MAVS Positively Regulates Mitochondrial Integrity and Metabolic Fitness in B Cells

Activated B cells experience metabolic changes that require mitochondrial remodeling, in a process incompletely defined. In this study, we report that mitochondrial antiviral signaling protein (MAVS) is involved in BCR-initiated cellular proliferation and prolonged survival. MAVS is well known as a mitochondrial-tethered signaling adaptor with a central role in viral RNA-sensing pathways that induce type I IFN. The role of MAVS downstream of BCR stimulation was recognized in absence of IFN, indicative of a path for MAVS activation that is independent of viral infection. Mitochondria of BCR-activated MAVS-deficient mouse B cells exhibited a damaged phenotype including disrupted mitochondrial morphology, excess mitophagy, and the temporal progressive blunting of mitochondrial oxidative capacity with mitochondrial hyperpolarization and cell death. Costimulation of MAVS-deficient B cells with anti-CD40, in addition to BCR stimulation, partially corrected the mitochondrial structural defects and functionality. Our data reveal a (to our knowledge) previously unrecognized role of MAVS in controlling the metabolic fitness of B cells, most noticeable in the absence of costimulatory help.

Plasmodium curtails autoimmune nephritis via lasting bone marrow alterations, independent of hemozoin accumulation

The host response against infection with Plasmodium commonly raises self-reactivity as a side effect, and antibody deposition in kidney has been cited as a possible cause of kidney injury during severe malaria. In contrast, animal models show that infection with the parasite confers long-term protection from lethal lupus nephritis initiated by autoantibody deposition in kidney. We have limited knowledge of the factors that make parasite infection more likely to induce kidney damage in humans, or the mechanisms underlying protection from autoimmune nephritis in animal models. Our experiments with the autoimmune-prone FcγR2B[KO] mice have shown that a prior infection with P. yoelii 17XNL protects from end-stage nephritis for a year, even when overall autoreactivity and systemic inflammation are maintained at high levels. In this report we evaluate post-infection alterations, such as hemozoin accumulation and compensatory changes in immune cells, and their potential role in the kidney-specific protective effect by Plasmodium. We ruled out the role of pigment accumulation with the use of a hemozoin-restricted P. berghei ANKA parasite, which induced a self-resolved infection that protected from autoimmune nephritis with the same mechanism as parasitic infections that accumulated normal levels of hemozoin. In contrast, adoptive transfer experiments revealed that bone marrow cells were altered by the infection and could transmit the kidney protective effect to a new host. While changes in the frequency of bone marrow cell populations after infection were variable and unique to a particular parasite strain, we detected a sustained bias in cytokine/chemokine expression that suggested lower fibrotic potential and higher Th1 bias likely affecting multiple cell populations. Sustained changes in bone marrow cell activation profile could have repercussions in immune responses long after the infection was cleared.

Aedes aegypti sialokinin facilitates mosquito blood feeding and modulates host immunity and vascular biology

Saliva from mosquitoes contains vasodilators that antagonize vasoconstrictors produced at the bite site. Sialokinin is a vasodilator present in the saliva of Aedes aegypti. Here, we investigate its function and describe its mechanism of action during blood feeding. Sialokinin induces nitric oxide release similar to substance P. Sialokinin-KO mosquitoes produce lower blood perfusion than parental mosquitoes at the bite site during probing and have significantly longer probing times, which result in lower blood feeding success. In contrast, there is no difference in feeding between KO and parental mosquitoes when using artificial membrane feeders or mice that are treated with a substance P receptor antagonist, confirming that sialokinin interferes with host hemostasis via NK1R signaling. While sialokinin-KO saliva does not affect virus infection in vitro, it stimulates macrophages and inhibits leukocyte recruitment in vivo. This work highlights the biological functionality of salivary proteins in blood feeding.

CCL17-producing cDC2s are essential in end-stage lupus nephritis and averted by a parasitic infection

Lupus nephritis is a severe organ manifestation in systemic lupus erythematosus leading to kidney failure in a subset of patients. In lupus-prone mice, controlled infection with Plasmodium parasites protects against the progression of autoimmune pathology including lethal glomerulonephritis. Here, we demonstrate that parasite-induced protection was not due to a systemic effect of infection on autoimmunity as previously assumed, but rather to specific alterations in immune cell infiltrates into kidneys and renal draining lymph nodes. Infection of lupus-prone mice with a Plasmodium parasite did not reduce the levels or specificities of autoreactive antibodies, vasculitis, immune complex-induced innate activation, or hypoxia. Instead, infection uniquely reduced kidney-infiltrating CCL17-producing bone marrow-derived type 2 inflammatory dendritic cells (iDC2s). Bone marrow reconstitution experiments revealed that infection with Plasmodium caused alterations in bone marrow cells that hindered the ability of DC2s to infiltrate the kidneys. The essential role for CCL17 in lupus nephritis was confirmed by in vivo depletion with a blocking antibody, which reduced kidney pathology and immune infiltrates, while bypassing the need for parasitic infection. Therefore, infiltration into the kidneys of iDC2s, with the potential to prime local adaptive responses, is an essential regulated event in the transition from manageable glomerulonephritis to lethal tubular injury.

Malaria infection protects from lupus nephritis at a stage beyond immune complex-induced glomerular inflammation

A protective role of malaria infection in SLE was proposed to explain the relatively low prevalence of SLE in West Africa compared to populations of similar genetic background living in the West. Various reports showed an increase of autoantibodies in plasma of West African populations, suggesting that parasite infections were inducing systemic autoreactivity while protecting from tissue pathology. Our own studies from a large longitudinal study in a malaria endemic region confirm the high penetrance of elevated titers of anti-nuclear antibodies in plasma of Plasmodium PCR-positive individuals. In mouse models of malaria, murine Plasmodium infection increases systemic autoreactivity but does not trigger any type of immune-complex induced inflammatory disease. To further investigate the mechanism of kidney protection by Plasmodium, we set up experiments using a malaria parasite in the well characterized SLE mouse model FcγRIIb[KO]. This model system allowed for evaluation of the effect of malaria on autoantibodies, systemic vasculitis and kidney specific pathology, while also assessing the role of parasite-mediated bone marrow alterations, or parasite-produced hemozoin. We found that infection with Plasmodium protects SLE by modifying bone marrow cells and impairing leukocyte infiltration in the kidney, without altering systemic autoimmunity, vasculitis, all independent of the expression of hemozoin. Our results point to a protection of late-stage kidney disease by malaria that targets a step beyond immune complex deposition, hypoxia or innate responses and release of cytokines (IFN, TNF, IL1).

Transcriptional Control of Mature B Cell Fates

The mature naïve B cell repertoire consists of three well-defined populations: B1, B2 (follicular B, FOB), and marginal zone B (MZB) cells. FOB cells are the dominant mature B cell population in the secondary lymphoid organs and blood of both humans and mice. The driving forces behind mature B lineage selection have been linked to B cell receptor (BCR) signaling strength and environmental cues, but how these fate-determination factors are transcriptionally regulated remains poorly understood. We summarize emerging data on the role of transcription factors (TFs) - particularly the ETS and IRF families - in regulating MZB and FOB lineage selection. Indeed, genomic analyses have identified four major groups of target genes that are crucial for FOB differentiation, revealing previously unrecognized pathways that ultimately determine biological responses specific to this lineage.

