The anti-apoptotic activities of Rel and RelA required during B-cell maturation involve the regulation of Bcl-2 expression.
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Rel and RelA, individually dispensable for lymphopoiesis, serve unique functions in activated B and T cells. Here their combined roles in lymphocyte development were examined in chimeric mice repopulated with c-rel(-/-) rela(-/-) fetal liver hemopoietic stem cells. Mice engrafted with double-mutant cells lacked mature IgM(lo)IgD(hi) B cells, and numbers of peripheral CD4(+) and CD8(+) T cells were markedly reduced. The absence of mature B cells was associated with impaired survival that coincided with reduced expression of bcl-2 and A1. bcl-2 transgene expression not only prevented apoptosis and increased peripheral B-cell numbers, but also induced further maturation to an IgM(lo)IgD(hi) phenotype. In contrast, the survival of double-mutant T cells was normal and the bcl-2 transgene could not rectify the peripheral T-cell deficit. These findings indicate that Rel and RelA serve essential, albeit redundant, functions during the later antigen-independent stages of B- and T-cell maturation, with these transcription factors promoting the survival of peripheral B cells in part by upregulating Bcl-2. (+info)
Severe B cell deficiency in mice lacking the tec kinase family members Tec and Btk.
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The cytoplasmic protein tyrosine kinase Tec has been proposed to have important functions in hematopoiesis and lymphocyte signal transduction. Here we show that Tec-deficient mice developed normally and had no major phenotypic alterations of the immune system. To reveal potential compensatory roles of other Tec kinases such as Bruton's tyrosine kinase (Btk), Tec/Btk double-deficient mice were generated. These mice exhibited a block at the B220(+)CD43(+) stage of B cell development and displayed a severe reduction of peripheral B cell numbers, particularly immunoglobulin (Ig)M(lo)IgD(hi) B cells. Although Tec/Btk(null) mice were able to form germinal centers, the response to T cell-dependent antigens was impaired. Thus, Tec and Btk together have an important role both during B cell development and in the generation and/or function of the peripheral B cell pool. The ability of Tec to compensate for Btk may also explain phenotypic differences in X-linked immunodeficiency (xid) mice compared with human X-linked agammaglobulinemia (XLA) patients. (+info)
Natural autoantibodies against heat-shock proteins hsp70 and gp96: implications for immunotherapy using heat-shock proteins.
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Immunization of mice with cognate cancer-derived heat-shock protein (hsp) preparations leads to protection from cancer growth. As hsp used for vaccination or therapy are derived from autologous cancers, questions of pathological autoimmunity are of immense significance for the ongoing translation of this approach to therapy of human cancer. Employing the sera of normal adult mice as the first antibody, highly sensitive immunoblotting revealed the presence of anti-hsp natural autoantibodies in healthy animals. Natural autoantibodies of the immunoglobulin D (IgD) isotype bind to gp96, whereas hsp70 was recognized by IgD and IgM autoantibodies. Neither hsp was recognized by the IgA, IgE or IgG immunoglobulins contained in the serum. The antigen-antibody recognition was titratable and dependent on the integrity of the IgD molecule. Sera from only a subset of the animals tested were found to be positive for autoantibodies against gp96 and hsp70, and individual and strain-specific variations were detected. Injection of gp96 into healthy mice did not show sustained or consistent anti-gp96 IgD antibody response, class switching, toxicity or pathological autoimmunity. IgD autoantibodies against gp96 and hsp70 were also not detected in the autoimmune lpr mice. These observations show the existence of a measured and tightly regulated natural immune response to hsp. (+info)
Biochemical and genetic aspects of mevalonate kinase and its deficiency.
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Mevalonate kinase (MK) is an essential enzyme in the mevalonate pathway which produces numerous cellular isoprenoids. The enzyme has been characterized both at the biochemical and the molecular level in a variety of organisms. Despite the fact that mevalonate kinase is not the rate-limiting enzyme in isoprenoid biosynthesis, its activity is subject to feedback regulation by the branch-point intermediates geranyldiphosphate, farnesyldiphosphate and geranylgeranyldiphosphate. Recently, the importance of mevalonate kinase was demonstrated by the identification of its deficiency as the biochemical and molecular cause of the inherited human disorders mevalonic aciduria and hyperimmunoglobulinemia D and periodic fever syndrome. The pathophysiology of these disorders is not yet understood, but eventually will give insight into the in vivo role of mevalonate kinase and isoprenoid biosynthesis with respect to the acute phase response and fever. The subcellular localization of mevalonate kinase is still a matter of debate. The enzyme could be localized predominantly in the cytosol, or in peroxisomes, or it is associated differentially with peroxisomes. Here we review the biochemical and molecular properties of MK, and discuss its biological significance, the regulation of its enzyme activity and finally its subcellular localization. (+info)
RAG1 and RAG2 expression by B cell subsets from human tonsil and peripheral blood.
