Biomedical subjects

Bonnie B Blomberg

Publications and source records attributed to Bonnie B Blomberg.

16 recordsLinked to original sources

PubMed2006

Aging murine B cells have decreased class switch induced by anti-CD40 or BAFF.

We previously demonstrated that in vitro stimulated splenic B cells from senescent mice are deficient in production of multiple class switch isotypes, class switch recombination (CSR), induction of the E2A-encoded transcription factor E47, and activation-induced cytidine deaminase (AID) which is necessary for CSR and somatic hypermutation. Both anti-CD40 as well as BAFF have been shown to be able to induce CSR. We have investigated the ability of BAFF/IL-4, as compared to anti-CD40/IL-4, to induce CSR to gamma(1) in splenic B cells from young and old mice. We found that anti-CD40/IL-4 is a better CSR stimulus than BAFF/IL-4 in young B cells, as measured by RT-PCR of post-switch transcripts and flow cytometry. CSR is reduced in old B cells and this is independent of the stimulus. AID and gamma(1)PSTs are significantly reduced in old B cells stimulated with anti-CD40/IL-4, but only slightly reduced with BAFF/IL-4. BAFF receptor mRNA expression (BAFF-R, TACI, and BCMA) is not affected by aging. The age-related decrease in CSR induced by anti-CD40/IL-4 is primarily associated with a decrease in E47, whereas the less affected response to BAFF/IL-4 is associated with decreases in both E47 and NF-kappaB. Therefore, NF-kappaB is not involved in the decreased response of old B cells to anti-CD40/IL-4. These differences in B cell responses to CD40/IL-4 and BAFF/IL-4 may help to explain the maintenance of TI vs TD responses in senescent mice.

Aging↗

PubMed2005

RNA stability of the E2A-encoded transcription factor E47 is lower in splenic activated B cells from aged mice.

We have demonstrated previously that DNA binding and protein expression of the E2A-encoded transcription factor E47 are lower in nuclear extracts of activated splenic B cells from old mice. In the present study, we address how E47 protein expression is regulated in aging. Results herein show that E2A mRNA levels were decreased in stimulated splenic B cells from old as compared with young mice. RNA stability assays showed that the rate of E2A mRNA decay was accelerated in stimulated splenic B cells from old mice, but E47 protein degradation rates were comparable in young vs aged B cells, indicating that the regulation of E47 expression in activated splenic B cells occurs primarily by mRNA stability. The rates of decay of other mRNAs showed that the increased mRNA degradation in aged splenic activated B cells is not a general phenomenon but restricted to a subset of mRNAs. We next investigated the signal transduction pathways controlling E2A mRNA expression and stability and found that p38 MAPK regulates E2A mRNA expression through increased mRNA stability and is down-regulated in aged activated B cells. Results show that inhibition of p38 MAPK significantly reduces E2A mRNA stability in both young and old B cells, further stressing the role of p38 MAPK in E2A RNA stabilization. These studies demonstrate that the transcription factor E2A, critical for many aspects of B cell function, is regulated by a novel mechanism in aging.

Aging↗

PubMed2005

Humoral immune response and B-cell functions including immunoglobulin class switch are downregulated in aged mice and humans.

Vaccinations are powerful tools for combating infections. Because of the age-related impairment in immune functions, the currently available vaccines are protecting only a small proportion of the elderly population. We, here, provide an overview of age-related changes in innate and adaptive immunity with particular emphasis to changes in antibody production with aging. We also summarize our results showing that the E2A-encoded transcription factor E47, which regulates many B cell functions including class switch recombination (CSR) and somatic hypermutation (SHM), is downregulated in splenic B cells from old mice. This leads to a reduction in the activation-induced cytidine deaminase (AID), which directly induces CSR and SHM, and, in turn, to reduced amounts of switched antibodies produced by splenic activated B cells. Our preliminary results in humans indicate similar reductions: we show herein that the expression of E2A and AID progressively decline with age. Our results provide a possible molecular basis for a decrease in the humoral immune response in aging mice and humans.

