Biomedical subjects

Robert C Rickert

Publications and source records attributed to Robert C Rickert.

16 recordsLinked to original sources

PubMed2006

Cutting edge: inherent and acquired resistance to radiation-induced apoptosis in B cells: a pivotal role for STAT3.

Radiation-induced apoptosis (RiA) is used therapeutically for tumor cell ablation as well as a tool to characterize hemopoietic cell lineages. We report that the peritoneal B-1 B cell subset is selectively resistant to RiA. Inherent radioresistance is not shared by splenic B-2 or B-1 cells. However, it is conferred upon B-2 cells by BCR crosslinking in the presence of IL-6 or IL-10. In vivo experiments with gene-targeted mice confirm that IL-6 and, to a lesser extent, IL-10 are the relevant stimuli that combine with BCR ligands to promote B-1 cell radioresistance. STAT3 promotes cell survival in response to selected growth factors, and is activated by combined BCR crosslinking and IL-6 (IL-10). Importantly, STAT3(-/-) B-1 cells become susceptible to irradiation, indicating that STAT3 activation by the BCR in the presence of IL costimuli account for the inherent radioresistance of peritoneal B-1 B cells.

Animals↗

PubMed2006

Regulation of class-switch recombination and plasma cell differentiation by phosphatidylinositol 3-kinase signaling.

Class-switch recombination (CSR) is essential for humoral immunity. However, the regulation of CSR is not completely understood. Here we demonstrate that phosphatidylinositol 3-kinase (PI3K) actively suppressed the onset and frequency of CSR in primary B cells. Consistently, mice lacking the lipid phosphatase, PTEN, in B cells exhibited a hyper-IgM condition due to impaired CSR, which could be restored in vitro by specific inhibition of PI3Kdelta. Inhibition of CSR by PI3K was partially dependent on the transcription factor, BLIMP1, linking plasma cell commitment and cessation of CSR. PI3K-dependent activation of the serine-threonine kinase, Akt, suppressed CSR, in part, through the inactivation of the Forkhead Box family (Foxo) of transcription factors. Reduced PI3K signaling enhanced the expression of AID (activation-induced cytidine deaminase) and accelerated CSR. However, ectopic expression of AID could not fully overcome inhibition of CSR by PI3K, suggesting that PI3K regulates both the expression and function of AID.

Animals↗

PubMed2006

Alternative and classical NF-kappa B signaling retain autoreactive B cells in the splenic marginal zone and result in lupus-like disease.

Expression of B cell-activating factor (BAFF), a critical B cell survival factor, is elevated in autoimmune and lymphoproliferative disorders. Mice overproducing BAFF develop systemic lupus erythematosus (SLE)-like disease and exhibit B cell activation of classical and alternative NF-kappaB-signaling pathways. We used a genetic approach and found that both NF-kappaB-signaling pathways contributed to disease development but act through distinct mechanisms. Whereas BAFF enhanced long-term B cell survival primarily through the alternative, but not the classical, NF-kappaB pathway, it promoted immunoglobulin class switching and generation of pathogenic antibodies through the classical pathway. Activation of the alternative NF-kappaB pathway resulted in integrin upregulation, thereby retaining autoreactive B cells in the splenic marginal zone, a compartment that contributes to their survival. Thus, both classical and alternative NF-kappaB signaling are important for development of lupus-like disease associated with BAFF overproduction. The same mechanisms may be involved in the pathogenesis of human SLE.

Animals↗

PubMed2005

A critical role for complement C3d and the B cell coreceptor (CD19/CD21) complex in the initiation of inflammatory arthritis.

Complement C3 cleavage products mediate the recognition and clearance of toxic or infectious agents. In addition, binding of the C3d fragment to Ag promotes B lymphocyte activation through coengagment of the BCR and complement receptor 2 (CD21). Signal augmentation is thought to be achieved through enhanced recruitment and activation of CD21-associated CD19. In this study we show, using the DBA/1 collagen-induced arthritis (CIA) model, that conjugation of C3d to heterologous type II collagen is sufficient to cause disease in the absence of the mycobacterial components of CFA. Transient depletion of C3 during the inductive phase of CIA delays and lessens the severity of disease, and DBA/1 mice deficient for coreceptor components CD19 or CD21 are not susceptible to CIA. Adoptive transfer experiments revealed that CD21 expression on either B cells or follicular dendritic cells is sufficient to acquire disease susceptibility. Although CD19(-/-) and CD21(-/-) mice produce primary Ab responses to heterologous and autologous type II collagen, they are impaired in the ability to activate T cells, form germinal centers, and produce secondary autoantibody responses. These findings indicate that binding of C3d to self-Ags can promote autoimmunity through enhanced Ag retention and presentation by follicular dendritic cells and B cells, respectively.

