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We examined the role of NFκB1 in the homeostasis and function of peripheral follicular (Fo) B cells. Aging mice lacking NFκB1 (Nfκb1(-/-)) develop lymphoproliferative and multiorgan autoimmune disease attributed in large part to the deregulated activity of Nfκb1(-/-)Fo B cells that produce excessive levels of the proinflammatory cytokine interleukin 6 (IL-6). Despite enhanced germinal center (GC) B cell differentiation, the formation of GC structures was severely disrupted in the Nfκb1(-/-)mice. Bone marrow chimeric mice revealed that the Fo B cell-intrinsic loss of NFκB1 led to the spontaneous generation of GC B cells. This was primarily the result of an increase in IL-6 levels, which promotes the differentiation of Fo helper CD4(+)T cells and acts in an autocrine manner to reduce antigen receptor and toll-like receptor activation thresholds in a population of proliferating IgM(+)Nfκb1(-/-)Fo B cells. We demonstrate that p50-NFκB1 represses Il-6 transcription in Fo B cells, with the loss of NFκB1 also resulting in the uncontrolled RELA-driven transcription of Il-6.Collectively, our findings identify a previously unrecognized role for NFκB1 in preventing multiorgan autoimmunity through its negative regulation of Il-6 gene expression in Fo B cells., (© 2016 de Valle et al.)

The mechanistic links between genetic variation and autoantibody production in autoimmune disease remain obscure. Autoimmune lymphoproliferative syndrome (ALPS) is caused by inactivating mutations in FAS or FASL, with autoantibodies thought to arise through failure of FAS-mediated removal of self-reactive germinal center (GC) B cells. Here we show that FAS is in fact not required for this process. Instead, FAS inactivation led to accumulation of a population of unconventional GC B cells that underwent somatic hypermutation, survived despite losing antigen reactivity, and differentiated into a large population of plasma cells that included autoantibody-secreting clones. IgE(+) plasma cell numbers, in particular, increased after FAS inactivation and a major cohort of ALPS-affected patients were found to have hyper-IgE. We propose that these previously unidentified cells, designated "rogue GC B cells," are a major driver of autoantibody production and provide a mechanistic explanation for the linked production of IgE and autoantibodies in autoimmune disease., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Loss of function of the tumor suppressor gene PRDM1 (also known as BLIMP1) or deregulated expression of the oncogene BCL6 occurs in a large proportion of diffuse large B cell lymphoma (DLBCL) cases. However, targeted mutation of either gene in mice leads to only slow and infrequent development of malignant lymphoma, and despite frequent mutation of BCL6 in activated B cells of healthy individuals, lymphoma development is rare. Here we show that T cells prevent the development of overt lymphoma in mice caused by Blimp1 deficiency or overexpression of Bcl6 in the B cell lineage. Impairment of T cell control results in rapid development of DLBCL-like disease, which can be eradicated by polyclonal CD8(+) T cells in a T cell receptor-, CD28- and Fas ligand-dependent manner. Thus, malignant transformation of mature B cells requires mutations that impair intrinsic differentiation processes and permit escape from T cell-mediated tumor surveillance.

Tolerance to self-antigens within the adaptive immune system is safeguarded, at least in part, through deletion of autoreactive T and B lymphocytes. This deletion can occur during the development of these cells in primary lymphoid organs, the thymus or bone marrow, respectively, or at the mature stage in peripheral lymphoid tissues. Deletion of autoreactive lymphocytes is achieved to a large extent through apoptotic cell death. This review describes current understanding of the mechanisms that mediate apoptosis of autoreactive lymphocytes during their development in primary lymphoid organs and during their activation in the periphery. In particular, we discuss the roles of the proapoptotic Bcl-2 family member Bim and the small family of Nur77-related transcriptional regulators in lymphocyte negative selection. Finally, we speculate on the processes that may lead to the activation of Bim when antigen receptors are activated on autoreactive T or B cells.

