD69, CD81, CXCR4, and other glycoproteins. Human B cells exhibiting these characteristics were observed in fresh human bone marrow tissue biopsy specimens, although differences in marker expression were smaller than in the humanized mouse model. Furthermore, the expression of these markers was slightly altered in autoreactive B cells of humanized mice engrafted with some human immune systems genetically predisposed to autoimmunity. Finally, by treating mice and human immune system mice with a pharmacologic antagonist, we show that signaling by CXCR4 is necessary to prevent both human and mouse autoreactive B cell clones from egressing the bone marrow, indicating that CXCR4 functionally contributes to central B cell tolerance.

scholarly journals Active PI3K abrogates central tolerance in high-avidity autoreactive B cells

2019 ◽  
Vol 216 (5) ◽  
pp. 1135-1153 ◽  
Author(s):  
Sarah A. Greaves ◽  
Jacob N. Peterson ◽  
Pamela Strauch ◽  
Raul M. Torres ◽  
Roberta Pelanda
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Peripheral Tolerance ◽  
High Avidity ◽  
Cell Tolerance ◽  
B Cell Tolerance ◽  
Central Tolerance ◽  
Autoreactive B Cells ◽  
Self Antigen

Autoreactive B cells that bind self-antigen with high avidity in the bone marrow undergo mechanisms of central tolerance that prevent their entry into the peripheral B cell population. These mechanisms are breached in many autoimmune patients, increasing their risk of B cell–mediated autoimmune diseases. Resolving the molecular pathways that can break central B cell tolerance could therefore provide avenues to diminish autoimmunity. Here, we show that B cell–intrinsic expression of a constitutively active form of PI3K-P110α by high-avidity autoreactive B cells of mice completely abrogates central B cell tolerance and further promotes these cells to escape from the bone marrow, differentiate in peripheral tissue, and undergo activation in response to self-antigen. Upon stimulation with T cell help factors, these B cells secrete antibodies in vitro but remain unable to secrete autoantibodies in vivo. Overall, our data demonstrate that activation of the PI3K pathway leads high-avidity autoreactive B cells to breach central, but not late, stages of peripheral tolerance.

Mucosal Epithelial Cells Initiate Frontline Immunoglobulin Class Switching through an SLPI-Regulated Pathway.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3898-3898
Author(s):  
Andrea Cerutti ◽  
Bing He ◽  
April Chiu ◽  
Meimei Shan ◽  
Paul Santini ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
B Cells ◽  
Epithelial Cells ◽  
B Cell ◽  
Antibody Production ◽  
Cytidine Deaminase ◽  
Dna Recombination ◽  
Class Switching ◽  
Class Switch

Abstract Introduction. Class switching from IgM to IgG and IgA is central to immunity against microbes and usually occurs in draining lymph nodes and requires activation of B cells by CD4+ T cells expressing CD40 ligand. Growing evidence indicates that B cells can mount frontline IgG and IgA responses at mucosal sites of entry through an alternative CD40-independent pathway involving B cell-activating factor of the TNF family (BAFF, also known as BLyS) and a proliferation-inducing ligand (APRIL). These innate factors are usually produced by dendritic cells and stimulate B cells through at least three distinct receptors. Together with dendritic cells, epithelial cells have a key position at the host-environment interface. Therefore, we asked whether epithelial cells play a role in frontline antibody production. Methods. Tonsillar tissue sections from healthy donors were analyzed for expression of activation-induced cytidine deaminase (AID) by immunohistochemistry and in situ hybridization. A simplified in vitro model reproducing the geometry of mucosal surfaces was used to evaluate the role of epithelial cells in class switching. Briefly, primary epithelial cells and B cells were cultured in the upper and lower chambers, respectively, of a trans-well system. Monocyte-derived dendritic cells were positioned on a filter separating the two chambers. Various microbial product analogues were used to mimic infection. RNA interference was performed to knockdown BAFF in epithelial cells. AID expression, CSR, antibody production and signaling were evaluated in B cells as reported (Litinsky et al., Nat. Immunol.2002, 3:822–829; Qiao et al., Nat. Immunol.2006, 7:302–310). Results. We found that the upper respiratory mucosa of healthy subjects comprised intraepithelial pockets filled with B cells expressing AID, a DNA-editing enzyme associated with ongoing class switch DNA recombination (CSR). Epithelial cells released innate class switch-inducing factors, including BAFF, after sensing microbial products through TLRs, thereby inducing AID expression, CSR, and ultimately IgG and IgA production in neighboring B cells. Epithelial cell-induced antibodies comprised polyreactive IgG and IgA capable of recognizing multiple microbial determinants. Intraepithelial class switching was enhanced by thymic stromal lymphopoietin (TSLP), an epithelial IL-7-like cytokine that augments the innate B cell-licensing functions of dendritic cells, and restrained by secretory leukocyte protease inhibitor (SLPI), an epithelial alarm antiprotease that suppresses AID expression in activated B cells. Conclusions. The present findings indicate that epithelial cells function as non-immune sentinels capable to autonomously orchestrate compartmentalized IgG and IgA responses at the interface between host and environment. This implies that mucosal vaccines should activate both epithelial and immune cells to elicit optimal antibody production.

