Toll-like receptors and B-cell receptors synergize to induce immunoglobulin class-switch DNA recombination: relevance to microbial antibody responses

Relationships between Mucosal Antibodies, Non-Typeable Haemophilus influenzae (NTHi) Infection and Airway Inflammation in COPD

Non-typeable Haemophilus influenzae (NTHi) is a key pathogen in COPD, being associated with airway inflammation and risk of exacerbation. Why some patients are susceptible to colonisation is not understood. We hypothesised that this susceptibility may be due to a deficiency in mucosal humoral immunity. The aim of our study (NCT01701869) was to quantify the amount and specificity of antibodies against NTHi in the lungs and the associated risk of infection and inflammation in health and COPD. Phlebotomy, sputum induction and bronchoscopy were performed on 24 mild-to-moderate COPD patients and 8 age and smoking-matched controls. BAL (Bronchoalveolar lavage) total IgG1, IgG2, IgG3, IgM and IgA concentrations were significantly increased in COPD patients compared to controls. NTHi was detected in the lungs of 7 of the COPD patients (NTHi+ve-29%) and these patients had a higher median number of previous exacerbations than NTHi-ve patients as well as evidence of increased systemic inflammation. When comparing NTHi+ve versus NTHi-ve patients we observed a decrease in the amount of both total IgG1 (p = 0.0068) and NTHi-specific IgG1 (p = 0.0433) in the BAL of NTHi+ve patients, but no differences in total IgA or IgM. We observed no evidence of decreased IgG1 in the serum of NTHi+ve patients, suggesting this phenomenon is restricted to the airway. Furthermore, the NTHi+ve patients had significantly greater levels of IL-1β (p = 0.0003), in BAL than NTHi-ve COPD patients.This study indicates that the presence of NTHi is associated with reduced levels and function of IgG1 in the airway of NTHi-colonised COPD patients. This decrease in total and NTHI-specific IgG1 was associated with greater systemic and airway inflammation and a history of more frequent exacerbations and may explain the susceptibility of some COPD patients to the impacts of NTHi.

Analysis by Flow Cytometry of B-Cell Activation and Antibody Responses Induced by Toll-Like Receptors

Toll-like receptors (TLRs) are expressed in B lymphocytes and contribute to B-cell activation, antibody responses, and their maturation. TLR stimulation of mouse B cells induces class switch DNA recombination (CSR) to isotypes specified by cytokines, and also induces formation of IgM(+) as well as class-switched plasma cells. B-cell receptor (BCR) signaling, while on its own inducing limited B-cell proliferation and no CSR, can enhance CSR driven by TLRs. Particular synergistic or antagonistic interactions among TLR pathways, BCR, and cytokine signaling can have important consequences for B-cell activation, CSR, and plasma cell formation. This chapter outlines protocols for the induction and analysis of B-cell activation and antibody production by TLRs with or without other stimuli.

Follicular Helper T (Tfh) Cells in Autoimmune Diseases and Allograft Rejection

Production of high affinity antibodies for antigens is a critical component for the immune system to fight off infectious pathogens. However, it could be detrimental to our body when the antigens that B cells recognize are of self-origin. Follicular helper T, or Tfh, cells are required for the generation of germinal center reactions, where high affinity antibody-producing B cells and memory B cells predominantly develop. As such, Tfh cells are considered as targets to prevent B cells from producing high affinity antibodies against self-antigens, when high affinity autoantibodies are responsible for immunopathologies in autoimmune disorders. This review article provides an overview of current understanding of Tfh cells and discusses it in the context of animal models of autoimmune diseases and allograft rejections for generation of novel therapeutic interventions.

Regulation of B Cell Differentiation by Intracellular Membrane-Associated Proteins and microRNAs: Role in the Antibody Response

B cells are central to adaptive immunity and their functions in antibody responses are exquisitely regulated. As suggested by recent findings, B cell differentiation is mediated by intracellular membrane structures (including endosomes, lysosomes, and autophagosomes) and protein factors specifically associated with these membranes, including Rab7, Atg5, and Atg7. These factors participate in vesicle formation/trafficking, signal transduction and induction of gene expression to promote antigen presentation, class switch DNA recombination (CSR)/somatic hypermutation (SHM), and generation/maintenance of plasma cells and memory B cells. Their expression is induced in B cells activated to differentiate and further fine-tuned by immune-modulating microRNAs, which coordinates CSR/SHM, plasma cell differentiation, and memory B cell differentiation. These short non-coding RNAs would individually target multiple factors associated with the same intracellular membrane compartments and collaboratively target a single factor in addition to regulating AID and Blimp-1. These, together with regulation of microRNA biogenesis and activities by endosomes and autophagosomes, show that intracellular membranes and microRNAs, two broadly relevant cell constituents, play important roles in balancing gene expression to specify B cell differentiation processes for optimal antibody responses.

Rapid Proliferation and Differentiation of a Subset of Circulating IgM Memory B Cells to a CpG/Cytokine Stimulus In Vitro

Circulating human IgM expressing memory B cells have been incompletely characterized. Here, we compared the phenotype and in vitro functional response (capacity to proliferate and differentiate to antibody secreting cells) in response to CpG and a cytokine cocktail (IL-2, IL-6, and IL-10) of sorted naïve B cells, IgM memory B cells and isotype-switched circulating memory B cells. Compared to naïve B cells, IgM memory B cells had lower integrated mean fluorescence intensity (iMFI) of BAFF-R, CD38, CD73, and IL-21R, but higher iMFI of CD95, CD11c, TLR9, PD-1, and CD122. Compared to switched memory B cells, IgM memory B cells had higher iMFI of BAFF-R, PD-1, IL-21R, TLR9, and CD122, but lower iMFI of CD38, CD95, and CD73. Four days after receiving the CpG/cytokine cocktail, higher frequencies of IgM than switched memory B cells—and these in turn greater than naïve cells—proliferated and differentiated to antibody secreting cells. At this time point, a small percentage (median of 7.6%) of stimulated IgM memory B cells changed isotype to IgG. Thus, among the heterogeneous population of human circulating IgM memory B cells a subset is capable of a rapid functional response to a CpG/cytokine stimulus in vitro.

B cell TLR1/2, TLR4, TLR7 and TLR9 interact in induction of class switch DNA recombination: modulation by BCR and CD40, and relevance to T-independent antibody responses

Ig class switch DNA recombination (CSR) in B cells is crucial to the maturation of antibody responses. It requires IgH germline IH-CH transcription and expression of AID, both of which are induced by engagement of CD40 or dual engagement of a Toll-like receptor (TLR) and B cell receptor (BCR). Here, we have addressed cross-regulation between two different TLRs or between a TLR and CD40 in CSR induction by using a B cell stimulation system involving lipopolysaccharides (LPS). LPS-mediated long-term primary class-switched antibody responses and memory-like antibody responses in vivo and induced generation of class-switched B cells and plasma cells in vitro. Consistent with the requirement for dual TLR and BCR engagement in CSR induction, LPS, which engages TLR4 through its lipid A moiety, triggered cytosolic Ca2+ flux in B cells through its BCR-engaging polysaccharidic moiety. In the presence of BCR crosslinking, LPS synergized with a TLR1/2 ligand (Pam3CSK4) in CSR induction, but much less efficiently with a TLR7 (R-848) or TLR9 (CpG) ligand. In the absence of BCR crosslinking, R-848 and CpG, which per se induced marginal CSR, virtually abrogated CSR to IgG1, IgG2a, IgG2b, IgG3 and/or IgA, as induced by LPS or CD154 (CD40 ligand) plus IL-4, IFN-γ or TGF-β, and reduced secretion of class-switched Igs, without affecting B cell proliferation or IgM expression. The CSR inhibition by TLR9 was associated with the reduction in AID expression and/or IgH germline IH-S-CH transcription, and required co-stimulation of B cells by CpG with LPS or CD154. Unexpectedly, B cells also failed to undergo CSR or plasma cell differentiation when co-stimulated by LPS and CD154. Overall, by addressing the interaction of TLR1/2, TLR4, TLR7 and TLR9 in the induction of CSR and modulation of TLR-dependent CSR by BCR and CD40, our study suggests the complexity of how different stimuli cross-regulate an important B cell differentiation process and an important role of TLRs in inducing effective T-independent antibody responses to microbial pathogens, allergens and vaccines.