Immunization with T cell-dependent antigens generates long-lived memory B cells and antibody-forming cells (AFCs). Both populations originate in germinal centers and, predominantly, produce antibodies with high affinity for antigen. The means by which germinal center B cells are recruited into these populations remains unclear. We have examined affinity maturation of antigen-specific B cells in mice expressing the cell death inhibitor bcl-2 as a transgene. Such mice had reduced apoptosis in germinal centers and an excessive number of memory B cells with a low frequency of V gene somatic mutation, including those mutations encoding amino acid exchanges known to enhance affinity. Despite the frequency of AFCs being increased in bcl-2-transgenic mice, the fraction secreting high-affinity antibody in the bone marrow at day 42 remained unchanged compared with controls. The inability of BCL-2 to alter selection of bone marrow AFCs is consistent with these cells being selected within the germinal center on the basis of their affinity being above some threshold rather than their survival being due to a selective competition for an antigen-based signal. Continuous competition for antigen does, however, explain formation of the memory compartment.

Rel and nuclear factor (NF)-kappaB1, two members of the Rel/NF-kappaB transcription factor family, are essential for mitogen-induced B cell proliferation. Using mice with inactivated Rel or NF-kappaB1 genes, we show that these transcription factors differentially regulate cell cycle progression and apoptosis in B lymphocytes. Consistent with an increased rate of mature B cell turnover in naive nfkb1-/- mice, the level of apoptosis in cultures of quiescent nfkb1-/-, but not c-rel-/-, B cells is higher. The failure of c-rel-/- or nfkb1-/- B cells to proliferate in response to particular mitogens coincides with a cell cycle block early in G1 and elevated cell death. Expression of a bcl-2 transgene prevents apoptosis in resting and activated c-rel-/- and nfkb1-/- B cells, but does not overcome the block in cell cycle progression, suggesting that the impaired proliferation is not simply a consequence of apoptosis and that Rel/NF-kappaB proteins regulate cell survival and cell cycle control through independent mechanisms. In contrast to certain B lymphoma cell lines in which mitogen-induced cell death can result from Rel/NF-kappaB-dependent downregulation of c-myc, expression of c-myc is normal in resting and stimulated c-rel-/- B cells, indicating that target gene(s) regulated by Rel that are important for preventing apoptosis may differ in normal and immortalized B cells. Collectively, these results are the first to demonstrate that in normal B cells, NF-kappaB1 regulates survival of cells in G0, whereas mitogenic activation induced by distinct stimuli requires different Rel/NF-kappaB factors to control cell cycle progression and prevent apoptosis.

B lymphocyte differentiation proceeds through a series of alternating stages of proliferative expansion interspersed with noncycling stationary phases during which cells undergo either positive selection or apoptotic cell death. The molecular control of cell cycle progression and that of apoptosis appear to be interconnected. Overexpression of Bcl-2 in lymphocytes or fibroblasts antagonizes apoptosis and delays their transition from the quiescent state into the cell cycle. We have undertaken a systematic analysis of the impact of bcl-2 transgene expression on cell cycle distribution and turnover rate of developing B lymphocytes in normal mice and in mutant animals in which B cell differentiation is arrested at the pro-B/pre-BI or the pre-BII stage. These experiments revealed that overexpression of Bcl-2 reduces proliferation and slows turnover of B cells at all stages of development. This demonstrates that Bcl-2 can retard transition of B cells between the quiescent and the cycling state regardless of the mitogenic stimulus and the differentiation stage. The implications of these results for the normal control of B lymphopoiesis and for lymphomagenesis are discussed.

The non-obese diabetic (NOD) mouse is a good model of insulin-dependent diabetes mellitus. Autoreactive T cells may play a fundamental role in disease initiation in this model, while disregulation of such cells may result from an abnormal thymic microenvironment. Diabetes is prevented in NOD mice by direct introduction of an E alpha d transgene (NOD-E) or a modified I-A beta chain of NOD origin (NOD-PRO or NOD-ASP). To investigate if disease pathology in NOD mice, protection from disease in transgenic NOD-E and NOD-PRO and partial protection from disease in NOD-ASP can be attributed to alterations in the thymic microenvironment, immunohistochemical and flow cytometric analysis of the thymi of these mouse strains was studied. Thymi from NOD and NOD-E mice showed a progressive increase in thymic B-cell percentage from 12 weeks of age. This was accompanied by a concomitant loss in thymic epithelial cells with the appearance of large epithelial-free areas mainly at the corticomedullary junction, which increased in size and number with age and contained the B-cell clusters. Such thymic B cells did not express CD5 and were absent in CBA, NOD-ASP and NOD-PRO mice as were the epithelial cell-free spaces, even at 5 months of age. Therefore the mechanisms of disease protection in the transgenic NOD-E and NOD-ASP/NOD-PRO mice may differ if these thymic abnormalities are related to disease.