Deletion of microRNA-155 reduces autoantibody responses and alleviates lupus-like disease in the Fas(lpr) mouse.

MicroRNA-155 (miR-155) regulates antibody responses and subsequent B-cell effector functions to exogenous antigens. However, the role of miR-155 in systemic autoimmunity is not known. Using the death receptor deficient (Fas(lpr)) lupus-prone mouse, we show here that ablation of miR-155 reduced autoantibody responses accompanied by a decrease in serum IgG but not IgM anti-dsDNA antibodies and a reduction of kidney inflammation. MiR-155 deletion in Fas(lpr) B cells restored the reduced SH2 domain-containing inositol 5'-phosphatase 1 to normal levels. In addition, coaggregation of the Fc γ receptor IIB with the B-cell receptor in miR-155(-/-)-Fas(lpr) B cells resulted in decreased ERK activation, proliferation, and production of switched antibodies compared with miR-155 sufficient Fas(lpr) B cells. Thus, by controlling the levels of SH2 domain-containing inositol 5'-phosphatase 1, miR-155 in part maintains an activation threshold that allows B cells to respond to antigens.

Adaptive immunity and adipose tissue biology.

Studies of immunity typically focus on understanding how hematopoietic cells interact within conventional secondary lymphoid tissues. However, immune reactions and their regulation occur in various environments within the body. Adipose tissue is one tissue that can influence and be influenced by adjacent and embedded lymphocytes. Despite the abundance and wide distribution of such tissue, and despite a growing obesity epidemic, studies of these interactions have been only marginally appreciated in the past. Here, we review advances in understanding of lymphoid structures within adipose tissue, the relationship between adipose tissue and adaptive immune function, and evidence for how this relationship contributes to obesity-associated diseases.

Contributions of antinucleoprotein IgG to heterosubtypic immunity against influenza virus.

Influenza A virus causes recurring seasonal epidemics and occasional influenza pandemics. Because of changes in envelope glycoprotein Ags, neutralizing Abs induced by inactivated vaccines provide limited cross-protection against new viral serotypes. However, prior influenza infection induces heterosubtypic immunity that accelerates viral clearance of a second strain, even if the external proteins are distinct. In mice, cross-protection can also be elicited by systemic immunization with the highly conserved internal nucleoprotein (NP). Both T lymphocytes and Ab contribute to such cross-protection. In this paper, we demonstrate that anti-NP IgG specifically promoted influenza virus clearance in mice by using a mechanism involving both FcRs and CD8(+) cells. Furthermore, anti-NP IgG rescued poor heterosubtypic immunity in B cell-deficient mice, correlating with enhanced NP-specific CD8 T cell responses. Thus, Ab against this conserved Ag has potent antiviral activity both in naive and in influenza-immune subjects. Such antiviral activity was not seen when mice were vaccinated with another internal influenza protein, nonstructural 1. The high conservation of NP Ag and the known longevity of Ab responses suggest that anti-NP IgG may provide a critically needed component of a universal influenza vaccine.

Regulation of antinucleoprotein IgG by systemic vaccination and its effect on influenza virus clearance.

Seasonal influenza epidemics recur due to antigenic drift of envelope glycoprotein antigens and immune evasion of circulating viruses. Additionally, antigenic shift can lead to influenza pandemics. Thus, a universal vaccine that protects against multiple influenza virus strains could alleviate the continuing impact of this virus on human health. In mice, accelerated clearance of a new viral strain (cross-protection) can be elicited by prior infection (heterosubtypic immunity) or by immunization with the highly conserved internal nucleoprotein (NP). Both heterosubtypic immunity and NP-immune protection require antibody production. Here, we show that systemic immunization with NP readily accelerated clearance of a 2009 pandemic H1N1 influenza virus isolate in an antibody-dependent manner. However, human immunization with trivalent inactivated influenza virus vaccine (TIV) only rarely and modestly boosted existing levels of anti-NP IgG. Similar results were observed in mice, although the reaction could be enhanced with adjuvants, by adjusting the stoichiometry among NP and other vaccine components, and by increasing the interval between TIV prime and boost. Importantly, mouse heterosubtypic immunity that had waned over several months could be enhanced by injecting purified anti-NP IgG or by boosting with NP protein, correlating with a long-lived increase in anti-NP antibody titers. Thus, current immunization strategies poorly induce NP-immune antibody that is nonetheless capable of contributing to long-lived cross-protection. The high conservation of NP antigen and the known longevity of antibody responses suggest that the antiviral activity of anti-NP IgG may provide a critically needed component of a universal influenza vaccine.

