Infective Endocarditis Complicated With a Large Left Coronary Cusp Aneurysm: A Condition With Undefined Natural History and Treatment.

The natural history and treatment of an aortic cusp aneurysm with or without rupture because of native aortic valve infective endocarditis (NAV-IE) have not been well defined. This may explain why current guidelines for the management of valvular heart disease do not include this complication as an indication for surgical aortic valve replacement or repair or transcatheter aortic valve replacement (TAVR). We describe herein the first case of a man aged 76 years with multiple co-morbidities with a NAV-IE associated large left coronary cusp aneurysm with subsequent rupture and consequent severe aortic regurgitation and heart failure for which he underwent an off-label successful TAVR. This patient's scenario suggests that a cusp aneurysm because of NAV-IE poses a high risk for subsequent rupture, severe aortic regurgitation, and heart failure. In conclusion, TAVR may be a reasonable alternative to high-risk surgical aortic valve replacement in patients with NAV-IE associated cusp aneurysms with or without but impending rupture.

Side-by-Side Comparison of Compensation Beads Used in Polychromatic Flow Cytometry.

Compensation or unmixing is essential in analyzing multiparameter flow cytometry data. Errors in data correction, either by compensation or unmixing, can completely change the outcome or mislead the researchers. Owing to limited cell numbers, researchers often use synthetic beads to generate the required single stains for the necessary calculation. In this study, the capacity of synthetic beads to influence data correction is evaluated. Corrected data for human peripheral blood cells were generated using cell-based compensation from the same cells or bead-based compensation to identify differences between the methods. These data suggest that correction with beads on full-spectrum and conventional cytometers does not always follow the basic flow compensation/unmixing expectations and alters the data. Overall, the best approach for bead-based correction for an experiment is to evaluate which beads and fluorochromes are most accurately compensated/unmixed.

A gain and dynamic range independent index to quantify spillover spread to aid panel design in flow cytometry.

In conventional flowcytometry one detector (primary) is dedicated for one fluorochrome. However, photons usually end up in other detectors too (fluorescence spillover). 'Compensation' is a process that corrects the spillover signal from all detectors except the primary detector. Post 'compensation', the photon counting error of spillover signals become evident as spreading of the data. The spreading induced by spillover impairs the ability to resolve stained cell population from the unstained one, potentially reducing or completely losing cell populations. For successful multi-color panel design, it is important to know the expected spillover to maximize the data resolution. The Spillover Spreading Matrix (SSM) can be used to estimate the spread, but the outcome is dependent on detector sensitivity. Simply, the same single stained sample produces different spillover spread values when detector(s) sensitivity is altered. Many researchers mistakenly use this artifact to "reduce" the spread by decreasing detector sensitivity. This can result in diminished capacity to resolve dimly expressing cell populations. Here, we introduce SQI (Spread Quantification Index), that can quantify the spillover spread independent of detector sensitivity and independent of dynamic range. This allows users to compare spillover spread between instruments having different types of detectors, which is not possible using SSM.

Aortic adventitial thickness as a marker of aortic atherosclerosis, vascular stiffness, and vessel remodeling in systemic lupus erythematosus.

INTRODUCTION: There is limited human imaging data on the association of adventitial thickness (AT) with arterial disease. Systemic lupus erythematosus (SLE) is a prototypical disease model for studying markers of premature arterial disease. OBJECTIVE: To determine if increased aortic AT is associated with aortic atherosclerosis [increased intima media thickness (IMT) or plaques], stiffness [increased pressure-strain elastic modulus (PSEM)], and vessel remodeling. METHODS: In total, 70 SLE patients and 26 age- and sex-matched controls underwent transesophageal echocardiography (TEE). Two-dimensional guided M-mode images were obtained to assess AT, IMT, and plaques, and PSEM at the proximal, mid, and distal thoracic aorta. Images were interpreted by 3 observers unaware of the subjects' clinical data and each other's measurements. Abnormal aortic AT, IMT, and PSEM were defined as > 2SD above the overall mean values in controls and corresponded to > 1 mm, > 1 mm, and > 10.6 Pascal units, respectively. Plaques were defined as focal-protruding IMT > 50% of the surrounding vessel wall. RESULTS: Abnormal aortic AT, atherosclerosis, and abnormal stiffness were more frequent in SLE patients than in controls (all p ≤ 0.02). In SLE patients, abnormal AT combined with atherosclerosis was associated with larger aortic end-diastolic diameters than in controls (p ≤ 0.05). In SLE patients, aortic AT was greater in patients with atherosclerosis and in those with abnormal stiffness than in patients without these abnormalities (all p ≤ 0.02). In patients with abnormal AT, the degree of aortic stiffness was similar to those with atherosclerosis (p = 0.22). CONCLUSION: In patients with SLE, increased aortic AT is associated with aortic atherosclerosis, abnormal stiffness, and eccentric vessel remodeling. Key Points • In patients with SLE, abnormal aortic adventitial thickness is associated with aortic atherosclerosis, abnormal stiffness, and eccentric vessel remodeling. • In patients with SLE, aortic adventitial thickening may contribute to the extent of aortic atherosclerosis, abnormal aortic stiffness, and vessel remodeling. • To our knowledge, this is the first human imaging study to characterize the aortic adventitial layer and delineate its association with aortic disease.