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

Blood ◽  
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.

scholarly journals Impaired early B cell tolerance in patients with rheumatoid arthritis

2005 ◽  
Vol 201 (10) ◽  
pp. 1659-1667 ◽  
Author(s):  
Jonathan Samuels ◽  
Yen-Shing Ng ◽  
Claire Coupillaud ◽  
Daniel Paget ◽  
Eric Meffre
Keyword(s):  
Rheumatoid Arthritis ◽  
B Cells ◽  
B Cell ◽  
Cell Tolerance ◽  
B Cell Tolerance ◽  
Autoantibody Production ◽  
Autoreactive B Cells ◽  
Healthy Donors ◽  
Polyreactive Antibodies

Autoantibody production is a characteristic of most autoimmune diseases including rheumatoid arthritis (RA). The role of these autoantibodies in the pathogenesis of RA remains elusive, but they appear in the serum many years before the onset of clinical disease suggesting an early break in B cell tolerance. The stage of B cell development at which B cell tolerance is broken in RA remains unknown. We previously established in healthy donors that most polyreactive developing B cells are silenced in the bone marrow, and additional autoreactive B cells are removed in the periphery. B cell tolerance in untreated active RA patients was analyzed by testing the specificity of recombinant antibodies cloned from single B cells. We find that autoreactive B cells fail to be removed in all six RA patients and represent 35–52% of the mature naive B cell compartment compared with 20% in healthy donors. In some patients, RA B cells express an increased proportion of polyreactive antibodies that can recognize immunoglobulins and cyclic citrullinated peptides, suggesting early defects in central B cell tolerance. Thus, RA patients exhibit defective B cell tolerance checkpoints that may favor the development of autoimmunity.

scholarly journals Continued dysregulation of the B cell lineage promotes multiple sclerosis activity despite disease modifying therapies

F1000Research ◽  
2021 ◽  
Vol 10 ◽  
pp. 1305
Author(s):  
Ana C. Londoño ◽  
Carlos A. Mora
Keyword(s):  
Multiple Sclerosis ◽  
B Cells ◽  
B Cell ◽  
Cell Lineage ◽  
Clear Understanding ◽  
Cellular Activity ◽  
Regulatory B Cells ◽  
Disease Modifying Therapies

A clear understanding of the origin and role of the different subtypes of the B cell lineage involved in the activity or remission of multiple sclerosis (MS) is important for the treatment and follow-up of patients living with this disease. B cells, however, are dynamic and can play an anti-inflammatory or pro-inflammatory role, depending on their milieu. Depletion of B cells has been effective in controlling the progression of MS, but it can have adverse side effects. A better understanding of the role of the B cell subtypes, through the use of surface biomarkers of cellular activity with special attention to the function of memory and regulatory B cells (Bregs), will be necessary in order to offer specific treatments without inducing undesirable effects.

The Role of DNA Repair in the Pathogenesis of Activation Induced Cytidine Deaminase Dependent B Cell Lymphoma

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 397-397
Author(s):  
Xiwen Gu ◽  
Carmen J. Booth ◽  
David G. Schatz ◽  
Matthew P. Strout
Keyword(s):  
Dna Repair ◽  
B Cells ◽  
B Cell ◽  
Median Survival ◽  
Cell Lymphoma ◽  
Cytidine Deaminase ◽  
B Cell Lymphoma ◽  
Enzyme Activation ◽  
Activation Induced Cytidine Deaminase