A novel role for non-neutralizing antibodies against nucleoprotein in facilitating resistance to influenza virus.

Current influenza vaccines elicit Abs to the hemagglutinin and neuraminidase envelope proteins. Due to antigenic drift, these vaccines must be reformulated annually to include the envelope proteins predicted to dominate in the following season. By contrast, vaccination with the conserved nucleoprotein (NP) elicits immunity against multiple serotypes (heterosubtypic immunity). NP vaccination is generally thought to convey protection primarily via CD8 effector mechanisms. However, significant titers of anti-NP Abs are also induced, yet the involvement of Abs in protection has largely been disregarded. To investigate how Ab responses might contribute to heterosubtypic immunity, we vaccinated C57BL/6 mice with soluble rNP. This approach induced high titers of NP-specific serum Ab, but only poorly detectable NP-specific T cell responses. Nevertheless, rNP immunization significantly reduced morbidity and viral titers after influenza challenge. Importantly, Ab-deficient mice were not protected by this vaccination strategy. Furthermore, rNP-immune serum could transfer protection to naive hosts in an Ab-dependent manner. Therefore, Ab to conserved, internal viral proteins, such as NP, provides an unexpected, yet important mechanism of protection against influenza. These results suggest that vaccines designed to elicit optimal heterosubtypic immunity to influenza should promote both Ab and T cell responses to conserved internal proteins.

CD28 and inducible costimulator (ICOS) signalling can sustain CD154 expression on activated T cells.

The biological outcome of receptor-mediated signalling often depends on the duration of engagement. Because CD40 signalling is controlled by the regulated expression of its ligand, CD154, the mechanisms that regulate CD154 expression probably determine the strength and duration of CD40 signalling. Here, we demonstrate that CD154 expression on the surface of mouse CD4 T cells can be separated into an early phase, occurring between 0 and 24 hr after T-cell activation, and a later extended phase, occurring after 24 hr. The early phase of CD154 expression did not require costimulation and was probably influenced by the strength of T-cell receptor (TCR) signalling alone. However, later CD154 expression was highly dependent on costimulation through either CD28 or inducible costimulator (ICOS). Although CD28 signalling interleukin (IL)-2 secretion, ICOS not, suggesting that costimulation enhance CD154 expression independently of IL-2 production. In fact, anti-CD28 treatment could still induce late-phase CD154 on anti-CD3-stimulated CD4 T cells expressing a mutated form of CD28 that not lead to the induction of IL-2. However, this CD154 induction was somewhat weaker than that of wild-type CD28-expressing cells, suggesting that direct signalling and IL-2-mediated signalling co-operatively responsible for the levels of CD154 induced by CD28. Finally, we show that the second phase of CD154 expression negatively regulated B-cell terminal differentiation and antibody secretion. These results demonstrate that TCR signalling and costimulation each regulate different phases of CD154 expression and control the biological outcome of CD40 signalling on B cells.

Antibody class switching: uncoupling S region accessibility from transcription.

Immunogloblin class switch recombination (CSR) is a regulated process that changes antibody effector functions. Recently, Nambu et al. showed that histone acetylation is induced at switch (S) regions undergoing CSR; however, histone acetylation without accompanying S region transcription is insufficient to attract activation-induced cytidine deaminase (AID), which is required for CSR. They also show that AID can associate with RNA polymerase II. These results support the model that germline transcripts are required to form single-stranded DNA, the AID substrate and further suggest that AID is recruited to S regions by the transcriptional machinery.