ARID3a expression in human hematopoietic stem cells is associated with distinct gene patterns in aged individuals.

BACKGROUND: Immunologic aging leads to immune dysfunction, significantly reducing the quality of life of the elderly. Aged-related defects in early hematopoiesis result in reduced lymphoid cell development, functionally defective mature immune cells, and poor protective responses to vaccines and pathogens. Despite considerable progress understanding the underlying causes of decreased immunity in the elderly, the mechanisms by which these occur are still poorly understood. The DNA-binding protein ARID3a is expressed in a subset of human hematopoietic progenitors. Inhibition of ARID3a in bulk human cord blood CD34+ hematopoietic progenitors led to developmental skewing toward myeloid lineage at the expense of lymphoid lineage cells in vitro. Effects of ARID3a expression in adult-derived hematopoietic stem cells (HSCs) have not been analyzed, nor has ARID3a expression been assessed in relationship to age. We hypothesized that decreases in ARID3a could explain some of the defects observed in aging. RESULTS: Our data reveal decreased frequencies of ARID3a-expressing peripheral blood HSCs from aged healthy individuals compared with young donor HSCs. Inhibition of ARID3a in young donor-derived HSCs limits B lineage potential, suggesting a role for ARID3a in B lymphopoiesis in bone marrow-derived HSCs. Increasing ARID3a levels of HSCs from aged donors in vitro alters B lineage development and maturation. Finally, single cell analyses of ARID3a-expressing HSCs from young versus aged donors identify a number of differentially expressed genes in aged ARID3A-expressing cells versus young ARID3A-expressing HSCs, as well as between ARID3A-expressing and non-expressing cells in both young and aged donor HSCs. CONCLUSIONS: These data suggest that ARID3a-expressing HSCs from aged individuals differ at both molecular and functional levels compared to ARID3a-expressing HSCs from young individuals.

TLR engagement induces ARID3a in human blood hematopoietic progenitors and modulates IFNα production.

The DNA binding protein AT-rich interacting domain 3a (ARID3a)2 is expressed in healthy human hematopoietic cord blood progenitors where its modulation influences myeloid versus B lineage development. ARID3a is also variably expressed in subsets of adult peripheral blood hematopoietic progenitors where the consequences of ARID3a expression are unknown. In B lymphocytes, Toll-like receptor (TLR)3 signaling induces ARID3a expression in association with Type I interferon inflammatory cytokines. We hypothesized that TLR ligand stimulation of peripheral blood hematopoietic progenitors would induce ARID3a expression resulting in interferon production, and potentially influencing lineage decisions. Our data revealed that the TLR9 agonist CpG induces ARID3a expression with interferon alpha synthesis in human hematopoietic progenitors. However, ARID3a expression was not associated with increased B lineage development. These results demonstrate the need for further experiments to better define how pathogen-associated responses influence hematopoiesis.

Transesophageal Versus Transthoracic Echocardiography for Assessment of Left Ventricular Diastolic Function.