Antiviral Adaptor MAVS Promotes Murine Lupus With a B Cell Autonomous Role

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by increased production of autoantibodies, which commonly target nuclear antigens, and concomitant deposition of immune complexes that cause inflammation in tissues. SLE is often associated with increased systemic expression of type I interferons, in some cases due to dysregulation in nucleic acid-sensing innate pathways. There is strong genetic evidence for a link between cytoplasmic RNA sensing pathways (RIG-I/MDA5) and SLE, both in human patients and murine models, however questions still remain regarding pathway initiation, cell types involved and downstream effects. Here we show that MAVS, an essential adaptor for RIG-I/MDA5 signaling, is necessary for all symptoms of autoimmune disease that develop spontaneously in the lupus model FcγRIIB^−/− mice. This effect was independent of type I interferon signaling, TLR7 expression or STING, all three factors that have been connected to autoimmunity. Mixed bone marrow reconstitution experiments showed reduced occurrence in autoimmune germinal centers and diminished autoantibody production by MAVS-deficient B cells. Thus, MAVS plays a B cell intrinsic role in autoreactive B cell activation that is independent of its anti-viral functions and independent of elevated type I interferon expression.

Systemic activation of B and CD4 but not CD8 cells drives early disease in lupus prone mice, while macrophages, CD4 and CD8 cells infiltrate the kidney with the exclusion of B cells

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by the presence of autoantibodies in serum and multi-organ inflammation. Immune complex deposition in kidney can lead to lupus nephritis, which is a major risk factor for morbidity and mortality in SLE. Using FcγRIIB−/− mice as a lupus animal model, we performed a detailed time course analysis of the extent of the spontaneous leukocyte activation and expansion in spleen and in renal, inguinal, mesenteric lymph nodes. We then correlated the data with the onset of pathology and leukocyte infiltration in the kidney. In the FcγRIIB−/− mouse model, effector-memory CD4 cells and germinal centers appeared first in the spleen and renal lymph nodes, but not in other immune organs such as inguinal or mesenteric lymph nodes. As the disease progresses in these mice, lymphocytes undergo an extensive expansion that involves all immune organs in a systemic manner. At the same moment we can detect the first signs of kidney pathology, measured by histopathology and by the levels of creatinine and albumin in urine. In FcγRIIB−/− mice, the onset of kidney pathology correlates with leukocyte infiltration in kidney, detected both by parenchyma-restricted flow cytometry and histopathology. Macrophages, CD4 and CD8 cells are found both in glomerular and interstitial spaces with the exclusion of B cells, most likely suggesting a role for T cells and/or macrophage specific chemokine signals in lupus nephritic kidney.

A single infection with a malaria parasite protects mice from lethal autoimmune glomerulonephritis

The progression of autoimmune diseases such as Systemic Lupus Erythematous (SLE) can be altered by environmental factors, including parasitic infections. Epidemiological studies have shown a relative absence of SLE in West Africa (areas of endemic malaria), even though SLE is highly prevalent in populations of African descent living outside of Africa. We hypothesize that malaria infections might reduce the incidence of lupus. In the present work, we assess the effect of the non-lethal Plasmodium yoelii 17XNL in a well-characterized animal model of SLE (FcγRIIB−/−). Mice deficient in the inhibitory Fc receptor for IgG (FcγRIIB) develop spontaneous disease driven by the production of anti-nuclear autoantibodies, a broad immune activation, splenomegaly, anemia and lethal glomerulonephritis with a pathology similar to human SLE. We infected FcγRIIB−/− mice at 2 months of age with P. yoelii and followed the progression of autoimmune disease for 5 months. Infection with P. yoelii increased the titer of a broad range of autoantibodies, with concomitant immune-complex deposition and complement fixation in the kidney. While lupus-prone mice succumbed from renal disease detected by protein in urine, malaria-infected lupus-prone mice did not develop proteinuria or lethal disease. Infection with the parasite did not alter tolerance mechanisms leading to lupus but instead prevented end-point tissue pathology. P. yoelii infection seems to inhibit pathogenic leukocyte infiltration without affecting the autoimmune inflammation of glomeruli. These results indicate a possible route for lupus protection that specifically targets renal function, which remains a cause of the substantial morbidity and mortality in SLE patients.

PU.1 and IRF8 regulate the transcriptional landscapes differently in naïve and activated B cells

The Ets family member PU.1 and the IRF family member IRF8 play crucial roles in regulating hematopoietic cell development including B cells. Both factors are constitutively expressed at high levels in B cells and control plasma cell differentiation. IRF8 and PU.1 function either together as a heterodimer or by pairing with other factors to bind target DNA sequences. Several consensus binding sequences for IRF8 and PU.1 have been identified, including the canonical interferon stimulated response element (ISRE) sequence motif (GAAANNGAAA), the Ets-IRF composite element (EICE) (GGAANNGAAA) and the IRF-Ets composite sequence (IECS) (GAAANN[N]GGAA). Although the target genes of IRF8 and PU.1 have been studied previously by chromatin immunoprecipitation (ChIP), the nature and the importance of the motifs engaging both PU.1 and IRF8 in B cells have not been determined. In this study, we performed ChIP-seq using sort-purified naïve follicular B cells from C57BL/6 mice that were either not stimulated or stimulated with anti-IgM plus anti-CD40, which mimic signals for germinal center B cell differentiation. We also integrated our ChIP-seq data with RNA-seq data from B cells deficient for both IRF8 and PU.1, and found that IRF8 and PU.1 regulate gene expression by preferentially binding to the EICE motifs of target genes known to maintain follicular B cell identity, localization, and survival. In contrast, in activated B cells, the binding landscape of IRF8/PU.1 in target genes shifts to IRF8-dominant ISRE motifs, possibly due to elevated expression of IRF8. These results provide new insights into our understanding of the molecular mechanisms underlying the transcriptional control of late stage B cell development.

VSV-primed CD8+ T cells suppress autoreactive germinal centers

Pathogenic infections are important environmental modifiers of autoimmune disease as they can alter the immune system in a way that either promotes or reduces autoimmune responses. We tested the effect of infection with vesicular stomatitis virus (VSV) on the FcγR2B−/− (R2) mouse strain that spontaneously develops lupus disease. Infecting FcγR2B−/− mice with live VSV reduces autoantibody levels and inflammatory pathology and prolongs survival. We showed that VSV-mediated protection can be transferred in a CD8 cell adoptive transfer experiment. After further testing the transfer of various CD8 T cell subsets, we have identified CD8+CD122+NKG2D+ cells as mediator in VSV-induced Lupus amelioration. RNA Sequencing data for gene expression profiles among various CD8 subsets, indicate that the protective cells express higher level of genes linked to memory phenotype. Our working hypothesis is that the viral infection may induce the expansion of long lived CD8 populations that regulate the antibody response.

In support of the idea we initiated to identify the target of the VSV-primed CD8 T cells in vivo. We examined the effect of VSV-primed CD8 T cells on the immune phenotypes of recipient R2 mice at the initial stages, e.g. after 1, 2 or 3 weeks of transfer. Interestingly, we found that Tfh and germinal center B cells are significantly reduced after three weeks of VSV-CD8 transfer. Thus, the protective CD8 T cells from VSV-infected mice might target autoreactive germinal center to regulate the antibody response. How VSV-CD8 T cells might control germinal center & why it takes about 3 weeks for controlling is under investigation.

Strong Selection of a Few Dominant CD8 Clones in a TLR7-Dependent Autoimmune Mouse Model

Systemic lupus is characterized by the expansion of a self-reactive repertoire of B cells and CD4 cells that together promote IgG Ab production against common nuclear Ags. Although several studies have suggested roles for CD8⁺ T cells in lupus, the full contribution of these lymphocytes to disease remains undefined. In particular, few studies have examined TCR clonotypes of the CD8 pool in lupus. We previously described activated but nonpathogenic CD8⁺ T cells in a mouse model of systemic autoimmune disease triggered by increased copy number of the tlr7 gene (TLR7tg mice), in which some of these T cells accumulate in the brain. In this article, we report, through the analysis of TCRβ sequences, that CD8 cells from TLR7tg animals are strongly selected for a small number of clones, some of them reaching 30% of the repertoire, compared with less than 0.4% for the top clone in any wild type mice. High frequency clones are variable in sequence among individual TLR7tg mice and are distinct from top clones in the control animals, whereas CDR3 sequences of spleen and brain-resident T cells from the same TLR7tg animals have perfect concordance. These results suggest that top CD8 clones are selected in stochastic fashion in each animal but limit further diversification, and that brain-infiltrating CD8 cells in TLR7tg mice are not selected by a common tissue Ag. This kind of extreme clonal dominance and narrowing of the CD8⁺ repertoire might impair anti-viral responses and should be considered as an additional detrimental feature of chronic autoimmune disease.