Meeting review: options for the control of influenza VI.

A pandemic outbreak of viral influenza could occur if highly virulent zoonotic strains (such as avian H5N1) were to acquire the ability to transmit among humans. This possibility has increased concern, interest, and investigation in the influenza field. This heightened interest was reflected in the participation of numerous health officials, clinicians, and scientific investigators in the Sixth Conference on the Options for the Control of Influenza held in Toronto, Ontario, Canada from June 17-23, 2007. A recurring theme was that H5N1 viruses and the now-available reassortant/recombinant viruses from the 1918 pandemic have striking pathological and molecular similarities. Understanding these similarities, and how the viruses differ from currently circulating strains will be critical for timely preparation of the appropriate vaccines and antiviral therapies if a new pandemic should arise. To that end, this international conference was a fully comprehensive exchange of information covering public health, pandemic planning/preparedness, current and developing vaccines, animal ecology/zoonosis, mathematical modeling, virology, and viral immunology. In this review I will focus on basic research of pathogen-host interactions and immune responses to influenza A virus reported at this conference.

9G4+ antibodies isolated from HIV-infected patients neutralize HIV-1 and have distinct autoreactivity profiles.

Potent HIV-1 specific broadly neutralizing antibodies (BNA) are uncommon in HIV infected individuals, and have proven hard to elicit by vaccination. Several, isolated monoclonal BNA are polyreactive and also recognize self-antigens, suggesting a breach of immune tolerance in persons living with HIV (PLWH). Persons with systemic lupus erythematosus (SLE) often have elevated levels of autoreactive antibodies encoded by the VH4-34 heavy chain immunoglobulin gene whose protein product can be detected by the 9G4 rat monoclonal antibody. We have recently found that levels of these "9G4+" antibodies are also elevated in PLWH. However, the putative autoreactive nature of these antibodies and the relationship of such reactivities with HIV neutralization have not been investigated. We therefore examined the autoreactivity and HIV neutralization potential of 9G4+ antibodies from PLWH. Results show that 9G4+ antibodies from PLWH bound to recombinant HIV-1 envelope (Env) and neutralized viral infectivity in vitro, whereas 9G4+ antibodies from persons with SLE did not bind to Env and failed to neutralize viral infectivity. In addition, while 9G4+ antibodies from PLWH retained the canonical anti-i reactivity that mediates B cell binding, they did not display other autoreactivities common to SLE 9G4+ antibodies, such as binding to cardiolipin and DNA and had much lower reactivity with apoptotic cells. Taken together, these data indicate that the autoreactivity of 9G4+ antibodies from PLWH is distinct from that of SLE patients, and therefore, their expansion is not due to a general breakdown of B cell tolerance but is instead determined in a more disease-specific manner by self-antigens that become immunogenic in the context of, and possibly due to HIV infection. Further studies of 9G4+ B cells may shed light on the regulation of B cell tolerance and interface between the generation of specific autoreactivities and the induction of antiviral immunity in persons living with HIV.

Advances in human B cell phenotypic profiling.

To advance our understanding and treatment of disease, research immunologists have been called-upon to place more centralized emphasis on impactful human studies. Such endeavors will inevitably require large-scale study execution and data management regulation ("Big Biology"), necessitating standardized and reliable metrics of immune status and function. A well-known example setting this large-scale effort in-motion is identifying correlations between eventual disease outcome and T lymphocyte phenotype in large HIV-patient cohorts using multiparameter flow cytometry. However, infection, immunodeficiency, and autoimmunity are also characterized by correlative and functional contributions of B lymphocytes, which to-date have received much less attention in the human Big Biology enterprise. Here, we review progress in human B cell phenotyping, analysis, and bioinformatics tools that constitute valuable resources for the B cell research community to effectively join in this effort.

Multiparameter flow cytometry and bioanalytics for B cell profiling in systemic lupus erythematosus.