Syk is indispensable for CpG-induced activation and differentiation of human B cells

B cells are efficiently activated by CpG oligodeoxynucleotides (ODNs) to produce pro-inflammatory cytokines and antibody (Ab). Here, we describe a so far unidentified, spleen tyrosine kinase (Syk)-dependent pathway, which is indispensable for CpG-induced human B cell activation. We show that triggering of B cells by CpG results in Syk and src kinase phosphorylation, proliferation, as well as cytokine and Ab production independent of the BCR. Notably, all these functions are abrogated when Syk is inhibited. We demonstrate that CpG-induced Syk activation originates from the cell surface in a TLR9-dependent manner. While inhibition of Syk does not influence the uptake of CpG ODNs, activation of the kinase is a prerequisite for the delivery of CpG into TLR9-containing endolysosomes and for the CpG-induced up-regulation of TLR9 expression. Our results reveal an alternative, Syk-dependent pathway of CpG-induced B cell stimulation, which is initiated at the plasma membrane and seems to be an upstream requirement for endosomal TLR9-driven B cell proliferation and differentiation.

Surface Plasmon Resonance Analysis Shows an IgG-Isotype-Specific Defect in ABO Blood Group Antibody Formation in Patients with Common Variable Immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) is the most common clinically severe primary immunodeficiency and comprises a heterogeneous group of patients with recurrent severe bacterial infections due to the failure to produce IgG antibodies after exposure to infectious agents and immunization. Diagnostic recommendations for antibody failure include assessment of isoagglutinins. We have readdressed this four decades old but still accepted recommendation with up to date methodology.

METHODS

Anti-A/B IgM- and IgG-antibodies were measured by Diamed-ID Micro Typing, surface plasmon resonance (SPR) using the Biacore(®) device and flow cytometry.

RESULTS

When Diamed-ID Micro Typing was used, CVID patients (n = 34) showed IgG- and IgM-isoagglutinins that were comparable to healthy volunteers (n = 28), while all XLA patients (n = 8) had none. Anti-A/B IgM-antibodies were present in more than 2/3 of the CVID patients and showed binding kinetics comparable to anti-A/B IgM-antibodies from healthy individuals. A correlation could be found in CVID patients between levels of anti-A/B IgM-antibodies and levels of serum IgM and PnP-IgM-antibodies. In contrast in CVID patients as a group ABO antibodies were significantly decreased when assessed by SPR, which correlated with levels of switched memory, non-switched memory and naïve B cells, but all CVID patients had low/undetectable anti-A/B IgG-antibodies.

CONCLUSION

These results indicate that conventional isoagglutinin assessment and assessment of anti-A/B IgM antibodies are not suited for the diagnosis of impaired antibody production in CVID. Examination of anti-A/B IgG antibodies by SPR provides a useful method for the diagnosis of IgG antibody failure in all CVID patients studied, thus indicating an important additional rationale to start immunoglobulin replacement therapy early in these patients, before post-infectious sequelae develop.

Identification of a negative regulatory role for spi-C in the murine B cell lineage

Spi-C is an E26 transformation-specific family transcription factor that is highly related to PU.1 and Spi-B. Spi-C is expressed in developing B cells, but its function in B cell development and function is not well characterized. To determine whether Spi-C functions as a negative regulator of Spi-B (encoded by Spib), mice were generated that were germline knockout for Spib and heterozygous for Spic (Spib(-/-)Spic(+/-)). Interestingly, loss of one Spic allele substantially rescued B cell frequencies and absolute numbers in Spib(-/-) mouse spleens. Spib(-/-)Spic(+/-) B cells had restored proliferation compared with Spib(-/-) B cells in response to anti-IgM or LPS stimulation. Investigation of a potential mechanism for the Spib(-/-)Spic(+/-) phenotype revealed that steady-state levels of Nfkb1, encoding p50, were elevated in Spib(-/-)Spic(+/-) B cells compared with Spib(-/-) B cells. Spi-B was shown to directly activate the Nfkb1 gene, whereas Spi-C was shown to repress this gene. These results indicate a novel role for Spi-C as a negative regulator of B cell development and function.

Nfkb1 activation by the E26 transformation-specific transcription factors PU.1 and Spi-B promotes Toll-like receptor-mediated splenic B cell proliferation

Generation of antibodies against T-independent and T-dependent antigens requires Toll-like receptor (TLR) engagement on B cells for efficient responses. However, the regulation of TLR expression and responses in B cells is not well understood. PU.1 and Spi-B (encoded by Sfpi1 and Spib, respectively) are transcription factors of the E26 transformation-specific (ETS) family and are important for B cell development and function. It was found that B cells from mice knocked out for Spi-B and heterozygous for PU.1 (Sfpi1(+/-) Spib(-/-) [PUB] mice) proliferated poorly in response to TLR ligands compared to wild-type (WT) B cells. The NF-κB family member p50 (encoded by Nfkb1) is required for lipopolysaccharide (LPS) responsiveness in mice. PUB B cells expressed reduced Nfkb1 mRNA transcripts and p50 protein. The Nfkb1 promoter was regulated directly by PU.1 and Spi-B, as shown by reporter assays and chromatin immunoprecipitation analysis. Occupancy of the Nfkb1 promoter by PU.1 was reduced in PUB B cells compared to that in WT B cells. Finally, infection of PUB B cells with a retroviral vector encoding p50 substantially restored proliferation in response to LPS. We conclude that Nfkb1 transcriptional activation by PU.1 and Spi-B promotes TLR-mediated B cell proliferation.

Pathogen manipulation of B cells: the best defence is a good offence

B cells have long been regarded as simple antibody production units, but are now becoming known as key players in both adaptive and innate immune responses. However, several bacteria, viruses and parasites have evolved the ability to manipulate B cell functions to modulate immune responses. Pathogens can affect B cells indirectly, by attacking innate immune cells and altering the cytokine environment, and can also target B cells directly, impairing B cell-mediated immune responses. In this Review, we provide a summary of recent advances in elucidating direct B cell-pathogen interactions and highlight how targeting this specific cell population benefits different pathogens.

Activation-Induced Cytidine Deaminase and Switched Memory B Cells as Predictors of Effective In Vivo Responses to the Influenza Vaccine

Aging impairs humoral immune responses, leading to increased frequency and severity of infectious diseases and reduced protective effects of vaccination. We have identified B-cell biomarkers that are reduced by aging and that can be used as predictive markers of the response of an individual to vaccination. The identification of these biomarkers will have an impact on the development of effective vaccines to protect the elderly from infections and other debilitating diseases.