Abstract Abstract 397 Upon antigenic stimulation of B cells, germinal centers (GCs) are formed where somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin (Ig) genes serve to diversify the immune response. SHM and CSR are initiated by the enzyme activation induced cytidine deaminase (AID) through the conversion of C/G base pairs to U-G mismatches. These mismatches are processed by UNG-dependent base excision repair (BER) and MSH2-dependent mismatch repair (MMR) pathways to yield mutations (for SHM) and DNA strand lesions (for CSR). Despite this essential role in immune diversification, the intrinsic activity of AID as a DNA mutator poses a threat to genomic integrity. Indeed, aberrant targeting of AID activity is associated with translocations and point mutations of proto-oncogenes associated with B cell malignancies. A specific dependence on AID in the pathogenesis of lymphomas of GC B cell origin is exemplified in Iμ-Bcl6 knock-in mice. These mice develop a diffuse large B cell lymphoma (DLBL) that resembles the human disease but are protected from development of this lymphoma when crossed onto an Aid-deficient background. To investigate the role of Aid-associated DNA repair in the pathogenesis of this disease, we crossed Iμ-Bcl6 mice onto a background deficient in BER (Ung−/−) and MMR (Msh2−/−). Young healthy Iμ-Bcl6 and Iμ-Bcl6 Ung−/−Msh2−/− mice displayed a normal number and distribution of B cells and normal architecture of lymphoid organs. Five of 28 Iμ-Bcl6 mice (17.9%) became sick starting at ∼12 months of age. Historically, median survival in these mice has not been reached and ∼80% survive to 15 months. In contrast, 21 of 28 Iμ-Bcl6 Ung−/−Msh2−/−mice (75%) developed disease with an onset of ∼3 months and had a median survival of 6.2 months (p<0.0001). All 5 of the Iμ-Bcl6 mice and the majority of Iμ-Bcl6 Ung−/−Msh2−/−mice developed B cell lymphoma with splenic involvement and variable nodal involvement. Five of the Iμ-Bcl6 Ung−/−Msh2−/−mice developed other cancers (3 T cell lymphomas, 1 pre-B cell lymphoma and 1 colon adenocarcinoma). Tumors from both genotypes expressed a mature B cell phenotype (B220+ IgM+ Igκ+ CD138-) and morphology revealed loss of normal lymphoid architecture with infiltration by lymphoid blasts. Additional staining demonstrated expression of at least one GC marker (Fas, GL7 and/or PNA). Similar to Iμ-Bcl6 mice, while many of the Iμ-Bcl6 Ung−/−Msh2−/−tumors had clonal mutated Ig heavy chain gene variable regions, two of the tumors were identified as oligoclonal, suggesting a preceding lymphoproliferative stage. In the absence of Ung and Msh2, Aid-generated U-G mismatches are not recognized and are simply replicated, causing only C/G to T/A transition mutations and no strand lesions. Thus, as expected, all Ig mutations in Iμ-Bcl6 Ung−/−Msh2−/−mice were C/G to T/A transitions. Lymphomas from Iμ-Bcl6 mice have been found to harbor numerous chromosome translocations and aneuploidies. Although additional analyses are underway, spectral karyotyping of 3 Iμ-Bcl6 Ung−/−Msh2−/−tumors revealed 2 with normal cytogenetics and 1 with a 40–41,XX,t(2;17),+15,+19. Surprisingly, sequence analysis of several known Aid target genes (cMyc, Pim1, RhoH, Pax5, Cd79a, Fas, H2ax and OcaB) in tumors from 3 Iμ-Bcl6 Ung−/−Msh2−/− mice did not identify any clonal mutations. However, non-clonal C/T to T/A transition mutations in cMyc were present at a frequency of 1.2 × 10−4, suggestive of ongoing Aid activity. The presence of Aid activity but absence of off-target Aid-mediated clonal SHM suggests that either other genes are targeted by Aid or that Aid has a secondary role in lymphomagenesis such as epigenetic reprogramming, as has been shown in iPS cells. Nonetheless, the incidence of Aid-dependent lymphomagenesis in the absence of Aid-associated DNA repair is significantly increased and the latency is greatly shortened. Altogether, this data suggests that Aid-associated BER and MMR pathways afford a protective effect against the development of Aid-dependent GC B cell lymphomas such as DLBL. To investigate the role of the individual Aid-associated DNA repair pathways, we have also generated Iμ-Bcl6 Ung−/− and Iμ-Bcl6 Msh2−/− single knockout mice. These studies are ongoing but preliminary results suggest that while the effect of Ung and Msh2 deficiency on lymphomagenesis may be synergistic, Msh2 might play a more critical role in preventing Aid-mediated genomic instability. Disclosures: No relevant conflicts of interest to declare.