Background: Transesophageal echocardiography (TEE) has not been compared to transthoracic echocardiography (TTE) for assessment of left ventricular diastolic function (LVDF). Left ventricular diastolic dysfunction is common in systemic lupus erythematosus (SLE), a disease model of premature myocardial disease. Methods: 66 patients with SLE (mean age 36±12 years, 91% women) and 26 age-and-sex matched healthy volunteers (mean age 34±11 years, 85% women) underwent TEE immediately followed by TTE. From basal four-chamber views, mitral inflow E and A velocities, E/A ratio, E deceleration time, isovolumic relaxation time, septal and lateral mitral E' and A' velocities, septal E'/A' ratio, mitral E to septal and lateral E' ratios, and pulmonary veins systolic to diastolic peak velocities ratio were measured. Measurements were averaged over 3 cardiac cycles and performed by 2 independent observers. Results: LVDF parameters were worse in patients than in controls by TEE and TTE (all p≤0.03). Most LVDF parameters were similar within each group by TEE and TTE (all p≥0.17). By both techniques, mitral E and A, mitral and septal E/A ratios, septal and lateral E', septal and lateral E/E' ratios, and average E/E' ratio were highly correlated (r=0.64-0.96, all p≤0.003); E deceleration time, isovolumic relaxation time, and septal A' velocities were moderately correlated (r=0.43-0.54, all p≤0.03); and pulmonary veins systolic to diastolic ratio showed the lowest correlation (r=0.27, p=0.04). Conclusion: By TEE and TTE, LVDF parameters were worse in SLE patients than in controls; and in both groups, LVDF parameters assessed by TEE and TTE were similar and significantly correlated.

New Frontiers: ARID3a in SLE.

Systemic lupus erythematosus (SLE) is a devastating and heterogeneous autoimmune disease that affects multiple organs, and for which the underlying causes are unknown. The majority of SLE patients produce autoantibodies, have increased levels of type-I inflammatory cytokines, and can develop glomerulonephritis. Recent studies indicate an unexpected but strong association between increased disease activity in SLE patients and the expression of the DNA-binding protein ARID3a (A + T rich interaction domain protein 3a) in a number of peripheral blood cell types. ARID3a expression was first associated with autoantibody production in B cells; however, more recent findings also indicate associations with expression of the inflammatory cytokine interferon alpha in SLE plasmacytoid dendritic cells and low-density neutrophils. In addition, ARID3a is expressed in hematopoietic stem cells and some adult kidney progenitor cells. SLE cells expressing enhanced ARID3a levels show differential gene expression patterns compared with homologous healthy control cells, identifying new pathways potentially regulated by ARID3a. The associations of ARID3a expression with increased disease severity in SLE, suggest that it, or its downstream targets, may provide new therapeutic targets for SLE.

ARID3a gene profiles are strongly associated with human interferon alpha production.

Type I interferons (IFN) causes inflammatory responses to pathogens, and can be elevated in autoimmune diseases such as systemic lupus erythematosus (SLE). We previously reported unexpected associations of increased numbers of B lymphocytes expressing the DNA-binding protein ARID3a with both IFN alpha (IFNα) expression and increased disease activity in SLE. Here, we determined that IFNα producing low density neutrophils (LDNs) and plasmacytoid dendritic cells (pDCs) from SLE patients exhibit strong associations between ARID3a protein expression and IFNα production. Moreover, SLE disease activity indices correlate most strongly with percentages of ARID3a+ LDNs, but were also associated, less significantly, with IFNα expression in LDNs and pDCs. Hierarchical clustering and transcriptome analyses of LDNs and pDCs revealed SLE patients with low ARID3a expression cluster with healthy controls and identified gene profiles associated with increased proportions of ARID3a- and IFNα-expressing cells of each type. These data identify ARID3a as a potential transcription regulator of IFNα-related inflammatory responses and other pathways important for SLE disease activity.

In old BALB/c mice, bone marrow pre-B cell and surrogate light chain reduction is associated with increased B cell reactivity to phosphorylcholine, but reduced T15 idiotype dominance.

In young adult BALB/c mice, antibodies to phosphorylcholine (PC) bearing the T15 (TEPC 15) idiotype confer protection against pneumococcal infections. In old age, even though PC reactive B cells are often increased, the proportion of T15+ antibodies declines. We hypothesize that limited surrogate light chain (SLC) and compromise of the pre-B cell receptor checkpoint in old mice contribute to both reduced new B cell generation and changes in the anti-PC antibodies seen in old age. In old mice: 1) early pre-B cell loss is most pronounced at the preBCR checkpoint; however, the reduced pool of early pre-B cells continues to proliferate consistent with preBCR signaling; 2) increased PC reactivity is seen in bone marrow immature B cells; 3) deficient SLC promotes increased B cell PC reactivity and diminished T15 idiotype expression; and 4) as pre-B cell losses and reduced SLC become progressively more severe, increased T15 negative PC reactive B cells occur. These results associate a reduction in pre-B cells, imposed at the preBCR checkpoint, with increased reactivity to PC, but more limited expression of the protective T15 idiotype among PC reactive antibodies in old age.

