IRF4 – a factor for class switching and antibody secretion

Long-Lived Plasma Cells in Mice and Men

Even though more than 30 years have passed since the eradication of smallpox, high titers of smallpox-specific antibodies are still detected in the blood of subjects vaccinated in childhood. In fact, smallpox-specific antibody levels are maintained in serum for more than 70 years. The generation of life-long immunity against infectious diseases such as smallpox and measles has been thoroughly documented. Although the mechanisms behind high persisting antibody titers in the absence of the causative agent are still unclear, long lived plasma cells (LLPCs) play an important role. Most of the current knowledge on LLPCs is based on experiments performed in mouse models, although the amount of data derived from human studies is increasing. As the results from mouse models are often directly extrapolated to humans, it is important to keep in mind that there are differences. These are not only the obvious such as the life span but there are also anatomical differences, for instance the adiposity of the bone marrow (BM) where LLPCs reside. Whether these differences have an effect on the function of the immune system, and in particular on LLPCs, are still unknown. In this review, we will briefly discuss current knowledge of LLPCs, comparing mice and humans.

Cutting Edge: The Transcription Factor Sox2 Regulates AID Expression in Class-Switched B Cells

IgH class switch recombination (CSR) occurs through the deliberate introduction of activation-induced cytidine deaminase (AID)-instigated DNA double-strand breaks into the IgH loci. Because double-strand breaks are generally highly toxic, mechanisms that regulate AID expression are of much relevance to CSR and genomic integrity; however, effectors of such regulatory processes are still poorly understood. In this article, we show that the transcription factor sex determining region Y-box 2 (Sox2) is expressed in activated B cells, but almost exclusively in those that have undergone CSR. We demonstrate that enforced expression of Sox2 in splenic B cells severely inhibits AID expression and CSR, whereas deletion of Sox2 increases the frequency of IgH:c-Myc translocations. These results suggest that Sox2 may regulate AID expression in class-switched B cells to suppress genomic instability associated with CSR.

Fine tuning of IRF-4 expression by SWAP-70 controls the initiation of plasma cell development

The generation of plasma cells (PCs) is key for proper humoral immune responses. The transcription factors IRF-4 and BLIMP-1 (B-lymphocyte induce maturation protein-1) control PC commitment, but the underlying regulatory mechanisms are incompletely understood. Here we have identified SWAP-70 as being critically involved in Toll-like receptor (TLR)-triggered PC differentiation. Upon activation through various TLRs, Swap-70(-/-) B cells were activated and proliferated normally. However, expression of BLIMP-1 was markedly reduced and PC differentiation was impaired. Four hours of LPS stimulation were sufficient to drive PC differentiation, and SWAP-70 was required during this initial period. Swap-70(-/-) B cells pre-activated in vitro failed to efficiently differentiate into PCs upon adoptive transfer into recipient mice. Re-introduction of SWAP-70 into Swap-70(-/-) B cells rescued their development into PCs, and SWAP-70 over-expression in wild-type (WT) B cells increased PC generation. In the absence of SWAP-70, IRF-4 protein levels were reduced and the IRF-4(high) B220(+) CD138(-) compartment, including PC precursors, was strongly diminished. Ectopic expression of SWAP-70 increases IRF-4 protein levels and PC differentiation in WT and Swap-70(-/-) B cells, and IRF-4 over-expression in Swap-70(-/-) B cells elevates PC differentiation to WT levels. Thus, in a dose-dependent manner, SWAP-70 controls IRF-4 protein expression and thereby regulates the initiation of PC differentiation.

Molecular characterization of in vivo adjuvant activity in ferrets vaccinated against influenza virus

The 2009 H1N1 influenza pandemic has prompted a significant need for the development of efficient, single-dose, adjuvanted vaccines. Here we investigated the adjuvant potential of CpG oligodeoxynucleotide (ODN) when used with a human seasonal influenza virus vaccine in ferrets. We found that the CpG ODN-adjuvanted vaccine effectively increased antibody production and activated type I interferon (IFN) responses compared to vaccine alone. Based on these findings, pegylated IFN-alpha2b (PEG-IFN) was also evaluated as an adjuvant in comparison to CpG ODN and complete Freund's adjuvant (CFA). Our results showed that all three vaccines with adjuvant added prevented seasonal human A/Brisbane/59/2007 (H1N1) virus replication more effectively than did vaccine alone. Gene expression profiles indicated that, as well as upregulating IFN-stimulated genes (ISGs), CpG ODN enhanced B-cell activation and increased Toll-like receptor 4 (TLR4) and IFN regulatory factor 4 (IRF4) expression, whereas PEG-IFN augmented adaptive immunity by inducing major histocompatibility complex (MHC) transcription and Ras signaling. In contrast, the use of CFA as an adjuvant induced limited ISG expression but increased the transcription of MHC, cell adhesion molecules, and B-cell activation markers. Taken together, our results better characterize the specific molecular pathways leading to adjuvant activity in different adjuvant-mediated influenza virus vaccinations.