Animals↗

PubMed2005

Critical role for Stat3 in T-dependent terminal differentiation of IgG B cells.

Stat proteins are latent cytoplasmic transcription factors that are crucial in many aspects of mammalian development. In the immune system, Stat3 has distinct roles in T-cell, neutrophil, and macrophage function, but a role for Stat3 in B-cell development, particularly in the terminal differentiation of B cells into antibody-secreting plasma cells, has never been directly tested. In this study, we used the Cre/lox system to generate a mouse strain in which Stat3 was conditionally deleted in the B-cell lineage (Stat3(fl/fl)CD19(Cre/+)). B-cell development, establishment of the peripheral B-cell compartment, and baseline serum antibody levels were unperturbed in Stat3(fl/fl)CD19(Cre/+) mice. Strikingly, Stat3(fl/fl)CD19(Cre/+) mice displayed profound defects in T-dependent (TD) IgG responses, but normal TD IgM, IgE, and IgA responses and T-independent (TI) IgM and IgG3 responses. In addition, germinal center (GC) formation, isotype switching, and generation of memory B cells, including IgG+ memory cells, were all intact in Stat3(fl/fl)CD19(Cre/+) mice, indicating that the requirement for Stat3 was limited to plasma cell differentiation. These results demonstrate a profound yet highly selective role for Stat3 in TD IgG plasma cell differentiation, and therefore represent a unique example of a transcription factor regulating isotype-specific terminal B-cell differentiation.

Animals↗

PubMed2005

Regulation of B lymphocyte activation by complement C3 and the B cell coreceptor complex.

Complement is an essential innate immune mechanism that recognizes and eradicates microbes and associated toxins. In addition, complement receptors (CD21 and CD35) on B cells cooperate with the B-cell antigen receptor (BCR) to efficiently recognize and respond to antigens bearing complement C3d(g). Fixation of C3d(g) to antigen confers adjuvant properties and therefore its deposition may need to be carefully regulated to avoid autoreactivity. CD21 and/or CD35 engagement is nonmitogenic, and B-cell activation via BCR-CD21 coligation is enhanced through the recruitment of CD19. Recent efforts have sought a better understanding of the topological and biochemical properties of BCR and coreceptor (CD19-CD21-CD81) signaling, as well as the context for complement activation in the response to foreign and self antigens.

Animals↗

PubMed2005

CD19 function in central and peripheral B-cell development.

Although the B-cell antigen receptor (BCR) factors most prominently in the maintenance and differentiation of mature B cells, it is now appreciated that co-receptor molecules can positively or negatively modulate signals through the BCR. Co-receptors are functionally defined as modifiers of BCR engagement and signal transduction, and are distinct from other accessory molecules that act independently to regulate B-cell growth. The co-receptor CD19 functions to augment signals by the pre-BCR/BCR and in doing so can modulate B-cell fate decisions at multiple stages of development. In mature B cells, CD19 also associates with complement receptor 2 (CR2/CD21) and is pivotal for transducing signals induced by co-recognition of complement C3d-fixed antigens by the BCR and CD21. In this article, we focus on recent progress in the understanding of CD19 function through the characterization of mouse models that relate in vivo function to biochemical properties of CD19.

Animals↗

PubMed2004

Activation of IKKalpha target genes depends on recognition of specific kappaB binding sites by RelB:p52 dimers.

IkappaB Kinase (IKK)alpha is required for activation of an alternative NF-kappaB signaling pathway based on processing of the NF-kappaB2/p100 precursor protein, which associates with RelB in the cytoplasm. This pathway, which activates RelB:p52 dimers, is required for induction of several chemokine genes needed for organization of secondary lymphoid organs. We investigated the basis for the IKKalpha dependence of the induction of these genes in response to engagement of the lymphotoxin beta receptor (LTbetaR). Using chromatin immunoprecipitation, we found that the promoters of organogenic chemokine genes are recognized by RelB:p52 dimers and not by RelA:p50 dimers, the ubiquitous target for the classical NF-kappaB signaling pathway. We identified in the IKKalpha-dependent promoters a novel type of NF-kappaB-binding site that is preferentially recognized by RelB:p52 dimers. This site links induction of organogenic chemokines and other important regulatory molecules to activation of the alternative pathway.

Adaptor Proteins, Signal Transducing↗

PubMed2004

Act1, a negative regulator in CD40- and BAFF-mediated B cell survival.