B lymphocyte involvement in systemic lupus erythematosus has been recognized for several decades, mainly in the context of autoantibody production. Both mouse and human studies reveal that different types of antibody responses, as well as antibody-independent effector functions can be ascribed to distinct subpopulations (subsets) of circulating B cells. Characterizing human B cell subsets can advance the field of autoimmunity even further by establishing B cell signatures associated with disease severity, progression, and response-to-treatment. For this purpose, we have developed specialized B cell reagent panels for multiparameter flow cytometry, and combine their use with advanced bioinformatics strategies that together will likely be advantageous for improving the characterization, prognosis, and for possibly improving treatment regimens of chronic inflammatory diseases such as lupus.

Antibodies against conserved antigens provide opportunities for reform in influenza vaccine design.

High-performance neutralizing antibody against influenza virus typically recognizes the globular head region of its hemagglutinin (HA) envelope glycoprotein. To-date, approved human vaccination strategies have been designed to induce such antibodies as a sole means of preventing the consequences of this infection. However, frequent amino-acid changes in the HA globular head allow for efficient immune evasion. Consequently, vaccines inducing such neutralizing antibodies need to be annually re-designed and re-administered at a great expense. These vaccines furthermore provide little-to-no immunity against antigenic-shift strains, which arise from complete replacement of HA or of neuraminidase genes, and pose pandemic risks. To address these issues, laboratory research has focused on inducing immunity effective against all strains, regardless of changes in the HA globular head. Despite prior dogma that such cross-protection needs to be induced by cellular immunity alone, several advances in recent years demonstrate that antibodies of other specificities are capable of cross-strain protection in mice. This review discusses the reactivity, induction, efficacy, and mechanisms of antibodies that react with poorly accessible epitopes in the HA stalk, with the matrix 2 membrane ion channel, and even with the internal nucleoprotein. These advances warrant further investigation of the inducibility and efficacy of such revolutionary antibody strategies in humans.

Antibody class switching differs among SJL, C57BL/6 and 129 mice.

Inbred mouse strains used for gene manipulation studies vary in many respects, including immune system function. These differences can interfere with data interpretation unless the mice are well backcrossed. Here, we show that antibody class switching to IgG3 in cultured splenic B cells from Swiss James Lambert (SJL) and 129/Sv mice is 2- to 6-fold less efficient compared with C57BL/6 (B6). Under optimal stimulation conditions, IgA switching is also 2- to 19-fold lower in SJL and 129/Sv B cells. Splenic B cells from SJL mice express higher levels of CD19 and CD21 compared with B6, and their CD21(high)CD23(low) B cells have little CD9 expression, suggesting atypical marginal zone (MZ) B cells. However, sort purification of splenic B cell subsets did not equalize in vitro class switching to IgG3 or IgA between SJL and B6. 129/Sv spleens have a 3-fold greater number of MZ B cells compared with B6, with similar CD9 expression. Poor IgG3 switching by 129/Sv B cells is specific to CD23(high) follicular B cells, whereas similar changes in IgA switching are seen in both CD21(high) and CD23(high) B cell subsets from 129/Sv. Therefore, the functions and phenotypes of mature B cells differ among three common strains of mice.

Stimuli that enhance IgA class switching increase histone 3 acetylation at S alpha, but poorly stimulate sequential switching from IgG2b.