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It has been suggested that B cells acquire the capacity for secondary V(D)J recombination during germinal center (GC) reactions. The nature of these B cells remains controversial. Subsets of tonsil and blood B cells and also individual B cells were examined for the expression of recombination-activating gene (RAG) mRNA. Semiquantitative analysis indicated that RAG1 mRNA was present in all tonsil B cell subsets, with the largest amount found in naive B cells. RAG2 mRNA was only found in tonsil naive B cells, centrocytes, and to a lesser extent in centroblasts. Neither RAG1 nor RAG2 mRNA was routinely found in normal peripheral blood B cells. In individual tonsil B cells, RAG1 and RAG2 mRNAs were found in 18% of naive B cells, 22% of GC founder cells, 0% of centroblasts, 13% of centrocytes, and 9% of memory B cells. Individual naive tonsil B cells containing both RAG1 and RAG2 mRNA were activated (CD69(+)). In normal peripheral blood approximately 5% of B cells expressed both RAG1 and RAG2. These cells were uniformly postswitch memory B cells as documented by the coexpression of IgG mRNA. These results indicate that coordinate RAG expression is not found in normal peripheral naive B cells but is up-regulated in naive B cells which are activated in the tonsil. With the exception of centroblasts, RAG1 and RAG2 expression can be found in all components of the GC, including postswitch memory B cells, some of which may circulate in the blood of normal subjects. (+info)
Expression of alpha4beta7 and E-selectin ligand by circulating memory B cells: implications for targeted trafficking to mucosal and systemic sites.
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We have examined the expression of homing receptors on circulating memory B cells subsets. Blood IgD+ (naive) B cells homogeneously express a high level of intestinal homing receptor, alpha4beta7, but IgD- (putative memory) B cells comprise distinct alpha4beta7+ and alpha4beta7- subsets. Naive and alpha4beta7+ memory B cells but not alpha4beta7- cells bind MAdCAM-1, suggesting that alpha4beta7 expression may predict B cell intestinal homing. In contrast, alpha4beta7+ and alpha4beta7- B cells bind well to VCAM-1, possibly allowing recruitment of both subsets to extra-intestinal sites, including those tissues of the "common mucosal immune system" characterized by vascular VCAM-1 expression. sIgA+ B cells, which are associated with mucosal immunity in the gut and elsewhere, are heterogeneous in homing receptor expression--with discrete subsets expressing alpha4beta7, L-selectin, and cutaneous lymphocyte antigen (CLA). sIgA+ CLA+ B cells are enriched by binding to E-selectin, suggesting that CLA may participate in B cell homing to nonintestinal mucosal tissues characterized by vascular E-selectin expression, such as chronically inflamed bronchial or oral mucosal. We conclude that circulating human peripheral blood memory B cells, like T cells, consist of discrete homing receptor-defined subsets. This diversity in homing phenotypes is apparent even among sIgA (presumptive mucosal) memory B cells, implying heterogeneity in trafficking mechanisms to different target mucosal surfaces. (+info)
B cell development is arrested at the immature B cell stage in mice carrying a mutation in the cytoplasmic domain of immunoglobulin beta.
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The B cell receptor (BCR) regulates B cell development and function through immunoglobulin (Ig)alpha and Ig beta, a pair of membrane-bound Ig superfamily proteins, each of which contains a single cytoplasmic immunoreceptor tyrosine activation motif (ITAM). To determine the function of Ig beta, we produced mice that carry a deletion of the cytoplasmic domain of Ig beta (Ig beta Delta C mice) and compared them to mice that carry a similar mutation in Ig alpha (MB1 Delta C, herein referred to as Ig alpha Delta C mice). Ig beta Delta C mice differ from Ig alpha Delta C mice in that they show little impairment in early B cell development and they produce immature B cells that respond normally to BCR cross-linking as determined by Ca(2+) flux. However, Ig beta Delta C B cells are arrested at the immature stage of B cell development in the bone marrow and die by apoptosis. We conclude that the cytoplasmic domain Ig beta is required for B cell development beyond the immature B cell stage and that Ig alpha and Ig beta have distinct biologic activities in vivo. (+info)
Hyper-immunoglobulin A in the hyperimmunoglobulinemia D syndrome.
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The hyperimmunoglobulinemia D syndrome (HIDS) is an autosomal recessive disorder characterized by recurrent febrile attacks with abdominal, articular, and skin manifestations. Apart from elevated immunoglobulin D (IgD) levels (>100 IU/ml), there are high IgA levels in the majority of cases. Mutations in the gene encoding mevalonate kinase constitute the molecular defect in HIDS. The cause of elevated IgA concentrations in HIDS patients remains to be elucidated. We studied the hyper-IgA response in serum of a group of HIDS patients. Elevated IgA concentrations result from increased IgA1 concentrations. IgA and IgA1 concentrations correlated significantly with IgD concentrations, and levels of IgA polymers were significantly higher than the levels in healthy donors. These results indicate a continuous, presumably systemic, stimulation of IgA in HIDS patients. (+info)