Aging↗

PubMed2005

Deficient B lymphopoiesis in murine senescence: potential roles for dysregulation of E2A, Pax-5, and STAT5.

B lymphopoiesis in senescent mice is typically diminished and characterized by low pre-B cell numbers. The transcription factors E2A, Pax-5, and STAT5 have been implicated in the differentiation, proliferation, and survival of B cell precursors. In this review, we discuss the impairment of B lymphopoiesis during old age in the context of mechanisms at the molecular level responsible for the handling and turnover of these key transcriptional proteins. Alterations in the expression of E2A, Pax-5, and STAT5 may affect multiple stages of B cell development, contribute to reduced B lymphopoiesis, and preface changes in the "read-out" of the BCR repertoire during murine senescence.

Aging↗

PubMed2005

B cells, E2A, and aging.

Both mouse and human exhibit deficiencies in humoral immunity during 'old age'. While alterations in phenotype and function have been well documented, the molecular mechanisms that result in immune senescence remain undefined. B lymphopoiesis is suppressed in senescent mice, which may result from deficits at the pre-B-cell stage or earlier (e.g. pro-B cells). This deficit contrasts with the maintenance of the normal number of total peripheral B lymphocytes in senescent mice. However, mature peripheral B cells in aged mice can exhibit reduced efficiencies of both immunoglobulin isotype switching and somatic hypermutation. The basic helix-loop-helix transcription factor E2A is crucial at several stages of B-lymphocyte differentiation, including the development of pro-B and pre-B cells within the bone marrow and in isotype switch and somatic hypermutation among peripheral B cells. Therefore, we have focused on the regulation of E2A expression and function during both B lymphopoiesis and isotype class switching in senescent mice. These studies show that E2A expression is normally under complex control at both post-transcriptional and post-translational levels. Alterations in E2A expression at both the B-cell precursor and mature B-cell developmental stages are hypothesized to contribute to defects in humoral immunity during senescence.

Aging↗

PubMed2004

Decreased E47 in senescent B cell precursors is stage specific and regulated posttranslationally by protein turnover.

The E2A-encoded transcription factor E47 is crucial to B lymphopoiesis. Senescent BALB/c mice ( approximately 2 years old) had reduced pre-B cells ex vivo. Pro-B/early pre-B cells from these aged mice, both ex vivo and in vitro, were deficient in E47 protein. In vitro, IL-7 expanded pro-B/early pre-B cells from young BALB/c mice expressed E47 protein that was relatively stable over a 5-h period. Cultured senescent pro-B/early pre-B cells exhibited reduced E47 protein stability with approximately 50-90% loss of E47 over the same time period. Degradation of E47 was effectively blocked by the proteasome inhibitor lactacystin as well as calpain I and II inhibitors; E2A proteins were also shown to undergo ubiquitination. Although senescent B cell precursors expressed less E47 protein, E47 mRNA levels and turnover were normal. Therefore, E47 protein levels are reduced relatively early in B lineage differentiation in senescence and the decline in E47 protein occurs via increased protein degradation by proteasome and, possibly, calpain pathways. In contrast, normal E47 protein levels were observed within the highly reduced pre-B cell pool in aged mice. This suggests that pre-B cells in senescence undergo selection based on E47 expression. Increased degradation rates and lower steady-state levels were also observed for the transcription factors Pax-5/BSAP, Bob-1, and Ikaros, but this was not a general property of all proteins in aged B cell precursors. Therefore, altered turnover of multiple, select proteins crucial to B cell development may contribute to diminished B lymphopoiesis in old age.

Animals↗

PubMed2004

Reduced Ig class switch in aged mice correlates with decreased E47 and activation-induced cytidine deaminase.

The capacity to class switch the IgH chain is critical to the effectiveness of humoral immune responses. We show that in vitro-stimulated splenic B cells from senescent mice are deficient in production of multiple class switch isotypes (IgG1, G2a, G3, and E), class switch recombination (CSR), and induction of the E2A-encoded transcription factor E47. E47 has previously been shown to be required for CSR, at least in part via expression of the activation-induced cytidine deaminase. Our studies show that impaired induction of E47, and subsequently activation-induced cytidine deaminase, contribute to poor CSR and production of secondary isotypes in senescence.