Expression and methylation data from SLE patient and healthy control blood samples subdivided with respect to ARID3a levels.

Previously published studies revealed that variation in expression of the DNA-binding protein ARID3a in B lymphocytes from patients with systemic lupus erythematosus (SLE) correlated with levels of disease activity ("Disease activity in systemic lupus erythematosus correlates with expression of the transcription factor AT-rich-interactive domain 3A" (J.M. Ward, K. Rose, C. Montgomery, I. Adrianto, J.A. James, J.T. Merrill et al., 2014) [1]). The data presented here compare DNA methylation patterns from SLE peripheral blood mononuclear cells obtained from samples with high numbers of ARID3a expressing B cells (ARID3a(H)) versus SLE samples with normal numbers of ARID3a(+) B cells (ARID3a(N)). The methylation data is available at the gene expression omnibus (GEO) repository, "Gene Expression Omnibus: NCBI gene expression and hybridization array data repository" (R. Edgar, M. Domrachev, A.E. Lash, 2002) [2]. Isolated B cells from SLE ARID3a(H) and ARID3a(N) B samples were also evaluated via qRT-PCR for Type I interferon (IFN) signature and pathway gene expression levels by qRT-PCR. Similarly, healthy control B cells and B cells stimulated to express ARID3a with the TLR agonist, CpG, were also compared via qRT-PCR. Primers designed to detect 6 IFNa subtype mRNAs were tested in 4 IFNa, Epstein-Barr Virus-transformed B cell lines ("Reduced interferon-alpha production by Epstein-Barr virus transformed B-lymphoblastoid cell lines and lectin-stimulated lymphocytes in congenital dyserythropoietic anemia type I" (S.H. Wickramasinghe, R. Hasan, J. Smythe, 1997) [3]). The data in this article support the publication, "Human effector B lymphocytes express ARID3a and secrete interferon alpha" (J.M. Ward, M.L. Ratliff, M.G. Dozmorov, G. Wiley, J.M. Guthridge, P.M. Gaffney, J.A. James, C.F. Webb, 2016) [4].

Human effector B lymphocytes express ARID3a and secrete interferon alpha.

Previously, we determined that enhanced disease activity in patients with systemic lupus erythematosus (SLE) was associated with dramatic increases in numbers of B lymphocytes expressing the transcription factor ARID3a. Our data now indicate ARID3a is important for interferon alpha (IFNa) expression and show a strong association between ARID3a expression and transcription of genes associated with lupus IFN signatures. Furthermore, both ARID3a and IFNa production were elicited in healthy control B cells upon stimulation with the TLR 9 agonist, CpG. Importantly, secretion of IFNa from ARID3a+ healthy B lymphocytes stimulated increased IFNa production in plasmacytoid dendritic cells. These data identify ARID3a+ B cells as a novel type of effector B cell, and link ARID3a expression in B lymphocytes to IFN-associated inflammatory responses in SLE.

The Transcription Factor ARID3a Is Important for In Vitro Differentiation of Human Hematopoietic Progenitors.

We recently reported that the transcription factor ARID3a is expressed in a subset of human hematopoietic progenitor stem cells in both healthy individuals and in patients with systemic lupus erythematosus. Numbers of ARID3a(+) lupus hematopoietic stem progenitor cells were associated with increased production of autoreactive Abs when those cells were introduced into humanized mouse models. Although ARID3a/Bright knockout mice died in utero, they exhibited decreased numbers of hematopoietic stem cells and erythrocytes, indicating that ARID3a is functionally important for hematopoiesis in mice. To explore the requirement for ARID3a for normal human hematopoiesis, hematopoietic stem cell progenitors from human cord blood were subjected to both inhibition and overexpression of ARID3a in vitro. Inhibition of ARID3a resulted in decreased B lineage cell production accompanied by increases in cells with myeloid lineage markers. Overexpression of ARID3a inhibited both myeloid and erythroid differentiation. Additionally, inhibition of ARID3a in hematopoietic stem cells resulted in altered expression of transcription factors associated with hematopoietic lineage decisions. These results suggest that appropriate regulation of ARID3a is critical for normal development of both myeloid and B lineage pathways.

A developmentally plastic adult mouse kidney cell line spontaneously generates multiple adult kidney structures.

