Dianne Emslie

B and T cells collaborate in antiviral responses via IL-6, IL-21, and transcriptional activator and coactivator, Oct2 and OBF-1

Transcriptional activator Oct2 and cofactor OBF-1 regulate B cell IL-6 to induce T cell production of IL-21, to support Tfh cell development in antiviral immunity.

Normalization of boutique two-color microarrays with a high proportion of differentially expressed probes.

Normalization is critical for removing systematic variation from microarray data. For two-color microarray platforms, intensity-dependent lowess normalization is commonly used to correct relative gene expression values for biases. Here we outline a normalization method for use when the assumptions of lowess normalization fail. Specifically, this can occur when specialized boutique arrays are constructed that contain a subset of genes selected to test particular biological functions.

The transcription factors IRF8 and PU.1 negatively regulate plasma cell differentiation

Carotta et al. show that the interaction between IRF8 and PU.1 controls the propensity of B cells to undergo class-switch recombination and plasma cell differentiation by concurrently promoting the expression of BCL6 and PAX5 and repressing AID and BLIMP-1.

Oct2 enhances antibody-secreting cell differentiation through regulation of IL-5 receptor α chain expression on activated B cells

Mice lacking a functional gene for the Oct2 transcriptional activator display several developmental and functional deficiencies in the B lymphocyte lineage. These include defective B cell receptor (BCR) and Toll-like receptor 4 signaling, an absence of B-1 and marginal zone populations, and globally reduced levels of serum immunoglobulin (Ig) in naive and immunized animals. Oct2 was originally identified through its ability to bind to regulatory regions in the Ig loci, but genetic evidence has not supported an essential role for Oct2 in the expression of Ig genes. We describe a new Oct2-mediated role in B cells. Oct2 augments the ability of activated B cells to differentiate to antibody-secreting plasma cells (ASCs) under T cell–dependent conditions through direct regulation of the gene encoding the α chain of the interleukin (IL) 5 receptor. Ectopic expression of IL-5Rα in oct2-deficient B cells largely restores their ability to differentiate to functional ASCs in vitro but does not correct other phenotypic defects in the mutants, such as the maturation and specialization of peripheral B cells, which must therefore rely on distinct Oct2 target genes. IL-5 augments ASC differentiation in vitro, and we show that IL-5 directly activates the plasma cell differentiation program by enhancing blimp1 expression.

The BTB-ZF transcription factor Zbtb20 is driven by Irf4 to promote plasma cell differentiation and longevity

Zbtb20 facilitates terminal differentiation of B cells into antibody-secreting cells, and its expression is dependent on Irf4 and independent of Blimp1.

Blimp1 is limiting for transformation in a mouse plasmacytoma model

Multiple myeloma (MM) and plasmacytomas are cancers of antibody-secreting cells (ASCs). PRDM1/BLIMP1 is an essential regulator of ASC development. Histologic evidence shows that 100% of MM expresses PRDM1/BLIMP1, indicating that PRDM1/BLIMP1 is important for the development or persistence of MM. In contrast, some diffuse large B-cell lymphomas (DLBCLs) lose PRDM1 expression, suggesting that PRDM1 may act as a tumor suppressor in DLBCL. Thus, the role of PRDM1/BLIMP1 in transformation of mature B cells is unclear. We have used a plasmacytoma-prone transgenic mouse model to study the effect of Blimp1 loss on plasmacytoma prevalence, latency, and phenotype. Two possible outcomes could be envisaged: loss of Blimp1 might decrease plasmacytoma prevalence, through reduction of plasma cells, and so the number of susceptible transformation targets. Alternatively, Blimp1 may participate in the transformation process itself. Our results support the latter scenario, showing that decreasing Blimp1 dosage does not change plasma cell number in nontransgenic mice in vivo, but it significantly reduces plasmacytoma prevalence in transgenic mice. Loss of functional Blimp1 completely prevents plasmacytoma formation in this tumor model. These observations suggest that Blimp1 is limiting for plasma cell transformation and thus has potential as a target for new therapies to combat MM.

Germinal center-independent, IgM-mediated autoimmunity in sanroque mice lacking Obf1.