Aging↗

PubMed2004

Age-related differences in the E2A-encoded transcription factor E47 in bone marrow-derived B cell precursors and in splenic B cells.

We have investigated the effects of aging on the E2A-encoded transcription factor E47, a key regulator of B cell functions, in B cell precursors and in splenic B cells. Here, we show that old mice can be classified as severely depleted, moderately depleted or not depleted mice, according to the percentage of pre-B cells in their bone marrow. IL-7-expanded populations of pro-B/early pre-B cells from bone marrow of both severely depleted and moderately depleted old mice exhibit a reduced E47 DNA-binding and expression compared to young mice, and this defect in severely depleted old mice is more dramatic than that in moderately depleted old mice. However, mRNA levels were comparable, suggesting that E47 in the bone marrow is not transcriptionally regulated. In the spleen, activated B cells from both severely depleted and moderately depleted old mice show a lower E47 DNA-binding and expression than young mice. However, in contrast to precursor B cells, E47 DNA-binding and expression are similarly and only moderately reduced in both severely depleted and in moderately depleted mice. The mRNA levels were found to be decreased in stimulated splenic B cells from old as compared to young mice, suggesting that E47 mRNA in the spleen may be both transcriptionally and/or post-transcriptionally regulated.

Aging↗

PubMed2004

Effects of aging on DNA-binding activity of the E47 transcription factor in splenic B cells.

In the present paper, we have investigated the DNA-binding activity of the E2A-encoded transcription factor E47 in LPS-activated splenic B cells from young and old BALB/c mice. E47 is a key regulator of B cell differentiation and function: it binds to the E-box site, found in the regulatory regions of several B cell-specific genes (immunoglobulin (Ig), mb-1, and lambda5), promotes cell survival of early pre-B cells, helps to initiate Ig rearrangements, promotes class switch and is perhaps involved in somatic mutation in mature splenic and lymph node B cells. Results show that LPS-stimulated splenic B cells from old mice display decreased E47 DNA-binding activity as compared to young mice and that in splenic activated B cells only E47 homodimers bind DNA.

Aging↗

PubMed2004

Cognitive-behavioral stress management increases benefit finding and immune function among women with early-stage breast cancer.

OBJECTIVE: This study examined the effect of a cognitive-behavioral stress management (CBSM) intervention on emotional well-being and immune function among women in the months following surgery for early-stage breast cancer. METHOD: Twenty-nine women were randomly assigned to receive either a 10-week CBSM intervention (n=18) or a comparison experience (n=11). The primary psychological outcome measure was benefit finding. The primary immune function outcome measure was in vitro lymphocyte proliferative response to anti CD3. RESULTS: Women in the CBSM intervention reported greater perceptions of benefit from having breast cancer compared to the women in the comparison group. At 3-month follow-up, women in the CBSM group also had improved lymphocyte proliferation. Finally, increases in benefit finding after the 10-week intervention predicted increases in lymphocyte proliferation at the 3-month follow-up. CONCLUSION: A CBSM intervention for women with early-stage breast cancer facilitated positive emotional responses to their breast cancer experience in parallel with later improvement in cellular immune function.

Adult↗

PubMed2004

Effect of age on the immunoglobulin class switch.

Aging represents a complex remodelling in which both specific and innate immunity deteriorate. Age-related changes in humoral immunity involve reduced vaccine responses and increased production of auto-antibodies. Although T-cell alterations play a significant role in age-related humoral immune changes, alterations in B cells also occur. In this review, we provide an overview of age-related changes in B-cell functions and markers, including transcription factors, and also discuss controversies in the field of B-cell aging. We summarize our recent results, showing that splenic B cells from senescent mice are deficient in production of secondary isotypes (IgG1, IgG2a, IgG3, IgE), class switch recombination (CSR), and expression of the transcription factor E47. We also demonstrate that there is more Id2 (a negative regulator of E47) in old activated B cells. E47 is required for CSR, at least in part, via expression of activation-induced cytidine deaminase (AID). Our studies show that impaired induction of E47, and, subsequently, AID, contribute to poor CSR and production of secondary isotypes in senescence. We also present new data indicating the absence of DNA switch region excision circles for CSR in old activated B cells, confirming the location of the defect at the DNA endonucleolytic step. And, finally, we show that there is no change in NF-kappaB or Blimp-1 in old vs young stimulated B cells.