TNF receptor (TNFR) superfamily members, CD40, and BAFFR play critical roles in B cell survival and differentiation. Genetic deficiency in a novel adaptor molecule, Act1, for CD40 and BAFF results in a dramatic increase in peripheral B cells, which culminates in lymphadenopathy and splenomegaly, hypergammaglobulinemia, and autoantibodies. While the B cell-specific Act1 knockout mice displayed a similar phenotype with less severity, the pathology of the Act1-deficient mice was mostly blocked in CD40-Act1 and BAFF-Act1 double knockout mice. CD40- and BAFF-mediated survival is significantly increased in Act1-deficent B cells, with stronger IkappaB phosphorylation, processing of NF-kappaB2 (p100/p52), and activation of JNK, ERK, and p38 pathways, indicating that Act1 negatively regulates CD40- and BAFF-mediated signaling events. These findings demonstrate that Act1 plays an important role in the homeostasis of B cells by attenuating CD40 and BAFFR signaling.

Animals↗

PubMed2004

Genetic dissection of antigen receptor induced-NF-kappaB activation.

NF-kappaB is a master transcription factor in the immune system. It regulates various aspects of immune cell development, homeostasis, survival and function. It is in these contexts that the signaling pathways leading to NF-kappaB activation are best understood. This review addresses the cell signaling from antigen receptors as well as Toll-like receptors to NF-kappaB in both innate and adaptive immunity as revealed by the analysis of mice lacking specific signaling intermediates.

Animals↗

PubMed2003

CD19 function in early and late B cell development. II. CD19 facilitates the pro-B/pre-B transition.

Proliferative expansion of pro-B cells is an IL-7-dependent process that allows for the rearrangement of H chain genes and the expression of the pre-B cell receptor (pre-BCR). Further B cell differentiation is dependent upon signals elicited through the pre-BCR, which are thought to be responsible for allelic exclusion, induced L chain gene rearrangement, and continued proliferation. CD19 promotes the proliferation and survival of mature B cells, but its role in early B cell development is less well understood. Here we identify and characterize impairments in early B cell development in CD19(-/-) mice. Following sublethal irradiation, we found decreased numbers of autoreconstituted early B cells, which was first evident in the large cycling pre-B cell fraction. Reduced cell progression due to a defect in proliferation was made evident from cell cycle analysis and bromodeoxyuridine labeling of bone marrow cells from CD19(-/-) and wild-type mice. Studies of IL-7-dependent pre-B cell cultures derived from wild-type and CD19(-/-) mouse bone marrow suggested that CD19 has little affect on IL-7 signaling. By contrast, signaling through the pre-BCR was impaired in the absence of CD19, as demonstrated by reduced activation of Bruton's tyrosine kinase and extracellular signal-regulated kinase/mitogen-activated protein kinase. Thus, in addition to promoting mature B cell homeostasis and Ag-induced responses, the early onset of CD19 expression acts to enhance B cell generation.

Animals↗

PubMed2003

IKK beta is required for peripheral B cell survival and proliferation.

NF-kappaB activity in mammalian cells is regulated through the IkappaB kinase (IKK) complex, consisting of two catalytic subunits (IKKalpha and IKKbeta) and a regulatory subunit (IKKgamma). Targeted deletion of Ikkbeta results in early embryonic lethality, thus complicating the examination of IKKbeta function in adult tissues. Here we describe the role of IKKbeta in B lymphocytes made possible by generation of a mouse strain that expresses a conditional Ikkbeta allele. We find that the loss of IKKbeta results in a dramatic reduction in all peripheral B cell subsets due to associated defects in cell survival. IKKbeta-deficient B cells are also impaired in mitogenic responses to LPS, anti-CD40, and anti-IgM, indicating a general defect in the ability to activate the canonical NF-kappaB signaling pathway. These findings are consistent with a failure to mount effective Ab responses to T cell-dependent and independent Ags. Thus, IKKbeta provides a requisite role in B cell activation and maintenance and thus is a key determinant of humoral immunity.

Animals↗

PubMed2003

Pten inactivation alters peripheral B lymphocyte fate and reconstitutes CD19 function.