Epigenetic function of activation-induced cytidine deaminase and its link to lymphomagenesis

Activation-induced cytidine deaminase (AID) is essential for somatic hypermutation and class switch recombination of immunoglobulin (Ig) genes during B cell maturation and immune response. Expression of AID is tightly regulated due to its mutagenic and recombinogenic potential, which is known to target not only Ig genes, but also non-Ig genes, contributing to lymphomagenesis. In recent years, a new epigenetic function of AID and its link to DNA demethylation came to light in several developmental systems. In this review, we summarize existing evidence linking deamination of unmodified and modified cytidine by AID to base-excision repair and mismatch repair machinery resulting in passive or active removal of DNA methylation mark, with the focus on B cell biology. We also discuss potential contribution of AID-dependent DNA hypomethylation to lymphomagenesis.

Histone deacetylase inhibitors upregulate B cell microRNAs that silence AID and Blimp-1 expression for epigenetic modulation of antibody and autoantibody responses

Class-switch DNA recombination (CSR) and somatic hypermutation (SHM), which require activation-induced cytidine deaminase (AID), and plasma cell differentiation, which requires B lymphocyte-induced maturation protein-1 (Blimp-1), are critical for the generation of class-switched and hypermutated (mature) Ab and autoantibody responses. We show that histone deacetylase inhibitors valproic acid and butyrate dampened AICDA/Aicda (AID) and PRDM1/Prdm1 (Blimp-1) mRNAs by upregulating miR-155, miR-181b, and miR-361 to silence AICDA/Aicda, and miR-23b, miR-30a, and miR-125b to silence PRDM1/Prdm1, in human and mouse B cells. This led to downregulation of AID, Blimp-1, and X-box binding protein 1, thereby inhibiting CSR, SHM, and plasma cell differentiation without altering B cell viability or proliferation. The selectivity of histone deacetylase inhibitor-mediated silencing of AICDA/Aicda and PRDM1/Prdm1 was emphasized by unchanged expression of HoxC4 and Irf4 (important inducers/modulators of AICDA/Aicda), Rev1 and Ung (central elements for CSR/SHM), and Bcl6, Bach2, or Pax5 (repressors of PRDM1/Prdm1 expression), as well as unchanged expression of miR-19a/b, miR-20a, and miR-25, which are not known to regulate AICDA/Aicda or PRDM1/Prdm1. Through these B cell-intrinsic epigenetic mechanisms, valproic acid blunted class-switched and hypermutated T-dependent and T-independent Ab responses in C57BL/6 mice. In addition, it decreased class-switched and hypermutated autoantibodies, ameliorated disease, and extended survival in lupus MRL/Fas(lpr/lpr) mice. Our findings outline epigenetic mechanisms that modulate expression of an enzyme (AID) and transcription factors (Blimp-1 and X-box binding protein 1) that are critical to the B cell differentiation processes that underpin Ab and autoantibody responses. They also provide therapeutic proof-of-principle in autoantibody-mediated autoimmunity.

IL-10 regulates Aicda expression through miR-155

Aicda is a critical component of antibody class-switching in B cells. In this work, we study the impact of TLR4 activation and IL-10 stimulation on Aicda expression in B cells. Through the global analysis of miRNAs in response to TLR4 activation, in combination with IL-10 stimulation, we identified that IL-10 can suppress TLR4-induced miR-155 expression, an effect that resulted in enhanced Aicda expression. Furthermore, when preventing miR-155 control of Aicda expression, by genetic mutation of its target site in the Aicda mRNA, IL-10 could further potentiate Aicda expression. Given that miR-155 expression is lost, and expression levels of both Aicda and IL-10 are high in diseases, such as Burkitt's lymphoma, our results suggest a stringent and sophisticated control of Aicda by a novel IL-10/miR-155 axis, where the imbalance of IL-10 and/or miR-155 may contribute to disease pathogenesis.

IgG subclasses and allotypes: from structure to effector functions

Of the five immunoglobulin isotypes, immunoglobulin G (IgG) is most abundant in human serum. The four subclasses, IgG1, IgG2, IgG3, and IgG4, which are highly conserved, differ in their constant region, particularly in their hinges and upper CH2 domains. These regions are involved in binding to both IgG-Fc receptors (FcγR) and C1q. As a result, the different subclasses have different effector functions, both in terms of triggering FcγR-expressing cells, resulting in phagocytosis or antibody-dependent cell-mediated cytotoxicity, and activating complement. The Fc-regions also contain a binding epitope for the neonatal Fc receptor (FcRn), responsible for the extended half-life, placental transport, and bidirectional transport of IgG to mucosal surfaces. However, FcRn is also expressed in myeloid cells, where it participates in both phagocytosis and antigen presentation together with classical FcγR and complement. How these properties, IgG-polymorphisms and post-translational modification of the antibodies in the form of glycosylation, affect IgG-function will be the focus of the current review.

Could DNA-reactive B lymphocytes be activated through HIV-1 DNA-stimulation involving BCR/TLR-9 pathway to yield antibodies targeting viral DNA?

This paper discusses potential avenues to abate the last bulwark to the HIV-1 eradication i.e. viral reservoirs in the body, consisting mainly of viral DNA hidden, in latent form, into long-lived memory CD4+ T-cells, resulting unaffected by either drugs or immune system. Activation of the innate immune system is necessary for the induction of adaptive immune responses against invading pathogens. In part, this is achieved by recognition of molecules associated with infection by a plethora of pattern recognition receptors comprising Toll-like receptors (TLRs) which are express on numerous cells of immune system such as, dendritic cells and B cells, and are activated by some TLR ligands. TLR-9, localized in endosomal compartment, specifically recognizes unmethylated oligonucleotide sequences containing CpG motifs which are particularly abundant in microbial genome, including HIV-1 DNA. Naïve B cells are activated following antigen binding to the B cell receptor (BCR). The complex antigen/BCR, internalises and synergises with TLR leading to hyper activation of B cells and antibodies production. Cross-link of the BCR with TLR9, followed by upregulation of TLR-9, in response to self DNA-containing antigens, on DNA-specific B lymphocytes lead to the development of DNA-specific autoantibodies. This occur in systemic autoimmune disorders, such as, systemic lupus erythematosus (SLE). Although such DNA-specific B lymphocytes, are usually present in B cell repertoire at low frequency, they normally do not produce autoantibodies, they can be activated by antigen BCR ligation, with plasmacytoid dendritic cells (pDCs) providing helper signals. The hypothesis here derives by insight that stimulation of BCR, by exogenously added HIV-1 DNA, on potentially reactive HIV-1 DNA-specific B cells, from HIV-1 and/or HIV-1/SLE patients, co-cultured with autologous viral DNA-stimulated pDCs, could lead to desirable in vitro production of antibodies direct against HIV-1 DNA by involving BCR/TLR9 pathway. These antibodies, suitably delivered into infected or uninfected CD4(+) T-cells, by a carrier, such as, peptide transduction domain of Tat, could selectively recognize viral nucleic acid, rich in CpG motifs, respect to host DNA, both in productively than latently infected T cells. Because HIV-1 DNA into latently infected cells is heavily methylated and deacetylated, co-treatment with a small molecule inhibitor of DNA methylation, such as 5-aza-2'-deoxycytidine (aza-Cdr), and histone deacetylase inhibitors (HDACi), they would favor higher accessibility by antibodies to viral DNA, which is harbored into human chromosomes. The in vitro production of anti-HIV-1 DNA antibodies and their in vivo reintroduction, could find future application as interesting strategy to pave the way to an eventual cure to decrease and/or eliminate viral reservoirs from the body, and providing possible therapeutic applications not only for HIV-1/AIDS, but also for other infectious diseases.