Lupus-suppressing effect of VSV-primed CD8+ T cell subsets

Pathogenic infections are important environmental modifiers of autoimmune disease as they can alter the immune system in a way that either promotes or reduces autoimmune responses. We tested the effect of infection with vesicular stomatitis virus (VSV) on the FcγR2B−/− (R2) mouse strain that spontaneously develops lupus disease. Infecting FcγR2B−/− mice with live VSV reduces autoantibody levels and inflammatory pathology, and prolongs survival. We showed that VSV-mediated protection can be transferred in a CD8 cell adoptive transfer experiment. Legend screening for surface markers on CD8 T cells indicated that CD8 T cells from VSV infected mice express high level of markers linked to exhausted and regulatory phenotypes. After testing the transfer of various CD8 T cell subsets, we have identified CD8+CD122+NKG2D+ cells as mediator in VSV-induced Lupus amelioration. Preliminary analysis of RNA Sequencing data for gene expression profiles among various CD8 subsets, indicate that the protective cells express higher level of genes linked to memory phenotype. Our working hypothesis is that the viral infection may induce the expansion of long lived CD8 populations that regulate the humoral response.

A single infection with a malaria parasite protects mice from lethal autoimmune glomerulonephritis

Infections can alter the prevalence of autoimmune diseases such as SLE. Epidemiological studies have showed a relative absence SLE in West Africa (areas of endemic malaria), even though SLE is highly prevalent in populations of African descent living outside of Africa. We hypothesize that malaria infections might reduce the incidence of autoimmune lupus. In the present work, we assess the effect of the non-lethal Plasmodium yoelii 17XNL in a well-characterized animal model of SLE (FcγRIIB−/−). Mice deficient in the inhibitory Fc receptor for IgG (FcγRIIB) develop spontaneous disease driven by the production of anti-nuclear autoantibodies, a broad immune activation, splenomegaly, anemia and lethal glomerulonephritis with a pathology similar to human SLE. We infected FcγRIIB−/− mice at 2 months of age with P.yoelii and followed the progression of autoimmune disease for 5 months. Infection with P. yoelii increased the titer of a broad range of autoantibodies, with concomitant immune-complex deposition and complement fixation in the kidney. While lupus-prone mice succumbed from renal disease detected by protein in urine and serum urea nitrogen, malaria-infected lupus-prone mice did not develop proteinuria or lethal disease. Infection with the parasite did not alter tolerance mechanisms leading to lupus but instead prevented end-point tissue pathology. P. yoelii infection seems to inhibit pathogenic leukocyte infiltration without affecting the autoimmune inflammation of glomeruli. These results indicate a possible route for lupus protection that specifically targets renal function, which remains a cause of the substantial morbidity and mortality in SLE patients.

The Csk-Associated Adaptor PAG Inhibits Effector T Cell Activation in Cooperation with Phosphatase PTPN22 and Dok Adaptors

The transmembrane adaptor PAG (Cbp) has been proposed to mediate membrane recruitment of Csk, a cytoplasmic protein tyrosine kinase playing a critical inhibitory role during T cell activation, by inactivating membrane-associated Src kinases. However, this model has not been validated by genetic evidence. Here, we demonstrate that PAG-deficient mice display enhanced T cell activation responses in effector, but not in naive, T cells. PAG-deficient mice also have augmented T cell-dependent autoimmunity and greater resistance to T cell anergy. Interestingly, in the absence of PAG, Csk becomes more associated with alternative partners; i.e., phosphatase PTPN22 and Dok adaptors. Combining PAG deficiency with PTPN22 or Dok adaptor deficiency further enhances effector T cell responses. Unlike PAG, Cbl ubiquitin ligases inhibit the activation of naive, but not of effector, T cells. Thus, Csk-associating PAG is a critical component of the inhibitory machinery controlling effector T cell activation in cooperation with PTPN22 and Dok adaptors.

T cell-dependent antigen adjuvanted with DOTAP-CpG-B but not DOTAP-CpG-A induces robust germinal center responses and high affinity antibodies in mice

The development of vaccines for infectious diseases for which we currently have none, including HIV, will likely require the use of adjuvants that strongly promote germinal center responses and somatic hypermutation to produce broadly neutralizing antibodies. Here we compared the outcome of immunization with the T-cell dependent antigen, NP-conjugated to chicken gamma globulin (NP-CGG) adjuvanted with the toll-like receptor 9 (TLR9) ligands, CpG-A or CpG-B, alone or conjugated with the cationic lipid carrier, DOTAP. We provide evidence that only NP-CGG adjuvanted with DOTAP-CpG-B was an effective vaccine in mice resulting in robust germinal center responses, isotype switching and high affinity NP-specific antibodies. The effectiveness of DOTAP-CpG-B as an adjuvant was dependent on the expression of the TLR9 signaling adaptor MyD88 in immunized mice. These results indicate DOTAP-CpG-B but not DOTAP-CpG-A is an effective adjuvant for T cell-dependent protein antigen-based vaccines.

B Cells Produce Type 1 IFNs in Response to the TLR9 Agonist CpG-A Conjugated to Cationic Lipids

B cells express the innate receptor, TLR9, which signals in response to unmethylated CpG sequences in microbial DNA. Of the two major classes of CpG-containing oligonucleotides, CpG-A appears restricted to inducing type 1 IFN in innate immune cells and CpG-B to activating B cells to proliferate and produce Abs and inflammatory cytokines. Although CpGs are candidates for adjuvants to boost innate and adaptive immunity, our understanding of the effect of CpG-A and CpG-B on B cell responses is incomplete. In this study we show that both CpG-B and CpG-A activated B cells in vitro to proliferate, secrete Abs and IL-6, and that neither CpG-B nor CpG-A alone induced type 1 IFN production. However, when incorporated into the cationic lipid, DOTAP, CpG-A, but not CpG-B, induced a type 1 IFN response in B cells in vitro and in vivo. We provide evidence that differences in the function of CpG-A and CpG-B may be related to their intracellular trafficking in B cells. These findings fill an important gap in our understanding of the B cell response to CpGs, with implications for the use of CpG-A and CpG-B as immunomodulators.

Non-pathogenic CD8+ T cells in lupus-prone mice regulate neurological and peripheral disease

Lupus is a systemic autoimmune disorder affecting multiple organ systems including the skin, kidneys, spleen, lungs, and brain. Severe SLE often manifests with multiple psychiatric and neurological sequelae, and may be accompanied by CNS vasculitis. However, the cellular contributors to CNS disease in lupus patients remain poorly defined. We have uncovered a unique bias for CD8+ T cell infiltration in the CNS of mice expressing multiple copies of Toll-like receptor 7 (TLR7[Tg]), which present with a lupus-like disease. These animals exhibit blood brain barrier damage and neuropathology in the presence of infiltrating T cells. However, genetic ablation of CD8+ T cells in lupus-prone mice by removal of the major histocompatibility complex (MHC) adaptor protein b2m results in aggravation of disease, suggesting the removal of a protective population. Relative to the peripheral CD8+ T cells in lupus-prone mice, those in the CNS represent the most activated lymphocytes in the animal, display a tissue resident-memory phenotype, and can home to the brain. We have also identified a population of CD8+ T cells in the cerebrospinal fluid (CSF) of several lupus patients. Similar to our animal model findings the human CD8+ T cells in the CSF have a large increase in antigen experience by surface phenotyping relative to lymphocytes from peripheral blood. Our ongoing studies aim to elucidate specifically how these CD8+ T cells enter the CNS and further clarify their role in neuropathology. Our findings suggest a possible mechanism of CNS pathology regulation that could have applicability to human neuropsychiatric manifestations of SLE.