Despite exciting new possibilities for regenerative therapy posed by the ability to induce pluripotent stem cells, recapitulation of three-dimensional kidneys for repair or replacement has not been possible. ARID3a-deficient mouse tissues generated multipotent, developmentally plastic cells. Therefore, we assessed the adult mouse ARID3a-/- kidney cell line, KKPS5, which expresses renal progenitor surface markers as an alternative cell source for modeling kidney development. Remarkably, these cells spontaneously developed into multicellular nephron-like structures in vitro, and engrafted into immunocompromised medaka mesonephros, where they formed mouse nephron structures. These data implicate KKPS5 cells as a new model system for studying kidney development.

In aged mice, low surrogate light chain promotes pro-B-cell apoptotic resistance, compromises the PreBCR checkpoint, and favors generation of autoreactive, phosphorylcholine-specific B cells.

In aged mice, new B-cell development is diminished and the antibody repertoire becomes more autoreactive. Our studies suggest that (i) apoptosis contributes to reduced B lymphopoiesis in old age and preferentially eliminates those B-cell precursors with higher levels of the surrogate light chain (SLC) proteins (λ5/VpreB) and (ii) λ5(low) B-cell precursors generate new B cells which show increased reactivity to the self-antigen/bacterial antigen phosphorylcholine (PC). Pro-B cells in old bone marrow as well as pro-B cells from young adult λ5-deficient mice are resistant to cytokine-induced apoptosis (TNFα; TGFß), indicating that low λ5 expression in pro-B cells is sufficient to cause increased survival. Transfer of TNFα-producing 'age-associated B cells' (ABC; CD21/35(-) CD23(-)) or follicular (FO) B cells from aged mice into RAG-2 KO recipients led to preferential loss of λ5(high) pro-B cells, but retention of λ5(low), apoptosis-resistant pro-B cells. In old mice, there is increased reactivity to PC in both immature bone marrow B cells and mature splenic FO B cells. In young mice, absence of λ5 expression led to a similar increase in PC reactivity among bone marrow and splenic B cells. We propose that in old age, increased apoptosis, mediated in part by TNFα-producing B cells, results in preferential loss of SLC(high) pro-B cells within the bone marrow. Further B-cell development then occurs via an 'SLC(low)' pathway that not only impairs B-cell generation, but promotes autoreactivity within the naïve antibody repertoires in the bone marrow and periphery.

Differential expression of the transcription factor ARID3a in lupus patient hematopoietic progenitor cells.

Although hematopoietic stem/progenitor cells (HSPCs) are used for transplantation, characterization of the multiple subsets within this population in humans has lagged behind similar studies in mice. We found that expression of the DNA-binding protein, ARID3a, in mouse stem cells was important for normal development of hematopoietic lineages; however, progenitors expressing ARID3a in humans have not been defined. We previously showed increased numbers of ARID3a(+) B cells in nearly half of systemic lupus erythematosus (SLE) patients, and total numbers of ARID3a(+) B cells were associated with increased disease severity. Because expression of ARID3a in those SLE patients occurred throughout all B cell subsets, we hypothesized that ARID3a expression in patient HSPCs might also be increased relative to expression in healthy controls. Our data now show that ARID3a expression is not limited to any defined subset of HSPCs in either healthy controls or SLE patients. Numbers of ARID3a(+) HSPCs in SLE patients were increased over numbers of ARID3a(+) cells in healthy controls. Although all SLE-derived HSPCs exhibited poor colony formation in vitro compared with controls, SLE HSPCs with high numbers of ARID3a(+) cells yielded increased numbers of cells expressing the early progenitor marker, CD34. SLE HSPCs with high numbers of ARID3a(+) cells also more readily generated autoantibody-producing cells than HSPCs with lower levels of ARID3a in a humanized mouse model. These data reveal new functions for ARID3a in early hematopoiesis and suggest that knowledge regarding ARID3a levels in HSPCs could be informative for applications requiring transplantation of those cells.

The Bright Side of Hematopoiesis: Regulatory Roles of ARID3a/Bright in Human and Mouse Hematopoiesis.