Control of Toll-like receptor-mediated T cell-independent type 1 antibody responses by the inducible nuclear protein IκB-ζ

Antibody responses have been classified as being either T cell-dependent or T cell-independent (TI). TI antibody responses are further classified as being either type 1 (TI-1) or type 2 (TI-2), depending on their requirement for B cell-mediated antigen receptor signaling. Although the mechanistic basis of antibody responses has been studied extensively, it remains unclear whether different antibody responses share similarities in their transcriptional regulation. Here, we show that mice deficient in IκB-ζ, specifically in their B cells, have impaired TI-1 antibody responses but normal T cell-dependent and TI-2 antibody responses. The absence of IκB-ζ in B cells also impaired proliferation triggered by Toll-like receptor (TLR) activation, plasma cell differentiation, and class switch recombination (CSR). Mechanistically, IκB-ζ-deficient B cells could not induce TLR-mediated induction of activation-induced cytidine deaminase (AID), a class-switch DNA recombinase. Retroviral transduction of AID in IκB-ζ-deficient B cells restored CSR activity. Furthermore, acetylation of histone H3 in the vicinity of the transcription start site of the gene that encodes AID was reduced in IκB-ζ-deficient B cells relative to IκB-ζ-expressing B cells. These results indicate that IκB-ζ regulates TLR-mediated CSR by inducing AID. Moreover, IκB-ζ defines differences in the transcriptional regulation of different antibody responses.

Coinfection with Streptococcus pneumoniae modulates the B cell response to influenza virus

Pathogen-specific antibodies (Abs) protect against respiratory infection with influenza A virus (IAV) and Streptococcus pneumoniae and are the basis of effective vaccines. Sequential or overlapping coinfections with both pathogens are common, yet the impact of coinfection on the generation and maintenance of Ab responses is largely unknown. We report here that the B cell response to IAV is altered in mice coinfected with IAV and S. pneumoniae and that this response differs, depending on the order of pathogen exposure. In mice exposed to S. pneumoniae prior to IAV, the initial virus-specific germinal center (GC) B cell response is significantly enhanced in the lung-draining mediastinal lymph node and spleen, and there is an increase in CD4(+) T follicular helper (TFH) cell numbers. In contrast, secondary S. pneumoniae infection exaggerates early antiviral antibody-secreting cell formation, and at later times, levels of GCs, TFH cells, and antiviral serum IgG are elevated. Mice exposed to S. pneumoniae prior to IAV do not maintain the initially robust GC response in secondary lymphoid organs and exhibit reduced antiviral serum IgG with diminished virus neutralization activity a month after infection. Our data suggest that the history of pathogen exposures can critically affect the generation of protective antiviral Abs and may partially explain the differential susceptibility to and disease outcomes from IAV infection in humans. Importance: Respiratory tract coinfections, specifically those involving influenza A viruses and Streptococcus pneumoniae, remain a top global health burden. We sought to determine how S. pneumoniae coinfection modulates the B cell immune response to influenza virus since antibodies are key mediators of protection.

Gene expression profiling of the response to interferon beta in Epstein-Barr-transformed and primary B cells of patients with multiple sclerosis

The effects of interferon-beta (IFN-β), one of the key immunotherapies used in multiple sclerosis (MS), on peripheral blood leukocytes and T cells have been extensively studied. B cells are a less abundant leukocyte type, and accordingly less is known about the B cell-specific response to IFN-β. To identify gene expression changes and pathways induced by IFN-β in B cells, we studied the in vitro response of human Epstein Barr-transformed B cells (lymphoblast cell lines-LCLs), and validated our results in primary B cells. LCLs were derived from an MS patient repository. Whole genome expression analysis identified 115 genes that were more than two-fold differentially up-regulated following IFN-β exposure, with over 50 previously unrecognized as IFN-β response genes. Pathways analysis demonstrated that IFN-β affected LCLs in a similar manner to other cell types by activating known IFN-β canonical pathways. Additionally, IFN-β increased the expression of innate immune response genes, while down-regulating many B cell receptor pathway genes and genes involved in adaptive immune responses. Novel response genes identified herein, NEXN, DDX60L, IGFBP4, and HAPLN3, B cell receptor pathway genes, CD79B and SYK, and lymphocyte activation genes, LAG3 and IL27RA, were validated as IFN-β response genes in primary B cells. In this study new IFN-β response genes were identified in B cells, with possible implications to B cell-specific functions. The study's results emphasize the applicability of LCLs for studies of human B cell drug response. The usage of LCLs from patient-based repositories may facilitate future studies of drug response in MS and other immune-mediated disorders with a B cell component.

B lymphocytes undergo TLR2-dependent apoptosis upon Shigella infection

Shigella flexneri interacts with B cells and induces apoptosis via IpaD binding to TLR2.

Antibody-mediated immunity to Shigella, the causative agent of bacillary dysentery, requires several episodes of infection to get primed and is short-lasting, suggesting that the B cell response is functionally impaired. We show that upon ex vivo infection of human colonic tissue, invasive S. flexneri interacts with and occasionally invades B lymphocytes. The induction of a type three secretion apparatus (T3SA)–dependent B cell death is observed in the human CL-01 B cell line in vitro, as well as in mouse B lymphocytes in vivo. In addition to cell death occurring in Shigella-invaded CL-01 B lymphocytes, we provide evidence that the T3SA needle tip protein IpaD can induce cell death in noninvaded cells. IpaD binds to and induces B cell apoptosis via TLR2, a signaling receptor thus far considered to result in activation of B lymphocytes. The presence of bacterial co-signals is required to sensitize B cells to apoptosis and to up-regulate tlr2, thus enhancing IpaD binding. Apoptotic B lymphocytes in contact with Shigella-IpaD are detected in rectal biopsies of infected individuals. This study therefore adds direct B lymphocyte targeting to the diversity of mechanisms used by Shigella to dampen the host immune response.

Failure to detect functional neutrophil B helper cells in the human spleen

A novel role for human neutrophilic granulocytes was recently described, showing that these cells, upon entering the spleen, can be reprogrammed into a distinct B cell-helper neutrophil phenotype that is capable of eliciting B cell responses such as immunoglobulin secretion, class switch recombination and somatic hypermutation. Using similar protocols, we detected a homogeneous population of CD15^highCD16^high neutrophils in fresh human spleen samples, which did not differ in phenotype and function from blood neutrophils. No phenotypic characteristics of costimulatory nature were detected on splenic or circulating neutrophils, nor could we reproduce the immunoglobulin production of splenic B cells in the presence of splenic neutrophils, although B cell function and neutrophil activity were normal. Independent confirmation of a role for N_BH cells is required.

Scaffold functions of 14-3-3 adaptors in B cell immunoglobulin class switch DNA recombination

Class switch DNA recombination (CSR) of the immunoglobulin heavy chain (IgH) locus crucially diversifies antibody biological effector functions. CSR involves the induction of activation-induced cytidine deaminase (AID) expression and AID targeting to switch (S) regions by 14-3-3 adaptors. 14-3-3 adaptors specifically bind to 5'-AGCT-3' repeats, which make up for the core of all IgH locus S regions. They selectively target the upstream and downstream S regions that are set to undergo S-S DNA recombination. We hypothesized that 14-3-3 adaptors function as scaffolds to stabilize CSR enzymatic elements on S regions. Here we demonstrate that all seven 14-3-3β, 14-3-3ε, 14-3-3γ, 14-3-3η, 14-3-3σ, 14-3-3τ and 14-3-3ζ adaptors directly interacted with AID, PKA-Cα (catalytic subunit) and PKA-RIα (regulatory inhibitory subunit) and uracil DNA glycosylase (Ung). 14-3-3 adaptors, however, did not interact with AID C-terminal truncation mutant AIDΔ(180-198) or AIDF193A and AIDL196A point-mutants (which have been shown not to bind to S region DNA and fail to mediate CSR). 14-3-3 adaptors colocalized with AID and replication protein A (RPA) in B cells undergoing CSR. 14-3-3 and AID binding to S region DNA was disrupted by viral protein R (Vpr), an accessory protein of human immunodeficiency virus type-1 (HIV-1), which inhibited CSR without altering AID expression or germline IH-CH transcription. Accordingly, we demonstrated that 14-3-3 directly interact with Vpr, which in turn, also interact with AID, PKA-Cα and Ung. Altogether, our findings suggest that 14-3-3 adaptors play important scaffold functions and nucleate the assembly of multiple CSR factors on S regions. They also show that such assembly can be disrupted by a viral protein, thereby allowing us to hypothesize that small molecule compounds that specifically block 14-3-3 interactions with AID, PKA and/or Ung can be used to inhibit unwanted CSR.