The Toll-like receptor ligand CpG-A induces type 1 interferons in B cells contrasting the proinflammatory inducing activity of CpG-B

B cells express the innate immune system receptor, Toll like receptor 9 (TLR9), a potent regulator of B cell function, that signals in response to unmethylated CpG sequences in microbial DNA. A dichotomy in the function of the two major classes of CpG-containing oligonucleotides, namely CpG-A and CpG-B, appears to exist with CpG-A restricted to inducing type 1 interferon (type 1 IFN) in innate immune cells and CpG-B to activating B cells to proliferate and produce antibody and inflammatory cytokines. Although CpGs are candidates for adjuvants to boost the innate and adaptive immunity, our understanding of the effect of CpG-A and CpG-B on B cell responses is incomplete. We provide evidence that CpG-A activated B cells in vitro in a TLR9 dependent fashion resulting in the production of IL-6, proliferation, and alterations in the expression of a variety of B cell surface markers, albeit in a less robust fashion as compared to CpG-B. Neither CpGB nor CpG-A alone induced B cells to express type 1 IFN. However, when incorporated into the cationic lipid, DOTAP, CpG-A, but not CpG-B induced a robust type 1 IFN response in B cells both in vitro and in vivo. Conversely, CpG-B-DOTAP but not CpGA-DOTAP promoted B cell germinal center responses in vivo and the production of high affinity antibodies. We also provide evidence that difference in the function of CpGs versus DOTAP-associated-CpGs may be related to their intracellular trafficking in B cells since DOTAP enhances the trafficking of CpG-B but not CpG-A to late endosomal compartments. These findings have important implications for the use of CpG-A and CpG-B to augment type 1 IFN production versus B cell responses in vivo.

Autoimmune responses are dependent on the MAVS innate pathway due to its natural co-stimulating effect on B cell activation and maturation

There is evidence that autoimmune disease might be induced by deficient regulation of innate immune pathways that normally induce type I interferon in response to pathogen-derived nucleic acids. To investigate a potential role for nucleic acid sensing pathways with cytosolic localization and more ubiquitous expression, we tested the requirement for MAVS (dsRNA-sensing) or STING (dsDNA-sensing) in the lupus autoimmune disease developed by FcγRIIB-KO (R2−/−) mice. These experiments revealed that STING was mildly protective, while MAVS was an essential factor for autoimmune disease in R2−/− mice. We found that MAVS deficiency, but not type I IFN receptor deficiency, completely eliminated autoantibodies and autoimmune pathology in R2−/− mice. MAVS deficiency also eliminated spontaneous activation of B and T cells, germinal center formation and follicular helper T cell development. Using mixed bone marrow reconstitution experiments, we determined that MAVS was required for autoreactivity in a B cell intrinsic manner, with a profound effect on B cell survival in the germinal center. MAVS deficiency did not alter BCR-proximal signaling, but resulted in diminished long term proliferative capacity of B cells, with lower cyclin D2 and Bcl-xL expression 24 hours after anti-IgM stimulation. MAVS deficiency also resulted in B cell developmental defects, fewer total B cells but a skewing toward marginal zone and against the follicular B cell program. Overall MAVS seems to provide its costimulatory effect independent of type I IFN, by enhancing the activation of NFκB in situations where T cell help or other modes of costimulation are not present and most importantly, by providing survival stimulus for autoreactive B cells.

Identification of a suppressor of autoimmune phenotype that affects deoxynucleotide synthesis in T cells

FcγRIIB-deficient mice represent a well-characterized animal model of systemic lupus erythematosus. They develop spontaneous anti-nuclear antibodies (ANA) and fatal glomerulonephritis when on the C57BL/6 (B6) background while the same mutation on the BALB/c background is phenotypically benign, indicating differences in lupus susceptibility between the BALB/c and B6 strains. We mapped the BALB/c derived protection to a 151KB genomic fragment on chromosome 12. Insertion of this fragment in transgenic form (A12Tg) results in protection from lupus disease. Mixed bone marrow reconstitution experiments pointed to a T cell intrinsic effect of the protective gene in the BALB/c A12 interval. This region contains a single gene, Rrm1, which encodes for a subunit of the ribonucleotide reductase responsible for the synthesis of deoxiribonucleotides. We hypothesize that reduced levels of this enzyme affect the ability of T cell to expand upon activation and that is why allelic differences in Rrm2 expression can alter tolerance in mouse models of lupus.

Expanding the B Cell-Centric View of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by a breakdown of self-tolerance in B cells and the production of antibodies against nuclear self-antigens. Increasing evidence supports the notion that additional cellular contributors beyond B cells are important for lupus pathogenesis. In this review we consider recent advances regarding both the pathogenic and the regulatory role of lymphocytes in SLE beyond the production of IgG autoantibodies. We also discuss various inflammatory effector cell types involved in cytokine production, removal of self-antigens, and responses to autoreactive IgE antibodies. We aim to integrate these ideas to expand the current understanding of the cellular components that contribute to disease progression and ultimately help in the design of novel, targeted therapeutics.

Brain infiltrating CD8+ T lymphocytes in lupus-prone mice

Systemic lupus erythematosus (SLE) is an autoimmune disorder affecting multiple organ systems including the skin, kidneys, spleen, lungs, and brain. Severe SLE often manifests with multiple psychiatric and neurological sequelae, and may be accompanied by CNS vasculitis. However, the cellular contributors to CNS disease in lupus patients remain poorly defined. Our data demonstrate a unique lymphocyte bias in the CNS of mice expressing multiple copies of Toll-like receptor 7 (TLR7[Tg], FcgRIIB-Yaa), which present with a lupus-like disease. Lupus-prone mice have a substantial population of infiltrating CD8+ T cells in the CNS, a bias that is not present in other peripheral lymphoid or non-lymphoid tissues. These animals exhibit blood-brain barrier damage and neuropathology in the presence of the infiltrating lymphocytes. However, genetic ablation of CD8+ T cells in lupus-prone mice by removal of the major histocompatibility complex (MHC) adaptor protein b2m results in aggravation of disease, suggesting the removal of a protective population. Circulating CD8+ T cells in lupus-prone mice display an activated phenotype, express a number of surface trafficking and adhesion molecules, and can home to the CNS. The endothelium of the brain, but not of other peripheral organs in these mice is activated, expressing adhesion markers complementary to those found on infiltrating CD8+ T cells. Our ongoing studies aim to elucidate specifically how these CD8+ T cells enter the CNS and further clarify their role in neuropathology. Our findings suggest a possible mechanism regulating CNS pathology that could have applicability to human neuropsychiatric manifestations of SLE.

B cell autophagy mediates TLR7-dependent autoimmunity and inflammation

Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease, defined by loss of B cell self-tolerance that results in production of antinuclear antibodies (ANA) and chronic inflammation. While the initiating events in lupus development are not well defined, overexpression of the RNA-recognizing toll-like receptor (TLR)7 has been linked to SLE in humans and mice. We postulated that autophagy plays an essential role in TLR7 activation of B cells for the induction of SLE by delivering RNA ligands to the endosomes, where this innate immune receptor resides. To test this hypothesis, we compared SLE development in Tlr7 transgenic (Tg) mice with or without B cell-specific ablation of autophagy (Cd19-Cre Atg5(f/f)). We observed that in the absence of B cell autophagy the 2 hallmarks of SLE, ANA and inflammation, were eliminated, thus curing these mice of lupus. This was also evident in the significantly extended survival of the autophagy-deficient mice compared to Tlr7.1 Tg mice. Furthermore, glomerulonephritis was ameliorated, and the serum levels of inflammatory cytokines in the knockout (KO) mice were indistinguishable from those of control mice. These data provide direct evidence that B cells require TLR7-dependent priming through an autophagy-dependent mechanism before autoimmunity is induced, thereafter involving many cell types. Surprisingly, hyper-IgM production persisted in Tlr7.1 Tg mice in the absence of autophagy, likely involving a different activation pathway than the production of autoantibodies. Furthermore, these mice still presented with anemia, but responded with a striking increase in extramedullary hematopoiesis (EMH), possibly due to the absence of pro-inflammatory cytokines.