scholarly journals B Cells Modulate Systemic Responses to Pneumocystis murina Lung Infection and Protect On-Demand Hematopoiesis via T Cell-Independent Innate Mechanisms when Type I Interferon Signaling Is Absent

2014 ◽  
Vol 83 (2) ◽  
pp. 743-758 ◽  
Author(s):  
Teri R. Hoyt ◽  
Erin Dobrinen ◽  
Irina Kochetkova ◽  
Nicole Meissner
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Lung Infection ◽  
Type I ◽  
Type I Ifn ◽  
Content Type ◽  
On Demand ◽  
Type I Ifns

HIV infection results in a complex immunodeficiency due to loss of CD4+T cells, impaired type I interferon (IFN) responses, and B cell dysfunctions causing susceptibility to opportunistic infections such asPneumocystis murinapneumonia and unexplained comorbidities, including bone marrow dysfunctions. Type I IFNs and B cells critically contribute to immunity toPneumocystislung infection. We recently also identified B cells as supporters of on-demand hematopoiesis followingPneumocystisinfection that would otherwise be hampered due to systemic immune effects initiated in the context of a defective type I IFN system. While studying the role of type I IFNs in immunity toPneumocystisinfection, we discovered that mice lacking both lymphocytes and type I IFN receptor (IFrag−/−) developed progressive bone marrow failure following infection, while lymphocyte-competent type I IFN receptor-deficient mice (IFNAR−/−) showed transient bone marrow depression and extramedullary hematopoiesis. Lymphocyte reconstitution of lymphocyte-deficient IFrag−/−mice pointed to B cells as a key player in bone marrow protection. Here we define how B cells protect on-demand hematopoiesis followingPneumocystis lung infection in our model. We demonstrate that adoptive transfer of B cells into IFrag−/−mice protects early hematopoietic progenitor activity during systemic responses toPneumocystisinfection, thus promoting replenishment of depleted bone marrow cells. This activity is independent of CD4+T cell help and B cell receptor specificity and does not require B cell migration to bone marrow. Furthermore, we show that B cells protect on-demand hematopoiesis in part by induction of interleukin-10 (IL-10)- and IL-27-mediated mechanisms. Thus, our data demonstrate an important immune modulatory role of B cells duringPneumocystislung infection that complement the modulatory role of type I IFNs to prevent systemic complications.

AID constrains germinal center size by rendering B cells susceptible to apoptosis

Blood ◽  
2009 ◽  
Vol 114 (3) ◽  
pp. 547-554 ◽  
Author(s):  
Ahmad Zaheen ◽  
Bryant Boulianne ◽  
Jahan-Yar Parsa ◽  
Shaliny Ramachandran ◽  
Jennifer L. Gommerman ◽  
...  
Keyword(s):  
Bone Marrow ◽  
B Cells ◽  
B Cell ◽  
Germinal Center ◽  
Cytidine Deaminase ◽  
Enzyme Activation ◽  
Specific Enzyme ◽  
Tissue Microenvironment ◽  
Activation Induced Cytidine Deaminase ◽  
Immunoglobulin Locus

Abstract The germinal center (GC) is a transient lymphoid tissue microenvironment that fosters T cell–dependent humoral immunity. Within the GC, the B cell–specific enzyme, activation-induced cytidine deaminase (AID), mutates the immunoglobulin locus, thereby altering binding affinity for antigen. In the absence of AID, larger GC structures are observed in both humans and mice, but the reason for this phenomenon is unclear. Because significant apoptosis occurs within the GC niche to cull cells that have acquired nonproductive mutations, we have examined whether a defect in apoptosis could account for the larger GC structures in the absence of AID. In this report, we reveal significantly reduced death of B cells in AID−/− mice as well as in B cells derived from AID−/− bone marrow in mixed bone marrow chimeric mice. Furthermore, AID-expressing B cells show decreased proliferation and survival compared with AID−/− B cells, indicating an AID-mediated effect on cellular viability. The GC is an etiologic site for B-cell autoimmunity and lymphomagenesis, both of which have been linked to aberrant AID activity. We report a link between AID-induced DNA damage and B-cell apoptosis that has implications for the development of B-cell disorders.

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