Differential regulation of hepatic organic cation transporter 1, organic anion-transporting polypeptide 1a4, bile-salt export pump, and multidrug resistance-associated protein 2 transporter expression in lymphocyte-deficient mice associates with interleukin-6 production

Cholestasis results from interrupted bile flow and is associated with immune-mediated liver diseases. It is unclear how inflammation contributes to cholestasis. The aim of this study was to determine whether T and B cells contribute to hepatic transporter expression under basal and inflammatory conditions. C57BL/6J wild-type mice or strains lacking T, B, or both T and B cells were exposed to lipopolysaccharide (LPS) or saline, and livers were collected 16 hours later. Branched DNA signal amplification was used to assess mRNA levels of organic anion-transporting polypeptides (Oatp) 1a1, 1a4, and 1b2; organic cation transporter (Oct) 1; canalicular bile-salt export pump (Bsep); multidrug resistance-associated proteins (Mrp) 2 and 3; and sodium-taurocholate cotransporting polypeptide (Ntcp). Real-time polymerase chain reaction analysis was used to correlate changes of transporter expression with interleukin-1b (IL-1b), IL-6, IL-17A, IL-17F, tumor necrosis factor-α (TNF-α), and interferon-γ expression in the liver. LPS treatment inhibited Bsep and Oct1 mRNA expression, and this was abrogated with a loss of T cells, but not B cells. In addition, the absence of T cells increased Mrp2 mRNA expression, whereas B cell deficiency attenuated Oatp1a4 mRNA in LPS-treated mice. Oatp1a1, Oatp1b2, Ntcp, and Mrp3 were largely unaffected by T or B cell deficiency. Lymphocyte deficiency altered basal and inflammatory IL-6, but not TNF-α or IL-1b, mRNA expression. Taken together, these data implicate lymphocytes as regulators of basal and inflammatory hepatic transporter expression and suggest that IL-6 signaling may play a critical role.

Initial immunopathogenesis of multiple sclerosis: innate immune response

Multiple sclerosis (MS) is an inflammatory, demyelinating, and neurodegenerative disease of the central nervous system. The hallmark to MS is the demyelinated plaque, which consists of a well-demarcated hypocellular area characterized by the loss of myelin, the formation of astrocytic scars, and the mononuclear cell infiltrates concentrated in perivascular spaces composed of T cells, B lymphocytes, plasma cells, and macrophages. Activation of resident cells initiates an inflammatory cascade, leading to tissue destruction, demyelination, and neurological deficit. The immunological phenomena that lead to the activation of autoreactive T cells to myelin sheath components are the result of multiple and complex interactions between environment and genetic background conferring individual susceptibility. Within the CNS, an increase of TLR expression during MS is observed, even in the absence of any apparent microbial involvement. In the present review, we focus on the role of the innate immune system, the first line of defense of the organism, as promoter and mediator of cross reactions that generate molecular mimicry triggering the inflammatory response through an adaptive cytotoxic response in MS.

TLR3- and MyD88-dependent signaling differentially influences the development of West Nile virus-specific B cell responses in mice following immunization with RepliVAX WN, a single-cycle flavivirus vaccine candidate

Recognition of conserved pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) results in the activation of innate signaling pathways that drive the innate immune response and ultimately shape the adaptive immune response. RepliVAX WN, a single-cycle flavivirus (SCFV) vaccine candidate derived from West Nile virus (WNV), is intrinsically adjuvanted with multiple PAMPs and induces a vigorous anti-WNV humoral response. However, the innate mechanisms that link pattern recognition and development of vigorous antigen-specific B cell responses are not completely understood. Moreover, the roles of individual PRR signaling pathways in shaping the B cell response to this live attenuated SCFV vaccine have not been established. We examined and compared the role of TLR3- and MyD88-dependent signaling in the development of anti-WNV-specific antibody-secreting cell responses and memory B cell responses induced by RepliVAX WN. We found that MyD88 deficiency significantly diminished B cell responses by impairing B cell activation, development of germinal centers (GC), and the generation of long-lived plasma cells (LLPCs) and memory B cells (MBCs). In contrast, TLR3 deficiency had more effect on maintenance of GCs and development of LLPCs, whereas differentiation of MBCs was unaffected. Our data suggest that both TLR3- and MyD88-dependent signaling are involved in the intrinsic adjuvanting of RepliVAX WN and differentially contribute to the development of vigorous WNV-specific antibody and B cell memory responses following immunization with this novel SCFV vaccine.

Reinvestigating the role of IgM in rabies virus postexposure vaccination

B cells secreting IgG antibodies, but not IgM, are thought to be solely responsible for vaccine-induced protection against rabies virus (RABV) infections in postexposure settings. In this report, we reinvestigated the potential for IgM to mediate protection in a mouse model of RABV vaccination. Immunocompetent mice immunized with an experimental live replication-deficient RABV-based vaccine produced virus neutralizing antibodies (VNAs) within 3 days of vaccination. However, mice unable to produce soluble IgM (sIgM(-/-)) did not produce VNAs until 7 days postimmunization. Furthermore, sIgM(-/-) mice were not protected against RABV infection when challenged 3 days postimmunization, while all wild-type mice survived challenge. Consistent with the lack of protection against pathogenic RABV challenge, approximately 50- to 100-fold higher viral loads of challenge virus were detected in the muscle, spinal cord, and brain of immunized sIgM(-/-) mice compared to control mice. In addition, IgG antibody titers in vaccinated wild-type and sIgM(-/-) mice were similar at all time points postimmunization, suggesting that protection against RABV challenge is due to the direct effects of IgM and not the influence of IgM on the development of effective IgG antibody titers. In all, early vaccine-induced IgM can limit dissemination of pathogenic RABV to the central nervous system and mediate protection against pathogenic RABV challenge. Considering the importance for the rapid induction of VNAs to protect against RABV infections in postexposure prophylaxis settings, these findings may help guide the development of a single-dose human rabies vaccine.

AID in aging and autoimmune diseases

The aim of this study was to evaluate the quality of B cell responses in patients with Inflammatory Bowel Disease (IBD) and healthy individuals of different ages, vaccinated with the pandemic (p)2009 influenza vaccine. The in vivo response was measured by the hemagglutination inhibition (HAI) assay, which represents the most established correlate with vaccine protectiveness. The in vitro response was measured by activation-induced cytidine deaminase (AID) in cultures of vaccine-stimulated PBMC. Both responses are somewhat impaired in IBD patients undergoing anti-TNF-α treatment but these are much more decreased in IBD patients undergoing treatment with anti-TNF-α and immunosuppressive (IS) drugs. These latter patients had in vivo and in vitro B cell responses similar to those of elderly individuals. Moreover, as we have previously demonstrated in healthy subjects, the in vitro response to the polyclonal stimulus CpG may be used as a biomarker for subsequent vaccine response and AID activation is correlated with the serum response in IBD patients, as it is in healthy individuals. These results altogether indicate that IBD patients on anti-TNF-α and IS have significantly impaired in vivo and in vitro B cell responses, as compared to those on monotherapy. This is the first report to demonstrate that B cell defects, as measured by the autonomous AID reporter, in IBD patients contribute to reduced humoral responses to the influenza vaccine, as we have previously shown for elderly individuals.