Mice homozygous for a point mutation in the Rc3h1 gene encoding Roquin1, designated sanroque mice, develop a severe antibody‐mediated autoimmune condition. The disease is T‐cell intrinsic, exacerbated by macrophage‐intrinsic defects and driven by excessive T follicular helper cell generation and spontaneous germinal centre (GC) formation. This culminates in abnormally high numbers of plasma cells secreting high‐affinity autoreactive immunoglobulin G (IgG). Obf1 is a transcriptional co‐activator required for normal T‐cell‐dependent antibody responses, and it is essential for GC formation under all circumstances so far tested. We crossed sanroque mice with Obf1‐null mice to determine whether the hyperactivity of sanroque T cells could drive Obf1−/− B cells to differentiate to GC B cells, or conversely, if Obf1 loss would prevent sanroque‐mediated autoimmune disease. Surprisingly, while sanroque/Obf1−/− mice did not form GC, they still developed autoimmune disease and succumbed even more rapidly than did sanroque mice. The disease was mediated by autoreactive IgM, which may have been derived from a pre‐existing population of autoreactive B cells in the Obf1−/− mice responding to the over‐exuberant activity of sanroque CD4 cells.

Oct2 and Obf1 as Facilitators of B:T Cell Collaboration during a Humoral Immune Response

The Oct2 protein, encoded by the Pou2f2 gene, was originally predicted to act as a DNA binding transcriptional activator of immunoglobulin (Ig) in B lineage cells. This prediction flowed from the earlier observation that an 8-bp sequence, the “octamer motif,” was a highly conserved component of most Ig gene promoters and enhancers, and evidence from over-expression and reporter assays confirmed Oct2-mediated, octamer-dependent gene expression. Complexity was added to the story when Oct1, an independently encoded protein, ubiquitously expressed from the Pou2f1 gene, was characterized and found to bind to the octamer motif with almost identical specificity, and later, when the co-activator Obf1 (OCA-B, Bob.1), encoded by the Pou2af1 gene, was cloned. Obf1 joins Oct2 (and Oct1) on the DNA of a subset of octamer motifs to enhance their transactivation strength. While these proteins variously carried the mantle of determinants of Ig gene expression in B cells for many years, such a role has not been borne out for them by characterization of mice lacking functional copies of the genes, either as single or as compound mutants. Instead, we and others have shown that Oct2 and Obf1 are required for B cells to mature fully in vivo, for B cells to respond to the T cell cytokines IL5 and IL4, and for B cells to produce IL6 normally during a T cell dependent immune response. We show here that Oct2 affects Syk gene expression, thus influencing B cell receptor signaling, and that Oct2 loss blocks Slamf1 expression in vivo as a result of incomplete B cell maturation. Upon IL4 signaling, Stat6 up-regulates Obf1, indirectly via Xbp1, to enable plasma cell differentiation. Thus, Oct2 and Obf1 enable B cells to respond normally to antigen receptor signals, to express surface receptors that mediate physical interaction with T cells, or to produce and respond to cytokines that are critical drivers of B cell and T cell differentiation during a humoral immune response.

IL4 and IL21 cooperate to induce the high Bcl6 protein level required for germinal center formation

Bcl6 (B‐cell lymphoma 6) is a transcriptional repressor and critical mediator of the germinal center reaction during a T‐cell‐dependent antibody response, where it enables somatic hypermutation of immunoglobulin genes and inhibits terminal differentiation via repression of Blimp1. It can also contribute to the development of diffuse large B‐cell lymphoma when expressed inappropriately. Bcl6 regulation is mediated both at the transcriptional and post‐transcriptional levels, and in particular a strong signal through the B‐cell receptor causes rapid proteasomal degradation of Bcl6. Despite the importance of Bcl6 in both immunity and cancer, little is known about how other extrinsic factors regulate Bcl6 in B cells. Here we show that Bcl6 is indeed highly unstable in B cells after a B‐cell receptor (BCR) signal, but that the T‐cell‐derived cytokines interleukin 4 (IL4) and IL21 counteract BCR‐mediated degradation, preserving Bcl6 protein levels. Stat6, downstream of IL4, can induce Bcl6 transcription directly. In vivo, B‐cell intrinsic loss of IL4 or IL21 signaling reduces the magnitude or duration of the GC response, respectively, while their combined loss almost completely eliminates the GC response. This work provides key insights into the effect mediated by T‐follicular helper cytokines on Bcl6 regulation.

Oct2 enhances antibody-secreting cell differentiation through regulation of IL-5 receptor a chain expression on activated B cells

Emslie et al. 2008. J. Exp. Med. doi:10.1084/jem.20072049[OpenUrl][1][Abstract/FREE Full Text][2] [1]: {openurl}?query=rft.jtitle%253DJ.%2BExp.%2BMed.%26rft_id%253Dinfo%253Adoi%252F10.1084%252Fjem.20072049%26rft_id%253Dinfo%253Apmid%252F18250192%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%