Abstract 2075: Signaling thresholds and negative B cell selection in acute lymphoblastic leukemia

Introduction: Unlike other cell types, B cells are selected for an intermediate level of signaling strength. Critical survival and proliferation signals emanate from the (pre-) B cell receptor (BCR): Both attenuation below minimum (e.g. non-functional pre-BCR) and hyperactivation above maximum (e.g. autoreactive pre-BCR) thresholds of signaling strength trigger negative selection and cell death. The oncogenic BCR-ABL1 tyrosine kinase mimics active pre-BCR signaling in Ph+ acute lymphoblastic leukemia (ALL) which defines the ALL subgroup with the worst clinical outcome. Current therapy approaches are largely focused on the development of more potent tyrosine kinase inhibitors (TKI) to suppress oncogenic signaling. However resistance to TKI is developed invariably. Here, we test the hypothesis that targeting hyperactivation above a maximum threshold will selectively kill Ph+ ALL cells, similar to removal of self-reactive B cells.

Results: The Ph+ ALL cells don not express ITAM (immunoreceptor tyrosine-based activation motif) receptor Igα or Igβ on the cell surface, indicating defects for a functional pre-BCR. Reconstitution of ITAM receptor was sufficient to induce cell death through increasing pre-BCR signaling strength indicated by phosphorylation of SYK, SRC, BTK and PLCγ2. TKI-treatment, while designed to kill leukemia cells, seemingly paradoxically rescued Ph+ ALL cells in this experimental setting. Surprisingly, patient-derived Ph+ ALL cells express the ITIM (immunoreceptor tyrosine-based inhibitory motif) receptors PECAM1, CD300A and LAIR1 at high levels compared to normal pre-B cells. Importantly, high expression levels of ITIM-receptors are predictive of poor outcome in two clinical trials, including both pediatric and adult ALL patients. Genetic studies revealed that Pecam1, Cd300a and Lair1 were critical to calibrate pre-BCR signaling strength through recruitment of the inhibitory phosphatases Ptpn6 (Shp1) and Inpp5d (Ship1). Genetic deletion of Lair1, Ptpn6 or Inpp5d in BCR-ABL1 ALL caused cell death in vitro and in vivo through hyperactivation of pre-BCR signaling. Testing various components of proximal pre-BCR signaling, we found that an incremental increase of SYK tyrosine kinase activity was required and sufficient to induce cell death. Hyperactive SYK was functionally equivalent to acute activation of a self-reactive BCR on ALL cells. Using chimeric PECAM1, CD300A and LAIR1 receptor decoys and a novel small molecule inhibitor of INPP5D, we demonstrated that pharmacological hyperactivation of pre-BCR signaling and engagement of negative B cell selection represents a promising new strategy to overcome drug-resistance in human Ph+ ALL.

Conclusion: These results indicated that inhibitory receptors and downstream phosphatases are critical regulators of pre-BCR signaling strength in Ph+ ALL, and identified targeting hyperactivation of pre-BCR signaling as a potential novel class of therapeutic strategy.

Note: This abstract was not presented at the meeting.

Citation Format: Zhengshan Chen, Seyedmehdi Shojaee, Maike Buchner, Huimin Geng, Jae Woong Lee, Lars Klemm, Eugene Park, Ying Xim Tan, Anne Satterthwaite, Elisabeth Paietta, Stephen P. Hunger, Mignon L. Loh, Jae U. Jung, John E. Coligan, Silvia Bolland, Tak W. Mak, Andre Limnander, Hassan Jumaa, Michael Reth, Arthur Weiss, Clifford A. Lowell, Markus Müschen. Signaling thresholds and negative B cell selection in acute lymphoblastic leukemia. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2075. doi:10.1158/1538-7445.AM2015-2075

Cutting Edge: Induction of Inflammatory Disease by Adoptive Transfer of an Atypical NK Cell Subset

Several mouse models of systemic lupus erythematosus, including FcγRIIB-KO and TLR7tg mice, develop an expansion of an atypical NK cell subset with functional similarity to cells referred as IFN-producing killer DCs or pre-mature NKs in other systems. In this study, we show that atypical NKs purified from spleens of systemic lupus erythematosus-prone mice, and identified as NK1.1(+)CD11c(+)CD122(+)MHC-II(+), induce persistent autoimmune disease in an IFN-I- and CD40L-dependent manner when transferred to wild-type mice. A single transfer of 4 × 10(6) NK1.1(+) cells from TLR7tg into wild-type induces a 2-wk-long wave of inflammatory cytokines in the serum; a sustained increase in T cell activation and follicular helper cells for the following months; and a progressive expansion of dendritic cells, monocytes, and granulocytes. Furthermore, IL-15 deficiency, which impedes development of NK cells, ameliorates the autoimmune pathology of TLR7tg mice. These results suggest that cells of the NK lineage can develop into cytokine-producing/APCs that affect the priming and progression of systemic autoimmune disease.

Signalling thresholds and negative B-cell selection in acute lymphoblastic leukaemia

B cells are selected for an intermediate level of B-cell antigen receptor (BCR) signalling strength: attenuation below minimum (for example, non-functional BCR) or hyperactivation above maximum (for example, self-reactive BCR) thresholds of signalling strength causes negative selection. In ∼25% of cases, acute lymphoblastic leukaemia (ALL) cells carry the oncogenic BCR-ABL1 tyrosine kinase (Philadelphia chromosome positive), which mimics constitutively active pre-BCR signalling. Current therapeutic approaches are largely focused on the development of more potent tyrosine kinase inhibitors to suppress oncogenic signalling below a minimum threshold for survival. We tested the hypothesis that targeted hyperactivation--above a maximum threshold--will engage a deletional checkpoint for removal of self-reactive B cells and selectively kill ALL cells. Here we find, by testing various components of proximal pre-BCR signalling in mouse BCR-ABL1 cells, that an incremental increase of Syk tyrosine kinase activity was required and sufficient to induce cell death. Hyperactive Syk was functionally equivalent to acute activation of a self-reactive BCR on ALL cells. Despite oncogenic transformation, this basic mechanism of negative selection was still functional in ALL cells. Unlike normal pre-B cells, patient-derived ALL cells express the inhibitory receptors PECAM1, CD300A and LAIR1 at high levels. Genetic studies revealed that Pecam1, Cd300a and Lair1 are critical to calibrate oncogenic signalling strength through recruitment of the inhibitory phosphatases Ptpn6 (ref. 7) and Inpp5d (ref. 8). Using a novel small-molecule inhibitor of INPP5D (also known as SHIP1), we demonstrated that pharmacological hyperactivation of SYK and engagement of negative B-cell selection represents a promising new strategy to overcome drug resistance in human ALL.

Linking susceptibility genes and pathogenesis mechanisms using mouse models of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) represents a challenging autoimmune disease from a clinical perspective because of its varied forms of presentation. Although broad-spectrum steroids remain the standard treatment for SLE, they have many side effects and only provide temporary relief from the symptoms of the disease. Thus, gaining a deeper understanding of the genetic traits and biological pathways that confer susceptibility to SLE will help in the design of more targeted and effective therapeutics. Both human genome-wide association studies (GWAS) and investigations using a variety of mouse models of SLE have been valuable for the identification of the genes and pathways involved in pathogenesis. In this Review, we link human susceptibility genes for SLE with biological pathways characterized in mouse models of lupus, and discuss how the mechanistic insights gained could advance drug discovery for the disease.