Division of labor during primary humoral immunity

B lymphocytes are often considered a homogenous population. However, B cells in both mouse and humans are comprised of distinct subpopulations that differ in development, phenotype, function, and microenvironmental niches. Much of our understanding about how these different B-cells populations mount antibody responses has been derived from experimental findings in mouse models and based on the use of model antigens. These reductionist studies performed over decades have been invaluable in defining the parameters of the B-cell antibody response to different types of antigens. However, these antigens also are now known to differ in a significant manner from bona fide physiological pathogens, and precisely how these different B-cell subsets divide labor in the primary humoral immune defense of pathogens is less well understood. While there are no absolutes in this area, there are recurring themes that divide the roles of B-cell subsets to different arms of the antibody response. This review provides an overview of rules that govern the B-cell labor roles, exceptions that break these rules, and models that have been used to define them.

B cell infection and activation by rabies virus-based vaccines

Replication-deficient rabies viruses (RABV) are promising rabies postexposure vaccines due to their prompt and potent stimulation of protective virus neutralizing antibody titers, which are produced in mice by both T-dependent and T-independent mechanisms. To promote such early and robust B cell stimulation, we hypothesized that live RABV-based vaccines directly infect B cells, thereby activating a large pool of antigen-presenting cells (APCs) capable of providing early priming and costimulation to CD4(+) T cells. In this report, we show that live RABV-based vaccine vectors efficiently infect naive primary murine and human B cells ex vivo. Infection of B cells resulted in the significant upregulation of early markers of B cell activation and antigen presentation, including CD69, major histocompatibility complex class II (MHC-II), and CD40 in murine B cells or HLA-DR and CD40 in human B cells compared to mock-infected cells or cells treated with an inactivated RABV-based vaccine. Furthermore, primary B cells infected with a live RABV expressing ovalbumin were able to prime and stimulate naive CD4(+) OT-II T cells to proliferate and to secrete interleukin-2 (IL-2), demonstrating a functional consequence of B cell infection and activation by live RABV-based vaccine vectors. We propose that this direct B cell stimulation by live RABV-based vaccines is a potential mechanism underlying their induction of early protective T cell-dependent B cell responses, and that designing live RABV-based vaccines to infect and activate B cells represents a promising strategy to develop a single-dose postexposure rabies vaccine where the generation of early protective antibody titers is critical.

Effects of age on H1N1-specific serum IgG1 and IgG3 levels evaluated during the 2011-2012 influenza vaccine season

BACKGROUND

We have previously reported an age-related impairment in the serum antibody response to pandemic (p)2009 H1N1, measured by hemagglutination inhibition assay and ELISA. The present study extends these observations and evaluates IgG subclass distribution in healthy individuals of different ages vaccinated during the 2011-2012 season.

RESULTS

The 2011-2012 vaccination season was characterized by a vaccine containing the pandemic (p)2009 H1N1 strain for the third consecutive year. All of our subjects were previously immunized, and therefore seroprotected at t0. Nevertheless, aging impaired the serum antibody response to H1N1, as antibody titers increased after vaccination in young and less in elderly individuals. The peak of the response was at day 7 (t7), in contrast with what is usually seen at day 21-28, suggesting a memory response characterized by the induction of an IgG subclass with a shorter half-life. We hypothesized that the IgG3 response, with its much shorter half-life, might be more represented. Antibodies were predominantly of the IgG1 subclass in both age groups, although a robust IgG3 response was also induced and accounted for a significant proportion of the overall response. IgG2 and IgG4 antibodies were at indiscernible levels. We showed a much higher percentage of IgG3 (40-50%) than previously in the literature (less than 10%). To explain if this was associated with a particular cytokine profile, we measured H1N1-induced T cell cytokines in vitro and found that IgG3 levels were positively correlated with TNF-α and IL-6. Moreover, activation-induced cytidine deaminase (AID) mRNA expression, a predictive biomarker of optimal in vivo vaccine response, was found to significantly correlate with IgG3 and also with IgG1 similar to what we have shown previously for total IgG.

CONCLUSIONS

In the 2011-2012 season, the pandemic (p)2009 H1N1 strain was present in the vaccine for the third consecutive year and therefore each individual was seroprotected at t0. The peak of the response was at t7, suggesting a memory response characterized by a robust induction of IgG3, which was associated with TNF-α and IL-6 production. Both IgG1 and IgG3 responses were decreased by age. AID was confirmed to be a predictive biomarker of optimal vaccine responses.

Emphasis on the Role of PF4 in the Incidence, Pathophysiology and Treatment of Heparin Induced Thrombocytopenia

Heparin Induced Thrombocytopenia (HIT) is caused by antibodies that recognize platelet factor 4 (PF4) associated with polyanionic glycosaminoglycan drugs or displayed on vascular cell membranes. These antibodies are elicited by multimolecular complexes that can occur when heparin is administered in clinical settings associated with abundant PF4. Heparin binding alters native PF4 and elicits immune recognition and response. While the presence of heparin is integral to immunogenesis, the HIT antibody binding site is within PF4. Thus HIT antibodies develop and function to cause thrombocytopenia and/or thrombosis only in the presence of PF4. Future emphasis on understanding the biology, turnover and regulation of PF4 may lead to insights into the prevention and treatment of HIT.

Regulation of Aicda expression and AID activity

Activation-induced cytidine deaminase (AID) is expressed in a B cell differentiation stage-specific fashion and is essential for immunoglobulin (Ig) gene class switch DNA recombination (CSR) and somatic hypermutation (SHM). CSR and SHM play a central role in the maturation of antibody and autoantibody responses. AID displays a mutagenic activity by catalyzing targeted deamination of deoxycytidine (dC) residues in DNA resulting in dU:dG mismatches, which are processed into point-mutations in SHM or double-strand breaks (DSBs) in CSR. Although AID specifically targets the Ig gene loci (IgH, Igκ and Igλ), it can also home into a wide array of non-Ig genes in B-and non-B-cell backgrounds. Aberrant expression of AID is associated with multiple diseases such as allergy, inflammation, autoimmunity and cancer. In autoimmune systemic lupus erythematosus, dysregulated AID expression underpins increased CSR, SHM and autoantibody production. As a potent mutator, AID is under stringent transcriptional, post-transcriptional and post-translational regulation. AID is also regulated in its targeting and enzymatic function. In resting naïve or memory B cells, AID transcripts and protein are undetectable. These, however, are readily and significantly up-regulated in B cells induced to undergo CSR and/or SHM. Transcription factors, such as HoxC4 and NF-κB, which are up-regulated in a B cell lineage-and/or differentiation stage-specific manner, regulate the induction of AID. HoxC4 induces AID expression by directly binding to the AID gene promoter through an evolutionarily conserved 5'-ATTT-3' motif. HoxC4 is induced by the same stimuli that induce AID and CSR. It is further up-regulated by estrogen through three estrogen responsive elements in its promoter region. The targeting of AID to switch (S) regions is mediated by 14-3-3 adaptor proteins, which specifically bind to 5'-AGCT-3' repeats that are exist at high frequency in S region cores. Like HoxC4, 14-3-3 adaptors are induced by the same stimuli that induce AID. These include "primary" inducing stimuli, that is, those that play a major role in inducing AID, i.e., engagement of CD40 by CD154, engagement of Toll-like receptors (TLRs) by microbial-associated molecular patterns (MAMPs) and cross-linking of the BCR, as synergized by "secondary" inducing stimuli, that is, those that synergize for AID induction and specify CSR to different isotypes, i.e., switch-directing cytokines IL-4, TGF-β or IFN-γ. In this review, we focus on the multi-levels regulation of AID expression and activity. We also discuss the dysregulation or misexpression of AID in autoimmunity and tumorigenesis.