Relationship between interferon regulatory factor 4 genetic polymorphisms, measures of sun sensitivity and risk for non-Hodgkin lymphoma

Objective

Sun exposure and sensitivity, including pigmentation, are associated with risk for non-Hodgkin lymphoma (NHL). One variant in the immune regulatory factor 4 (IRF4) gene (rs12203592) is associated with pigmentation, and a different IRF4 variant (rs12211228) is associated with NHL risk. We evaluated the independent roles of these IRF4 polymorphisms and sun sensitivity in mediating NHL risk and explored whether they are confounded or modified by each other.

Methods

Genotyping of tag single nucleotide polymorphisms (SNPs) in the IRF4 gene was conducted in 990 NHL cases and 828 controls from a multi-center US study. Measures of sun sensitivity and exposure were ascertained from computer-assisted personal interviews. We used logistic regression to compute odds ratios (OR) and 95% confidence intervals (CI) for NHL in relation to sun exposures, sun exposures in relation to IRF4 genotypes, and NHL in relation to sun exposures. We further assessed the effects of sun exposures in relation to IRF4 genotypes.

Results

As previously reported, we found significant associations between IRF4 rs12211228 and NHL and between hair and eye color and NHL. The IRF4 rs12203592 polymorphism (CT/TT genotype) was statistically significantly associated with eye color and particularly with hair color (OR_{Light Blonde} = 0.24, 95% CI = 0.11–0.50, overall Chi square p = 0.0002). Analysis of joint effects between eye and hair color with the IRF4 rs12203592 SNP did not reveal statistically significant p-interactions although NHL risk did decline with lighter hair color and presence of the variant IRF4 rs12203592 allele, compared to those without a variant allele and with black/brown hair color.

Conclusions

Our data do not statistically support a joint effect between IRF4 and sun sensitivity in mediating risk for NHL. Further evaluation of joint effects in other and larger populations is warranted.

Electronic supplementary material

The online version of this article (doi:10.1007/s10552-009-9348-5) contains supplementary material, which is available to authorized users.

Common gene variants in the tumor necrosis factor (TNF) and TNF receptor superfamilies and NF-kB transcription factors and non-Hodgkin lymphoma risk

BACKGROUND

A promoter polymorphism in the pro-inflammatory cytokine tumor necrosis factor (TNF) (TNF G-308A) is associated with increased non-Hodgkin lymphoma (NHL) risk. The protein product, TNF-alpha, activates the nuclear factor kappa beta (NF-kappaB) transcription factor, and is critical for inflammatory and apoptotic responses in cancer progression. We hypothesized that the TNF and NF-kappaB pathways are important for NHL and that gene variations across the pathways may alter NHL risk.

METHODOLOGY/PRINCIPAL FINDINGS

We genotyped 500 tag single nucleotide polymorphisms (SNPs) from 48 candidate gene regions (defined as 20 kb 5', 10 kb 3') in the TNF and TNF receptor superfamilies and the NF-kappaB and related transcription factors, in 1946 NHL cases and 1808 controls pooled from three independent population-based case-control studies. We obtained a gene region-level summary of association by computing the minimum p-value ("minP test"). We used logistic regression to compute odds ratios and 95% confidence intervals for NHL and four major NHL subtypes in relation to SNP genotypes and haplotypes. For NHL, the tail strength statistic supported an overall relationship between the TNF/NF-kappaB pathway and NHL (p = 0.02). We confirmed the association between TNF/LTA on chromosome 6p21.3 with NHL and found the LTA rs2844484 SNP most significantly and specifically associated with the major subtype, diffuse large B-cell lymphoma (DLBCL) (p-trend = 0.001). We also implicated for the first time, variants in NFKBIL1 on chromosome 6p21.3, associated with NHL. Other gene regions identified as statistically significantly associated with NHL included FAS, IRF4, TNFSF13B, TANK, TNFSF7 and TNFRSF13C. Accordingly, the single most significant SNPs associated with NHL were FAS rs4934436 (p-trend = 0.0024), IRF4 rs12211228 (p-trend = 0.0026), TNFSF13B rs2582869 (p-trend = 0.0055), TANK rs1921310 (p-trend = 0.0025), TNFSF7 rs16994592 (p-trend = 0.0024), and TNFRSF13C rs6002551 (p-trend = 0.0074). All associations were consistent in each study with no apparent specificity for NHL subtype.

CONCLUSIONS/SIGNIFICANCE

Our results provide consistent evidence that variation in the TNF superfamily of genes and specifically within chromosome 6p21.3 impacts lymphomagenesis. Further characterization of these susceptibility loci and identification of functional variants are warranted.

New tools to study the role of B cells in cytomegalovirus infections

B cells were previously shown to mediate partial protection against CMV infection, as in the absence of B cells, latently infected mice were more susceptible to virus reactivation. It remains unclear if this effect stems from the loss of B cells as antibody producers or as antigen presenting cells. To address this fundamental question, we propose to make use of new mouse models that allow conditional ablation of B cells or that allow for the generation of mice with B cells that are not able to produce antibodies.