Induction of autoimmune disease by adoptive transfer of an atypical NK cell subset (BA7P.147)

Several mouse models of SLE, including FcgRIIB-KO and TLR7tg mice, develop an expansion of an atypical NK cell subset with functional similarity to cells referred as IKDCs or pre-mNKs in other systems and identified as NK1.1+CD11c+CD122+MHC-II+. These cells belong to the NK cell lineage because they depend on IL15 and express E4BP4. Functionally they are cytotoxic, produce type I and type II interferons upon activation and they are efficient antigen presenting cells both through MHC-II expression and in cross-presentation to CD8s. These atypical NK cells are responsive to TLR stimulation and thus are most abundant in mice with high copy number of the Tlr7 gene. They are highly proliferative as assessed by in vivo BrdU incorporation. Transferring 4 million atypical NKs purified from spleens of SLE-prone mice into WT induces a 2-week-long wave of inflammatory cytokines in the serum, a sustained increase in T cell activation and follicular helper cells for the following months, and a progressive expansion of dendritic cells, monocytes and granulocytes. Furthermore IL15 deficiency, which impedes development of NK cells, ameliorates the autoimmune pathology of TLR7tg mice. These results suggest that cells of the NK lineage can develop into cytokine producing/antigen-presenting cells that affect the priming and progression of systemic autoimmune disease.

Ups and downs in the search for a Herpes simplex virus vaccine

Modified herpes simplex viruses that are unable to produce glycoprotein D may make effective vaccines.

Expansion of an atypical NK cell subset in mouse models of systemic lupus erythematosus

Chronic inflammatory conditions, such as in autoimmune disease, can disturb immune cell homeostasis and induce the expansion of normally rare cell populations. In our analysis of various murine models of lupus, we detect increased frequency of an uncommon subset identified as NK1.1(+)CD11c(+)CD122(+)MHC class II(+). These cells share characteristics with the NK cell lineage and with cells previously described as IFN-producing killer dendritic cells: 1) they depend on IL-15 and express E4BP4; 2) they are cytotoxic and produce type I and type II IFN upon activation; and 3) they are efficient APCs both through MHC class II expression and in cross-presentation to CD8s. These atypical NK cells are responsive to TLR stimulation and thus are most abundant in mice with high copy number of the Tlr7 gene. They are highly proliferative as assessed by in vivo BrdU incorporation. In adoptive transfer experiments they persist in high numbers for months and maintain their surface marker profile, indicating that this population is developmentally stable. Gene expression analyses on both mRNA and microRNAs show a modified cell cycle program in which various miR-15/16 family members are upregulated, presumably as a consequence of the proliferative signal mediated by the increased level of growth factors, Ras and E2F activity. Alternatively, low expression of miR-150, miR-181, and miR-744 in these cells implies a reduction in their differentiation capacity. These results suggest that cells of the NK lineage that undergo TLR stimulation might turn on a proliferative program in detriment of their full differentiation into mature NK cells.

Immunoglobulin E plays an immunoregulatory role in lupus

The (patho)physiological role of IgE in nonallergic inflammatory diseases is not well understood. Here, we explored the effect of IgE deficiency on the inflammatory response in FcγRIIB-deficient mice as well as in mice carrying both a deletion of FcγRIIB and the chromosomal translocation of Y-linked autoimmune acceleration (Yaa) that hastens and results in a more aggressive lupuslike disease in these mice. The findings show that deficiency of IgE delays disease development and severity as demonstrated by reduced autoantibody production and amelioration of organ pathologies. This was associated with decreased numbers of plasma cells and reduced levels of IgG2b and IgG3. Unexpectedly, the loss of IgE also caused a striking decrease of immune cell infiltration in secondary lymphoid organs with a marked effect on the presence of dendritic cells, monocytes, neutrophils, and eosinophils in these organs and decreased activation of basophils. The presence of autoreactive IgE in human systemic lupus erythematosus subjects was also associated with increased basophil activation and enhanced disease activity. These findings argue that IgE facilitates the amplification of autoimmune inflammation.

Genetic evidence for the role of plasmacytoid dendritic cells in systemic lupus erythematosus

Genetic impairment of plasmacytoid dendritic cells ameliorates autoantibody production and symptoms of SLE in mice.

Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by the production of antibodies to self-nucleic acids, immune complex deposition, and tissue inflammation such as glomerulonephritis. Innate recognition of self-DNA and -RNA and the ensuing production of cytokines such as type I interferons (IFNs) contribute to SLE development. Plasmacytoid dendritic cells (pDCs) have been proposed as a source of pathogenic IFN in SLE; however, their net contribution to the disease remains unclear. We addressed this question by reducing gene dosage of the pDC-specific transcription factor E2-2 (Tcf4), which causes a specific impairment of pDC function in otherwise normal animals. We report that global or DC-specific Tcf4 haplodeficiency ameliorated SLE-like disease caused by the overexpression of the endosomal RNA sensor Tlr7. Furthermore, Tcf4 haplodeficiency in the B6.Sle1.Sle3 multigenic model of SLE nearly abolished key disease manifestations including anti-DNA antibody production and glomerulonephritis. Tcf4-haplodeficient SLE-prone animals showed a reduction of the spontaneous germinal center reaction and its associated gene expression signature. These results provide genetic evidence that pDCs are critically involved in SLE pathogenesis and autoantibody production, confirming their potential utility as therapeutic targets in the disease.

B cell autophagy mediates TLR7-dependent SLE and controls extramedullary hematopoiesis (BA4P.217)

Systemic Lupus Erythematosus (SLE) is a heterogeneous disease, defined by a loss of B cell self-tolerance resulting in the production of autoantibodies. One of the many mechanisms described resulting in a break in B cell self-tolerance is overexpression of the endosomal toll-like receptor, TLR7. We hypothesized that autophagy plays a crucial role in TLR7 activation in B cells by delivering ligand to endosomes. To test this model, we produced TLR7 transgenic (tg) mice with a B cell-specific (CD19-cre) ablation of autophagy (ATG5 ko), and compared SLE development to that of TLR7 tg mice with intact autophagy machinery. We observed that loss of ATG5 in B cells significantly increased the survival of TLR7 tg mice, reduced serum IgG and anti-nuclear autoantibodies, thereby preventing glomerulonephritis. These data suggest that B cell autophagy is required for TLR7-mediated SLE disease progression. However, while symptoms of SLE were ameliorated, extramedullary hematopoiesis (EMH) was dramatically increased with a splenic red pulp expansion in these mice. Thus, autophagy in B cells plays an important role in controlling lineage determination in hematopoiesis, likely by regulating chemokine and cytokine production, the mechanism by which is currently under investigation. A better understanding of the control steps involved in TLR7 activation and cytokine production could lead to improved therapeutics for treatment of SLE.

Understanding lupus pathology in FcγRIIB-/-yaa mice: autoantibodies and autoantigens (P4008)

FcγRIIB knock-out mice in B6 background develop a lupus like autoimmune disease. With the addition of the yaa (Y-chromosome autoimmune accelerator) gene, pathogenecity in these male mice is significantly enhanced and autoantibodies switch from nuclear to nucleolar specificity. High titer of λ-light chains immunoglobulin, and anti-RNA antibodies were found in R2-/-yaa serum. Also, R2-/-yaa serum selectively bound 5 major nuclear proteins compared to R2-/- serum. To characterize the autoantibodies produced by R2-/-yaa mice and the nucleolar antigens that react with these antibodies, we have produced hybridomas. Hybridoma H526 produced anti-nucleolar IgG2c-λ antibodies. The antibody binds RNA, a synthetic polyribonucleotide poly (GC)20 and a RNA-associated nucleolar protein, nucleolin. R2-/-yaa serum also found to cross-react with poly (GC)20, nucleolin and also with poly ADP-ribose (PAR). Simultaneous presence of nucleolin and PAR autoantibodies has been found to be associated with lupus. Further characterization of nucleolin modification and lupus development is in progress.