Aberrant TIRAP and MyD88 expression in B-cell chronic lymphocytic leukemia

TIRAP and Myd88 are adaptor proteins for Toll-like receptors-2 and -4 (TLR2/4) which are engaged in transducing the signal to downstream molecules. Several studies have shown the increased role of infection factors in pathogenesis of B cell chronic lymphocytic leukemia (B-CLL). This prompted us to test whether there is a correlation between MyD88-TIRAP dynamics before and after inflammatory stimuli. We determined the mRNA and protein expression of TIRAP and MyD88 in CD5(+)CD19(+) B-CLL cells and in a subpopulation of normal B CD19(+) lymphocytes. Additionally we determined the influence of lipopolysaccharide Escherichia coli - TLR4-ligand (LPS) and Staphylococcus aureus strain Cowan I - TLR2-ligand (SAC) on TIR-domain-containing adaptor protein, also called MyD88 adaptor-like (TIRAP) and myeloid differentiation primary response protein 88 (MyD88) expression. We have found that the mRNA and protein expression of TIRAP and MyD88 in B-CLL lymphocytes is lower compared with that in normal B lymphocytes. LPS and SAC stimulation in normal lymphocytes significantly altered neither TIRAP nor MyD88 mRNA expression, whereas TIRAP protein level substantially decreased after TLR agonist treatment. We did not observe any changes in MyD88 protein level after B lymphocyte stimulation. There was a significant increase in TIRAP mRNA expression after LPS and SAC stimulation of B-CLL cells. MyD88 mRNA expression levels in B-CLL lymphocytes slightly decreased upon treatment with either stimulator. Stimulation with TLR agonists did not cause changes in TIRAP and MyD88 expression at the protein level in B-CLL lymphocytes. The results of our study suggest that there may exist a, yet unknown, defect of TIRAP and MyD88 proteins in B-CLL lymphocytes.

Splenic proliferative lymphoid nodules distinct from germinal centers are sites of autoantigen stimulation in immune thrombocytopenia

To understand more specific abnormalities of humoral autoimmunity, we studied 31 spleens from immune thrombocytopenia (ITP) patients and 36 control spleens. Detailed analysis identified at least 2 different splenic structures accommodating proliferating B cells, classic germinal centers (GCs), and proliferative lymphoid nodules (PLNs). PLNs were characterized by proliferating Ki67+ B cells close to follicular dendritic cells (FDCs) and lacked polarization into dark and light zones. As opposed to cells in GCs, proliferating B cells in PLN lacked expression of Bcl6. In both PLNs and GCs of ITP spleens, the density of T cells was significantly reduced. Both T follicular helper cells (TFH) and regulatory T cells were reduced within PLNs of ITP spleens suggesting a defect of tolerance related to a loss of T-cell control. Within PLNs of ITP, but not controls, abundant platelet glycoprotein (GP) IIb/IIIa autoantigens was found in IgM containing immune complexes tightly bound to FDCs and closely approximated to proliferating B cells. GPIV was found less often, but not in the same PLNs as GPIIb/IIIa. Autoantigens were not found in the GCs of ITP or controls indicating that PLNs are the sites of autoantigen stimulation in ITP potentially related to a lack of control by T cells and/or the present autoantigen.

TLR4- and TRIF-dependent stimulation of B lymphocytes by peptide liposomes enables T cell-independent isotype switch in mice

Immunoglobulin class switching from IgM to IgG in response to peptides is generally T cell-dependent and vaccination in T cell-deficient individuals is inefficient. We show that a vaccine consisting of a dense array of peptides on liposomes induced peptide-specific IgG responses totally independent of T-cell help. Independency was confirmed in mice lacking T cells and in mice deficient for MHC class II, CD40L, and CD28. The IgG titers were high, long-lived, and comparable with titers obtained in wild-type animals, and the antibody response was associated with germinal center formation, expression of activation-induced cytidine deaminase, and affinity maturation. The T cell-independent (TI) IgG response was strictly dependent on ligation of TLR4 receptors on B cells, and concomitant TLR4 and cognate B-cell receptor stimulation was required on a single-cell level. Surprisingly, the IgG class switch was mediated by TIR-domain-containing adapter inducing interferon-β (TRIF), but not by MyD88. This study demonstrates that peptides can induce TI isotype switching when antigen and TLR ligand are assembled and appropriately presented directly to B lymphocytes. A TI vaccine could enable efficient prophylactic and therapeutic vaccination of patients with T-cell deficiencies and find application in diseases where induction of T-cell responses contraindicates vaccination, for example, in Alzheimer disease.

Protective vaccine-induced CD4(+) T cell-independent B cell responses against rabies infection

A major goal in rabies virus (RV) research is to develop a single-dose postexposure prophylaxis (PEP) that would simplify vaccination protocols, reduce costs associated with rabies prevention in humans, and save lives. Live replication-deficient RV-based vaccines are emerging as promising single-dose vaccines to replace currently licensed inactivated RV-based vaccines. Nonetheless, little is known about how effective B cells develop in response to live RV-based vaccination. Understanding this fundamental property of rabies immunology may help in developing a single-dose RV vaccine. Typically, vaccines induce B cells secreting high-affinity, class-switched antibodies during germinal center (GC) reactions; however, there is a lag time between vaccination and the generation of GC B cells. In this report, we show that RV-specific antibodies are detected in mice immunized with live but not inactivated RV-based vaccines before B cells displaying a GC B cell phenotype (B220(+)GL7(hi)CD95(hi)) are formed, indicating a potential role for T cell-independent and early extrafollicular T cell-dependent antibody responses in the protection against RV infection. Using two mouse models of CD4(+) T cell deficiency, we show that B cells secreting virus-neutralizing antibodies (VNAs) are induced via T cell-independent mechanisms within 4 days postimmunization with a replication-deficient RV-based vaccine. Importantly, mice that are completely devoid of T cells (B6.129P2-Tcrβ(tm1Mom) Tcrδ(tm1Mom)/J) show protection against pathogenic challenge shortly after immunization with a live replication-deficient RV-based vaccine. We show that vaccines that can exploit early pathways of B cell activation and development may hold the key for the development of a single-dose RV vaccine wherein the rapid induction of VNA is critical.