Age Factors↗

PubMed2003

The age-related decrease in E47 DNA-binding does not depend on increased Id inhibitory proteins in bone marrow-derived B cell precursors.

Our previous results showed that decreased numbers of pre-B cells in aged mice were associated with decreases in surrogate light chain, lambda5, and transcription factors E47/E12. In the present paper, we have analyzed IL-7-expanded populations of pro-B/early pre-B cells to evaluate whether the age-related reduction in E47 DNA-binding could be attributed to reduced E47 expression and/or increased Id expression. According to the percentage of pre-B cells present in their bone marrow, old mice were classified as severely depleted (>80% loss in pre-B cells, 50% loss in pro-B cells), or moderately depleted (20-80% loss in pre-B cells). Results herein show that IL-7-stimulated pro-B/pre-B cells from both severely depleted and moderately depleted old mice exhibit a reduced E47 DNA-binding capacity compared to young mice, and this defect in severely depleted old mice is more dramatic than that in moderately depleted old mice. Id proteins, which are inhibitors of E47, are not increased in nuclear extracts of IL-7-expanded pro-B/early pre-B cells from severely depleted or moderately depleted old mice. We therefore conclude that the reduced expression of E47 protein alone in severely depleted and to a lesser extent in moderately depleted old mice explains the reduced amount of E47-DNA binding.

Age Factors↗

PubMed2003

Decreased E12 and/or E47 transcription factor activity in the bone marrow as well as in the spleen of aged mice.

The E2A-encoded transcription factors E12 and E47 are key regulators of B cell functions. They bind to the E-box site, found in regulatory regions of B cell-specific genes; promote cell survival of early pre-B cells; help to initiate Ig rearrangements; and are also involved in class switch in mature B cells in the periphery. We have investigated the expression and function of E47 and E12 in IL-7-expanded pro-B/pre-B cell precursors and in unstimulated or LPS-activated splenic B cells from young and old BALB/c mice. Results show that B cell precursors from the bone marrow of old mice exhibit a reduced expression of E2A proteins and a reduced ability to bind DNA, as compared with young mice. In the spleen, E2A protein expression and DNA binding are present in unstimulated B cells from young mice and, to a significantly lesser extent, from old mice. These are both strongly induced by activation in splenic B cells from young mice but only moderately induced in old mice, indicating that aging affects the expression and activity of E2A-encoded genes and also that DNA binding correlates with the amount of protein expression. The levels of E2A DNA binding in the spleen correlate with those in the bone marrow for individual mice. In splenic mature B cells, only E47/E47 complexes bind DNA; whereas in bone marrow B cell precursors, E47/E12 complexes participate in DNA binding. Only nuclear extracts of splenic mature B cells, but both nuclear and cytoplasmic extracts of bone marrow B cell precursors, exhibit DNA binding.

Aging↗

PubMed2003

Aged mice exhibit distinct B cell precursor phenotypes differing in activation, proliferation and apoptosis.

Senescence in murine models is associated with a reduction, albeit heterogeneous, in bone marrow pre-B cells. We have categorized aged BALB/c mice into two phenotypes based on their patterns of pre-B/pro-B cell loss. Each phenotype is characterized by distinct responses to the growth cytokine IL-7 and capacity for survival in vitro. A 'moderate' loss of late-stage pre-B cells (25-80%) coincided with decline in proliferation to rmIL-7. This was also associated with a decrease in the frequency of pro-B cells which increased phosphotyrosine content upon IL-7 stimulation, an indicator of early activation events. A 'severe' loss of pre-B cells (>80%) resulted in a reduced pro-B cell pool which retained normal activation and proliferative responses to IL-7. B cell precursors from aged mice with severe alterations in B lymphopoiesis displayed increased susceptibility to apoptosis in comparison to both aged mice with moderate B cell precursor loss and young mice. Conceivably, during senescence, aged mice may initially accumulate B cell precursors which are poorly responsive to IL-7. Progressively, these refractory B cell precursors may be eliminated via apoptosis; however, the remaining limited pool of B cell precursors retains the capacity to respond to IL-7 stimulation.