ARID3a/Bright is a DNA-binding protein that was originally discovered for its ability to increase immunoglobulin transcription in antigen-activated B cells. It interacts with DNA as a dimer through its ARID, or A/T-rich interacting domain. In association with other proteins, ARID3a increased transcription of the immunoglobulin heavy chain and led to improved chromatin accessibility of the heavy chain enhancer. Constitutive expression of ARID3a in B lineage cells resulted in autoantibody production, suggesting its regulation is important. Abnormal ARID3a expression has also been associated with increased proliferative capacity and malignancy. Roles for ARID3a in addition to interactions with the immunoglobulin locus were suggested by transgenic and knockout mouse models. Over-expression of ARID3a resulted in skewing of mature B cell subsets and altered gene expression patterns of follicular B cells, whereas loss of function resulted in loss of B1 lineage B cells and defects in hematopoiesis. More recent studies showed that loss of ARID3a in adult somatic cells promoted developmental plasticity, alterations in gene expression patterns, and lineage fate decisions. Together, these data suggest new regulatory roles for ARID3a. The genes influenced by ARID3a are likely to play pivotal roles in lineage decisions, highlighting the importance of this understudied transcription factor.

Aortic Atherosclerosis in Systemic Lupus Erythematosus.

Aortic atherosclerosis (AoA) defined as intima-media thickening or plaques and aortic stiffness (AoS) also considered an atherosclerotic process and defined as decreased vessel distensibility (higher pulse pressure to achieve similar degree of vessel distension) are common in patients with SLE. Immune-mediated inflammation, thrombogenesis, traditional atherogenic factors, and therapy-related metabolic abnormalities are the main pathogenic factors of AoA and AoS. Pathology of AoA and AoS suggests an initial subclinical endothelialitis or vasculitis, which is exacerbated by thrombogenesis and atherogenic factors and ultimately resulting in AoA and AoS. Computed tomography (CT) for detection of arterial wall calcifications and arterial tonometry for detection of increased arterial pulse wave velocity are the most common diagnostic methods for detecting AoA and AoS, respectively. MRI may become a more applicable and accurate technique than CT. Although transesophageal echocardiography accurately detects earlier and advanced stages of AoA and AoS, it is semi-invasive and cannot be used as a screening method. Although imaging techniques demonstrate highly variable prevalence rates, on average about one third of adult SLE patients may have AoA or AoS. Age at SLE diagnosis; SLE duration; activity and damage; corticosteroid therapy; metabolic syndrome; chronic kidney disease; and mitral annular calcification are common independent predictors of AoA and AoS. Also, AoA and AoS are highly associated with carotid and coronary atherosclerosis. Earlier stages of AoA and AoS are usually subclinical. However, earlier stages of disease may be causally related or contribute to peripheral or cerebral embolism, pre-hypertension and hypertension, and increased left ventricular afterload resulting in left ventricular hypertrophy and diastolic dysfunction. Later stages of disease predisposes to visceral ischemia, aortic aneurysms and aortic dissection. Even earlier stages of AoA and AoS have been associated with increased cardiovascular and cerebrovascular morbidity and mortality of SLE patients. Aggressive non-steroidal immunosuppressive therapy and non-pharmacologic and pharmacologic interventions for control of atherogenic risk factors may prevent the development or progression of AoA and AoS and may decrease cardiovascular and cerebrovascular morbidity and mortality in SLE.

In senescence, age-associated B cells secrete TNFα and inhibit survival of B-cell precursors.

Aged mice exhibit ~ 5-10-fold increases in an ordinarily minor CD21/35(-) CD23(-) mature B-cell subset termed age-associated B cells (ABCs). ABCs from old, but not young, mice induce apoptosis in pro-B cells directly through secretion of TNFα. In addition, aged ABCs, via TNFα, stimulate bone marrow cells to suppress pro-B-cell growth. ABC effects can be prevented by the anti-inflammatory cytokine IL-10. Notably, CD21/35(+) CD23(+) follicular (FO) splenic and FO-like recirculating bone marrow B cells in both young and aged mice contain a subpopulation that produces IL-10. Unlike young adult FO B cells, old FO B cells also produce TNFα; however, secretion of IL-10 within this B-cell population ameliorates the TNFα-mediated effects on B-cell precursors. Loss of B-cell precursors in the bone marrow of old mice in vivo was significantly associated with increased ABC relative to recirculating FO-like B cells. Adoptive transfer of aged ABC into RAG-2 KO recipients resulted in significant losses of pro-B cells within the bone marrow. These results suggest that alterations in B-cell composition during old age, in particular, the increase in ABC within the B-cell compartments, contribute to a pro-inflammatory environment within the bone marrow. This provides a mechanism of inappropriate B-cell 'feedback' that promotes down-regulation of B lymphopoiesis in old age.