Autophagy: a dichotomous player in Toll-like receptor 7-mediated autoimmunity. (P4073)

The endosomal Toll-like receptor, TLR7, acts as critical line of defense against viral pathogens; however, overexpression of TLR7 has been shown to lead to spontaneous lupus-like disease (SLE). Thus, tight regulation of this pattern recognition receptor is crucial in preventing a hyperactive cellular state. We hypothesized that autophagy plays a role in TLR7 activation by delivering ligand to endosomes and by controlling subsequent inflammatory responses. To test this model, we crossed TLR7 transgenic (tg) mice that succumb to SLE with mice where ATG5, a critical autophagy gene, was deleted in dendritic cells (DCs) or B cells or both. These mice were compared to TLR7 tg mice with intact autophagy for morbidity and the inflammatory response. We observed that loss of ATG5 in either DCs or B cells significantly increased the survival of TLR7 tg mice, while ATG5 deletion in both cell types only modestly improved survival. On the other hand, loss of autophagy led to an elevated inflammatory response compared to TLR7 tg mice with intact autophagy, as evidenced by vastly increased lymphoid organ mass and elevated numbers of granulocytes and macrophages. The inflammatory mediators involved in this process are currently under investigation. These data suggest that autophagy plays an important and dichotomous role in TLR7-mediated autoimmunity, both enabling and ameliorating symptoms of SLE. It is likely that autophagy is affecting multiple TLR7-dependent signaling processes.

Increased ribonuclease expression reduces inflammation and prolongs survival in TLR7 transgenic mice

TLR7 activation is implicated in the pathogenesis of systemic lupus erythematosus. Mice that overexpress TLR7 develop a lupus-like disease with autoantibodies and glomerulonephritis and early death. To determine whether degradation of the TLR7 ligand RNA would alter the course of disease, we created RNase A transgenic (Tg) mice. We then crossed the RNase Tg to TLR7 Tg mice to create TLR7 × RNase double Tg (DTg) mice. DTg mice had a significantly increased survival associated with reduced activation of T and B lymphocytes and reduced kidney deposition of IgG and C3. We observed massive hepatic inflammation and cell death in TLR7 Tg mice. In contrast, hepatic inflammation and necrosis were strikingly reduced in DTg mice. These findings indicate that high concentrations of serum RNase protect against immune activation and inflammation associated with TLR7 stimulation and that RNase may be a useful therapeutic strategy in the prevention or treatment of inflammation in systemic lupus erythematosus and, possibly, liver diseases.

Aberrant antibody affinity selection in SHIP-deficient B cells

The strength of the Ag receptor signal influences development and negative selection of B cells, and it might also affect B-cell survival and selection in the GC. Here, we have used mice with B-cell-specific deletion of the 5'-inositol phosphatase SHIP as a model to study affinity selection in cells that are hyperresponsive to Ag and cytokine receptor stimulation. In the absence of SHIP, B cells have lower thresholds for Ag- and interferon (IFN)-induced activation, resulting in augmented negative selection in the BM and enhanced B-cell maturation in the periphery. Despite a tendency to spontaneously downregulate surface IgM expression, SHIP deficiency does not alter anergy induction in response to soluble hen-egg lysozyme Ag in the MDA4 transgenic model. SHIP-deficient B cells spontaneously produce isotype-switched antibodies; however, they are poor responders in immunization and infection models. While SHIP-deficient B cells form GCs and undergo mutation, they are not properly selected for high-affinity antibodies. These results illustrate the importance of negative regulation of B-cell responses, as lower thresholds for B-cell activation promote survival of low affinity and deleterious receptors to the detriment of optimal Ab affinity maturation.

An IL15-dependent novel immune cell subset with multiple functionalities affecting the onset and severity of autoimmune disease (171.36)

Interferon-producing killer dendritic cells (IKDC) are a recently discovered innate cell subset that shares morphological and functional characteristics of NK and DC cells. The aim of this study is to investigate the role of IKDCs in terms of initiating autoimmune disease. We found that these cells are expanded in mice with multiple copies of the TLR7 gene and that the number of these cells correlates with disease activity. Expansion of this population is due to their cell intrinsic sensitivity to TLR7 stimulation. IKDCs are dependent of IL15, produce high levels of IFN type I and type II after stimulation with a TLR7 agonist, are capable of MHC class II antigen presentation, and can cross-present antigen to CD8 cells. Adoptive transfer of IKDC to wild type mice causes activation of naïve T cells, expansion of inflammatory monocyte populations and IFN-dependent CD8 activation. IKDC adoptive transfer also induces elevated inflammatory cytokine and IgG levels in the serum. We found that IFN type I and CD40/CD40L interactions are essential for the inflammatory effect of these cells. Taken together these results uncover a potential role for this cell populaiton in the development of autoimmune pathologies.

Altered CD4+ T cell differentiation with preferential expansion of Th1 cells in TLR7-driven autoimmunity (171.45)

TLR7 is a single-stranded RNA-recognizing innate immune receptor with roles in anti-viral immunity and systemic lupus erythematosus (SLE) in humans and SLE-like autoimmunity in mice. TLR7 gene duplication drives inflammation and autoimmunity in the BXSB mouse model and other Y autoimmune accelerator (Yaa)-derived models of murine lupus. Additionally, TLR7 SNPs associate with SLE in Eastern Asian populations. In this study, we investigated effects of TLR7 overexpression on CD4+ T cell subsets. In unmanipulated, 5-6 month old TLR7 BAC transgenic mice, we observed amplified activated:naïve T cell ratios and preferential expansion of the Th1 subset compared to wild type controls. We also evaluated the phenotype of TCR transgenic T cells specific for the RNA-binding autoantigen, human La, following adoptive transfer into TLR7 BAC transgenic mice. These human La-specific T cells demonstrated enhanced differentiation to Th1 and PSGL1lowCXCR4+ extrafollicular helper phenotypes after recovery from TLR7-overexpressing human La transgenic mice compared to wild type human La transgenic controls seven days after transfer. Moreover, TLR7 overexpression in recipient mice resulted in significantly reduced expansion of the CD4+ Foxp3+ phenotype among transferred, human La-specific cells. These data indicate that TLR7 overexpression alters CD4+ T cell populations in a manner that potentially contributes to autoinflammatory disease in these animals.

Ifih1 gene dose effect reveals MDA5-mediated chronic type I IFN gene signature, viral resistance, and accelerated autoimmunity

Type I IFNs (IFN-I) are normally produced during antiviral responses, yet high levels of chronic IFN-I expression correlate with autoimmune disease. A variety of viral sensors generate IFN-I in their response, but other than TLRs, it is not fully known which pathways are directly involved in the development of spontaneous immune pathologies. To further explore the link between IFN-I induced by viral pathways and autoimmunity, we generated a new transgenic mouse line containing multiple copies of Ifih1, a gene encoding the cytoplasmic dsRNA sensor MDA5 with proven linkage to diabetes and lupus. We show that MDA5 overexpression led to a chronic IFN-I state characterized by resistance to a lethal viral infection through rapid clearance of virus in the absence of a CD8(+) or Ab response. Spontaneous MDA5 activation was not sufficient to initiate autoimmune or inflammatory pathology by itself, even though every immune cell population had signs of IFN activation. When combined with the lupus-susceptible background of the FcγR2B deficiency, MDA5 overexpression did accelerate the production of switched autoantibodies, the incidence of glomerulonephritis, and early lethality. Thus, MDA5 transgenic mice provide evidence that chronic elevated levels of IFN-I are not sufficient to initiate autoimmunity or inflammation although they might exacerbate an ongoing autoimmune pathology.