Aging↗

PubMed2003

Effects of aging on proliferation and E47 transcription factor activity induced by different stimuli in murine splenic B cells.

In the present paper, we have investigated the effects of aging on the expression and function of the E2A-encoded transcription factor E47 in splenic B lymphocytes, unactivated or activated with different stimuli (LPS, anti-CD40, anti-IgM, alone or in combination with IL-4). Results indicate that unstimulated splenic B cells show very low E47 protein levels as well as E47 DNA-binding activity and that, upon B cell activation, E47 expression and DNA-binding activity are strongly induced in young and, to a significantly lesser extent, in old mice. The level of E47 protein expression in stimulated splenic B cells was found significantly higher in young than in old mice, suggesting that DNA-binding activity correlates with protein expression. These results altogether suggest that the reduced expression of the transcriptional regulator E47 could help explain the reduced B cell functions in aging mice.

Aging↗

PubMed2002

Functional and phenotypic properties of peripheral T cells anergized by autologous CD3(+) depleted bone marrow cells.

We have previously demonstrated that bone marrow cells (BMC) inhibit the generation of autologous Epstein-Barr virus (EBV) -specific cytotoxic T lymphocytes (CTL). It was also observed that CD3(+) cells obtained after 7 days of culture in the presence of autologous BMC could be used as inhibitors of EBV-CTL generation. In the present study, we examined these BMC induced regulator CD3(+) T cells with respect to phenotype, function, and T-cell activation pathways. We also questioned if the CD3(+) regulatory cell function is mediated by their direct effect on peripheral T cells or on the ability of antigen presenting cells (APC) to stimulate peripheral T cells. To answer this, CD3(+) cells from peripheral blood lymphocytes (PBL) were cultured with either CD3-depleted BMC or with CD3-depleted PBL. The CD3(+) cells were then isolated with immunomagnetic beads, designated as T(BM) and T(PBL), and were compared in functional studies. There was an increase in the expression of CD25 on T(BM) cells. The T(BM) cells also expressed less CD122 and a decreased number of CD3 molecules per cell. Both T(BM) and T(PBL) cell populations responded to mitogen (PHA) to the same magnitude. However, when stimulated through the CD3 complex with anti-CD3 monoclonal antibody (mAb), the T(BM) cells had a significantly decreased response than did T(PBL). The addition of IL-2 to these latter cultures augmented, but could not fully restore, the response. Additionally, stimulation of T(BM) cells with allogeneic cells failed to produce cytotoxic T cells. These "anergized" T(BM) and "nonanergized" (control) T(PBL) cells were added as third-party cells to a CTL generating culture of autologous PBL stimulated with allogeneic cells. The T(BM) cells exhibited suppressor function and inhibited the generation of CTL, in contrast with T(PBL). The effect of T(BM) cells on direct and indirect antigen presentation pathways demonstrated that T(BM) primarily effected indirect, but not direct, alloantigen presentation. To further explore the cytoplasmic T-cell activation events that occurred after the coculture of the PBL T cells with BMC, the levels of zeta-associated protein 70 (ZAP70) and extracellular receptor-activated kinase (ERK) were determined. There was a decrease in ZAP70 levels in the T(BM), which correlated with its reduced expression of cell surface CD3 and the attenuated response to anti-CD3 mAb activation. However, the activity of ERK was equally expressed by T(BM) and T(PBL). It, therefore, appears that the culturing of peripheral T cells with (non-T) BMC anergizes these cells (which become refractory to stimulation through the T-cell receptors), and induces immune suppressor function. These in vitro observations may provide a mechanism by which infused donor BMC serve to downregulate T-cell immunity.

Antigen Presentation↗