Phosphoinositide 3-kinase (PI3K) and phosphatase and tensin homolog (PTEN) phosphatase serve essential functions in the regulation of cell growth, differentiation and survival by modulating intracellular phosphatidylinositol-3,4,5-trisphosphate (PI-3,4,5-P3) concentrations. Here we show that the conditional deletion of Pten in B cells led to the preferential generation of marginal zone (MZ) B cells and B1 cells. PTEN-deficient B cells were hyperproliferative in response to mitogenic stimuli, and exhibited a lower threshold for activation through the B cell antigen receptor. Inactivation of PTEN rescued germinal center, MZ B and B1 cell formation in CD19-/- mice, arguing that recruitment and activation of PI3K are the dominant roles for CD19 in these B cell subpopulations. These findings establish the central role of PI-3,4,5-P3 regulation in the differentiation of peripheral B cell subsets.

Animals↗

PubMed2003

CD19 function in early and late B cell development: I. Maintenance of follicular and marginal zone B cells requires CD19-dependent survival signals.

Loss of membrane-bound Ig results in the rapid onset of apoptosis in recirculating B cells. This observation implies that a competent B cell receptor (BCR) is not only required for Ag-dependent differentiation, but also for continued survival in the peripheral immune system. Expression of the B cell coreceptor, CD19, is likewise essential for key B cell differentiative events including the formation of B-1, germinal center, and marginal zone (MZ) B cells. In this study, we report that CD19 also exerts a role before Ag encounter by promoting the survival of naive recirculating B cells. This aspect of CD19 signaling was first suggested by the analysis of mixed bone marrow chimeras, wherein CD19-/- B cells fail to effectively compete with wild-type B cells to reconstitute the peripheral B cell compartment. Consistent with this observation, Bromodeoxyuridine- and CFSE-labeling studies reveal a shorter in vivo life span for CD19-/- B cells vs their wild-type counterparts. Moreover, we find that CD19 is necessary for propagation of BCR-induced survival signals and thus may contribute to homeostatic mechanisms of tonic signaling. To determine whether provision of a constitutive survival signal could compensate for the loss of CD19 in vivo, Bcl-2-transgenic mice were bred onto the CD19-/- background. Here, we observe an increase in follicular B cell numbers and selective recovery of the MZ B cell compartment. Together these findings suggest that maintenance of the follicular and MZ B cell compartments require CD19-dependent survival signals.

Adoptive Transfer↗

PubMed2003

Hypoxia-inducible factor 1alpha is essential for cell cycle arrest during hypoxia.

A classical cellular response to hypoxia is a cessation of growth. Hypoxia-induced growth arrest differs in different cell types but is likely an essential aspect of the response to wounding and injury. An important component of the hypoxic response is the activation of the hypoxia-inducible factor 1 (HIF-1) transcription factor. Although this transcription factor is essential for adaptation to low oxygen levels, the mechanisms through which it influences cell cycle arrest, including the degree to which it cooperates with the tumor suppressor protein p53, remain poorly understood. To determine broadly relevant aspects of HIF-1 function in primary cell growth arrest, we examined two different primary differentiated cell types which contained a deletable allele of the oxygen-sensitive component of HIF-1, the HIF-1alpha gene product. The two cell types were murine embryonic fibroblasts and splenic B lymphocytes; to determine how the function of HIF-1alpha influenced p53, we also created double-knockout (HIF-1alpha null, p53 null) strains and cells. In both cell types, loss of HIF-1alpha abolished hypoxia-induced growth arrest and did this in a p53-independent fashion. Surprisingly, in all cases, cells lacking both p53 and HIF-1alpha genes have completely lost the ability to alter the cell cycle in response to hypoxia. In addition, we have found that the loss of HIF-1alpha causes an increased progression into S phase during hypoxia, rather than a growth arrest. We show that hypoxia causes a HIF-1alpha-dependent increase in the expression of the cyclin-dependent kinase inhibitors p21 and p27; we also find that hypophosphorylation of retinoblastoma protein in hypoxia is HIF-1alpha dependent. These data demonstrate that the transcription factor HIF-1 is a major regulator of cell cycle arrest in primary cells during hypoxia.

Animals↗

PubMed2002

The physiologic role of CD19 cytoplasmic tyrosines.

The physiologic role of eight CD19 tyrosines was examined in CD19-knockout mice expressing transgenic CD19 constructs. CD19 Y482 and Y513 were essential for normal B cell biology, including differentiation of B1 and marginal zone B cells and for T-dependent and -independent antibody responses. In immunized mice with mutations in CD19 Y482 and Y513, early germinal center B cells appeared normal in phenotype and number, but maturation in the germinal center was defective. This was associated with retarded progression through the cell cycle. Thus, Y482 and Y513 are essential for all functions of CD19 in vivo. Mutation of these reduces proliferation in germinal center B cells, providing a potential mechanism for the failure of maturation, which abrogates antibody responses.

Animals↗