Effect of prophylactically applied CpG ODN on the development of myocarditis in mice infected with Coxsackievirus B3

Coxsackievirus B3 was one of the major pathogens causing viral myocarditis. Toll-like receptor 9 activation contributed to the innate immune response in the process of CVB3-induced myocarditis. In order to find out how CpG oligodeoxynucleotide, known as a TLR-9 agonist, would affect the CVB3-induced myocarditis, we chose a C-type CpG oligodeoxynucleotide (YW002) injected to the mice one day before CVB3 challenge. On day 4 post CVB3 infection, 3 mice in each group were randomly sacrificed and their hearts were isolated to detect CVB3 replication. On day 10, the CVB3 neutralizing antibody and inflammatory change of the hearts were detected. The results indicated that the CVB3-induced myocarditis was aggravated with the declining body weight of mice, decreasing neutralizing antibody, and uncontrolling virus replication by injecting 20 μg YW002 per mouse. When adjusted the amount at 10 μg YW002 per mouse, there were no signs of aggravation in myocarditis. Plus, the mortality of the infected mice was reduced, the neutralizing antibody level was raised and the replication of virus was restrained. These results suggested that a proper amount of CpG oligodeoxynucleotide application could help to inhibit CVB3 infection.

Avian resistance to Campylobacter jejuni colonization is associated with an intestinal immunogene expression signature identified by mRNA sequencing

Campylobacter jejuni is the most common cause of human bacterial gastroenteritis and is associated with several post-infectious manifestations, including onset of the autoimmune neuropathy Guillain-Barré syndrome, causing significant morbidity and mortality. Poorly-cooked chicken meat is the most frequent source of infection as C. jejuni colonizes the avian intestine in a commensal relationship. However, not all chickens are equally colonized and resistance seems to be genetically determined. We hypothesize that differences in immune response may contribute to variation in colonization levels between susceptible and resistant birds. Using high-throughput sequencing in an avian infection model, we investigate gene expression associated with resistance or susceptibility to colonization of the gastrointestinal tract with C. jejuni and find that gut related immune mechanisms are critical for regulating colonization. Amongst a single population of 300 4-week old chickens, there was clear segregation in levels of C. jejuni colonization 48 hours post-exposure. RNAseq analysis of caecal tissue from 14 C. jejuni-susceptible and 14 C. jejuni-resistant birds generated over 363 million short mRNA sequences which were investigated to identify 219 differentially expressed genes. Significantly higher expression of genes involved in the innate immune response, cytokine signaling, B cell and T cell activation and immunoglobulin production, as well as the renin-angiotensin system was observed in resistant birds, suggesting an early active immune response to C. jejuni. Lower expression of these genes in colonized birds suggests suppression or inhibition of a clearing immune response thus facilitating commensal colonization and generating vectors for zoonotic transmission. This study describes biological processes regulating C. jejuni colonization of the avian intestine and gives insight into the differential immune mechanisms incited in response to commensal bacteria in general within vertebrate populations. The results reported here illustrate how an exaggerated immune response may be elicited in a subset of the population, which alters host-microbe interactions and inhibits the commensal state, therefore having wider relevance with regard to inflammatory and autoimmune disease.

Immunoglobulin class-switch DNA recombination: induction, targeting and beyond

Class-switch DNA recombination (CSR) of the immunoglobulin heavy chain (IGH) locus is central to the maturation of the antibody response and crucially requires the cytidine deaminase AID. CSR involves changes in the chromatin state and the transcriptional activation of the IGH locus at the upstream and downstream switch (S) regions that are to undergo S-S DNA recombination. In addition, CSR involves the induction of AID expression and the targeting of CSR factors to S regions by 14-3-3 adaptors, and it is facilitated by the transcription machinery and by histone modifications. In this Review, we focus on recent advances regarding the induction and targeting of CSR and outline an integrated model of the assembly of macromolecular complexes that transduce crucial epigenetic information to enzymatic effectors of the CSR machinery.

B cell TLRs and induction of immunoglobulin class-switch DNA recombination

Toll-like receptors (TLRs) are a family of conserved pattern recognition receptors (PRRs). Engagement of B cell TLRs by microbe-associated molecular patterns (MAMPs) induces T-independent (TI) antibody responses and plays an important role in the early stages of T-dependent (TD) antibody responses before specific T cell help becomes available. The role of B cell TLRs in the antibody response is magnified by the synergy of B cell receptor (BCR) crosslinking and TLR engagement in inducing immunoglobulin (Ig) class switch DNA recombination (CSR), which crucially diversifies the antibody biological effector functions. Dual BCR/TLR engagement induces CSR to all Ig isotypes, as directed by cytokines, while TLR engagement alone induces marginal CSR. Integration of BCR and TLR signaling results in activation of the canonical and non-canonical NF-κB pathways, induction of activation-induced cytidine deaminase (AID) and germline transcription of IgH switch (S) regions. A critical role of B cell TLRs in CSR and the antibody response is emphasized by the emergence of several TLR ligands as integral components of vaccines that greatly boost humoral immunity in a B cell-intrinsic fashion.

BCR-signalling synergizes with TLR-signalling for induction of AID and immunoglobulin class-switching through the non-canonical NF-κB pathway

By diversifying antibody biological effector functions, class switch DNA recombination has a central role in the maturation of the antibody response. Here we show that BCR-signalling synergizes with Toll-like receptor (TLR) signalling to induce class switch DNA recombination. BCR-signalling activates the non-canonical NF-κB pathway and enhances the TLR-dependent canonical NF-κB pathway, thereby inducing activation-induced cytidine deaminase (AID), which is critical for class switch DNA recombination. Escherichia coli lipopolysaccharide (LPS) triggers dual TLR4/BCR-signalling and induces hallmarks of BCR-signalling, including CD79a phosphorylation and Ca(2+) mobilization, and activates both the NF-κB pathways to induce AID and class switch DNA recombination in a PI(3)K p85α-dependent fashion. CD40-signalling activates the two NF-κB pathways to induce AID and class switch DNA recombination independent of BCR-signalling. Finally, dual BCR/TLR-engaging NP-lipopolysaccharide effectively elicits class-switched NP-specific IgG3 and IgG2b in mice. Thus, by integrating signals of the non-canonical and canonical NF-κB pathways, BCR and TLRs synergize to induce AID and T-cell-independent class switch DNA recombination.

Toll-like receptor signaling pathway in chronic lymphocytic leukemia: distinct gene expression profiles of potential pathogenic significance in specific subsets of patients

BACKGROUND

Signaling through the B-cell receptor appears to be a major contributor to the pathogenesis of chronic lymphocytic leukemia. Toll-like receptors bridge the innate and adaptive immune responses by acting as co-stimulatory signals for B cells. The available data on the expression of Toll-like receptors in chronic lymphocytic leukemia are limited and derive from small series of patients.

DESIGN AND METHODS

We profiled the expression of genes associated with Toll-like receptor signaling pathways in 192 cases of chronic lymphocytic leukemia and explored potential associations with molecular features of the clonotypic B-cell receptors.

RESULTS

Chronic lymphocytic leukemia cells express all Toll-like receptors expressed by normal activated B cells, with high expression of TLR7 and CD180, intermediate expression of TLR1, TLR6, TLR10 and low expression of TLR2 and TLR9. The vast majority of adaptors, effectors and members of the NFKB, JNK/p38, NF/IL6 and IRF pathways are intermediately-to-highly expressed, while inhibitors of Toll-like receptor activity are generally low-to-undetectable, indicating that the Toll-like receptor-signaling framework is competent in chronic lymphocytic leukemia. Significant differences were identified for selected genes between cases carrying mutated or unmutated IGHV genes or assigned to different subsets with stereotyped B-cell receptors. The differentially expressed molecules include receptors, NFκB/MAPK signaling molecules and final targets of the cascade.

CONCLUSIONS

The observed variations are suggestive of distinctive activation patterns of the Toll-like receptor signaling pathway in subgroups of cases of chronic lymphocytic leukemia defined by the molecular features of B-cell receptors. Additionally, they indicate that different or concomitant signals acting through receptors other than the B-cell receptor can affect the behavior of the malignant clone.