Germ-line (GL) alpha transcription can be induced in mouse splenic B cells by LPS and TGF-beta. This stimulation results in approximately 1% IgA+ cells, which can be increased by IL-4, IL-5, and anti-IgD dextran (alpha delta Dex). To determine the mechanism of this increase, we asked whether IgA class switching correlates with acetylation of histone 3 at S alpha, the switch region for IgA. In the presence of the survival factor B lymphocyte stimulator (BLyS), acetylated histone 3 (AcH3) at S alpha was changed little by TGF-beta in LPS-stimulated mouse splenic B cell cultures, despite induction of GL alpha RNA. Compared with BLyS/LPS/TGF-beta alone, treatment with BLyS/LPS/TGF-beta/IL-4/IL-5/alpha delta Dex increased AcH3 at S alpha fourfold, and also increased GL alpha RNA levels more than eightfold. By contrast, IgG2b class switching was optimal in BLyS/LPS/TGF-beta alone, and was suppressed by IL-4/IL-5/alpha delta Dex. Thus, B cell activators that increase IgA class switching do not increase IgG2b class switching. Further investigation showed that in contrast to purified IgM+ cells, IgG2b+ cells switched poorly to IgA in response to BLyS/LPS/TGF-beta/IL-4/IL-5/ +/- alpha delta Dex. These results suggest that IgA class switching is unusual among isotypes in its requirement for multiple B cell activation signals in addition to LPS and the cytokine that initiates the corresponding GL transcription.

Enhanced IgA class switching in marginal zone and B1 B cells relative to follicular/B2 B cells.

Mouse splenic marginal zone (MZ) B cells and B1 B cells enriched in the peritoneal cavity respond preferentially to T cell-independent Ags compared with follicular (FO)/B2 B cells. Despite the differential responses of B cell subsets to various stimuli, and despite the need for multiple stimuli to induce IgA class switching, the relative contribution of B cell subpopulations to IgA production is unknown. By culturing purified B cell populations, we find that MZ and peritoneal B1 cells switch more readily to IgA than do splenic FO or peritoneal B2 cells in BLyS/LPS/TGF-beta. Addition of IL-4, IL-5, and anti-IgD dextran to the cultures enhances IgA switching in FO/B2 and MZ B cells to a similar frequency, but this treatment suppresses IgA class switching in B1 cells. Thus, IgA switching differs among purified B cell subsets, suggesting that individual B cell populations could contribute differentially to IgA expression in vivo, depending on available stimuli.

The histone methyltransferase Suv39h1 increases class switch recombination specifically to IgA.

Ab class (isotype) switching allows the humoral immune system to adaptively respond to different infectious organisms. Isotype switching occurs by intrachromosomal DNA recombination between switch (S) region sequences associated with C(H) region genes. Although isotype-specific transcription of unrearranged (germline) C(H) genes is required for switching, recent results suggest that isotype specificity is also determined by the sequences of downstream (acceptor) S regions. In the current study, we identify the histone methyltransferase Suv39h1 as a novel Salpha-specific factor that specifically increases IgA switching (Smu-Salpha recombination) in a transiently transfected plasmid S substrate, and demonstrate that this effect requires the histone methyltransferase activity of Suv39h1. Additionally, B cells from Suv39h1-deficient mice have an isotype-specific reduction in IgA switching with no effect on the level of germline Ialpha-Calpha transcripts. Taken together, our results suggest that Suv39h1 activity inhibits the activity of a sequence-specific DNA-binding protein that represses switch recombination to IgA.

Differential regulation of mouse B cell development by transforming growth factor beta1.

Transforming growth factor beta (TGFbeta) can inhibit the in vitro proliferation, survival and differentiation of B cell progenitors, mature B lymphocytes and plasma cells. Here we demonstrate unexpected, age-dependent reductions in the bone marrow (BM) B cell progenitors and immature B cells in TGFbeta1-/- mice. To evaluate TGFbeta responsiveness during normal B lineage development, cells were cultured in interleukin 7 (IL7) +/- TGFbeta. Picomolar doses of TGFbeta1 reduced pro-B cell recoveries at every timepoint. By contrast, the pre-B cells were initially reduced in number, but subsequently increased compared to IL7 alone, resulting in a 4-fold increase in the growth rate for the pre-B cell population. Analysis of purified BM sub-populations indicated that pro-B cells and the earliest BP1- pre-B cells were sensitive to the inhibitory effects of TGFbeta1. However, the large BP1+ pre-B cells, although initially reduced, were increased in number at days 5 and 7 of culture. These results indicate that TGFbeta1 is important for normal B cell development in vivo, and that B cell progenitors are differentially affected by the cytokine according to their stage of differentiation.