A balance of Bruton's tyrosine kinase and SHIP activation regulates B cell receptor cluster formation by controlling actin remodeling

The activation of the BCR, which initiates B cell activation, is triggered by Ag-induced self-aggregation and clustering of receptors at the cell surface. Although Ag-induced actin reorganization is known to be involved in BCR clustering in response to membrane-associated Ag, the underlying mechanism that links actin reorganization to BCR activation remains unknown. In this study, we show that both the stimulatory Bruton's tyrosine kinase (Btk) and the inhibitory SHIP-1 are required for efficient BCR self-aggregation. In Btk-deficient B cells, the magnitude of BCR aggregation into clusters and B cell spreading in response to an Ag-tethered lipid bilayer is drastically reduced, compared with BCR aggregation observed in wild-type B cells. In SHIP-1(-/-) B cells, although surface BCRs aggregate into microclusters, the centripetal movement and growth of BCR clusters are inhibited, and B cell spreading is increased. The persistent BCR microclusters in SHIP-1(-/-) B cells exhibit higher levels of signaling than merged BCR clusters. In contrast to the inhibition of actin remodeling in Btk-deficient B cells, actin polymerization, F-actin accumulation, and Wiskott-Aldrich symptom protein phosphorylation are enhanced in SHIP-1(-/-) B cells in a Btk-dependent manner. Thus, a balance between positive and negative signaling regulates the spatiotemporal organization of the BCR at the cell surface by controlling actin remodeling, which potentially regulates the signal transduction of the BCR. This study suggests a novel feedback loop between BCR signaling and the actin cytoskeleton.

VSV infection ameliorates autoimmune disease in FcγR2B deficient mice (101.14)

We have investigated whether infection by pathogens affects the development of autoimmune diseases such as lupus. We tested the effect of infection with vesicular stomatitis virus (VSV) on two mouse strains that spontaneously develop lupus disease. Infection of VSV in lupus prone FcγR2B-/- (R2) mice significantly reduced autoantibody titers and inflammatory cytokines and chemokines in serum, reduced glomerulonephritis, and improved survival. In contrast, VSV infection in R2yaa mice, which develop a more aggressive lupus disease, showed slightly reduced auto-antibody titers in the serum without any major changes in serum cytokines and chemokines, kidney glomreulonephritis, or survival. Characterization of immune cell phenotypes in VSV infected R2 mice showed that B cell development in the bone marrow was not affected whereas germinal center, plasma, and IgG producing mature B cell numbers were reduced. Additionally, VSV infected R2 mice had lower number of follicular helper T cells and CD11c+ cells in the spleen. Compared to uninfected mice, microarray analysis of naïve resting B cells from VSV infected R2 splenocytes showed up-regulation of several candidate genes including a non receptor type protein tyrosine phosphatase, PTPN22 that has been shown to be associated with Lupus and other autoimmune diseases. Studies of the functional implications of Ptpn22 overexpression in VSV-infected R2 B cells are in progress.

Transgenic expression of MDA5 enhances interferon responses, CD8 activation, and viral clearance (110.19)

MDA5 is a pattern recognition receptor responsible for detecting double stranded viral RNA in the cytoplasm. Ligation of MDA5 leads to the induction of inflammatory cytokines and type one interferons (IFN-I) that help coordinate the adaptive and innate immune response against the virus. Here, we describe the phenotype of mice overexpressing MDA5 under its endogenous promoter. MDA5 transgenic (MDA5 Tg) mice have normal numbers of B and T cells, yet expanded numbers of CD11b+ cells expressing Ly6C. Splenocytes isolated from MDA5 Tg display an interferon gene expression signature. MDA5 Tg CD8+ T cells have increased surface expression of CD44, CD69, Ly6C and Ly6A/E, indicative of an activated phenotype. In vitro, CD8+ T cells from MDA5 tg hyperrespond to stimulation. Surprisingly, MDA5 tg mice fail to mount a CD8+ T cell-driven antigen-specific immune response against Vesicular stomatitis virus (VSV). MDA5 tg mice also lacked VSV neutralizing antibodies 16 days after infection with the virus. Although MDA5 tg mice failed to mount a full immune response against the virus, they were resistant to a lethal dose of VSV. This result suggests that increased viral resistance of MDA5 Tg is independent of antibody-neutralization and CD8+ T cell-mediated clearance, and might be due to high expression levels of interferon inducible inhibitors of virus replication. MDA5 tg mice could serve as a model for diseases involving type one interferon and CD8+ T cells, such as Type One Diabetes.

Role of interferon-producing killer dendritic cells in the development of autoimmune disease (44.14)

Interferon-producing killer dendritic cells (IKDCs) share functional characteristics with NK cells and DCs. We investigated their role in the autoimmune disease developed by transgenic mice that overexpress TLR7 (TLR7tg). We determined that a cell population resembling IKDCs expands in TLR7tg mice through their intrinsic sensitivity to TLR7 stimulation. We confirmed that they are bona fide NK cells by their ability to kill cells lacking MHC I molecules in vitro. These cells were also able to present antigen to naïve T cells in in vitro assays. Adoptive transfer of IKDCs isolated from TLR7tg mice into wild type mice induced priming and activation of naïve T cells. In vitro stimulation with TLR7 agonists of IKDCs derived from TLR7tg resulted in the production of TNFa, MCP-1, IFNa and high levels of IL-10. We also tested the requirement of cytokines that are essential for NK cell development. We found that the expansion of IKDCs in TLR7tg mice was IL15 dependent but IL18 independent. We observed that lack of IL15 reduced many pro-inflammatory subsets (Ly6C+monocytes, granulocytes, DCs and memory T cells) and delayed the development of glomerulonephritis in TLR7tg mice. These results reveal expansion of IKDCs in autoimmune inflammatory conditions and suggest a dual role for these cells in both the priming of autoreactive T cells and the release of inflammatory cytokines.

Toll-like receptor3 overexpression alters responses to toll-like receptor7 ligand (111.6)

Macrophages are key components of the inflammatory response. PolyIC induces type I IFN and inflammatory responses through TLR3 or MDA5 pathway, depending on the activating conditions and cell types. In our hands, bone marrow-derived macrophages (BMM) in vitro preferentially engage TLR3 in response to stimulation with naked poly IC. In contrast, the same macrophages activate TLR3-independent pathways in response to Fugene-complexed poly IC.These results suggest that lipid-complexed poly IC is more likely to induce inflammatory cytoplasmic pathways. To further investigate the role of TLR3 in macrophage activation, we have generated TLR3-overexpressing transgenic mice (TLR3 Tg). TLR3 Tg mice contain 20-30 copies of a BAC clone which spans the entire mouse tlr3 gene. As a consequence, TLR3 mRNA expression is greatly enhanced in BMM and splenoctes of TLR3 Tg mice. These mice had normal life span and no obvious changes in immunological characteristics or spontaneous pathology. When we stimulated TLR3 Tg BMM with naked poly IC, we detected a small increase in their hyperresponsiveness to poly IC compared to WT cells. Interestingly, TLR3 Tg BMM greatly enhanced the synergistic effect of TLR7 agonist pretreatment with naked poly IC in the inflammatory cytokine secretion, but did not enhance the TLR9 agonist pretreatment. In the future, we will further investigate the mechanisms involved in these effects and explore in vivo consequences of TLR receptor cross-regulation.

Coordinate suppression of B cell lymphoma by PTEN and SHIP phosphatases

Mice lacking both PTEN and SHIP phosphatases develop spontaneous B cell lymphoma.

The inositol phosphatases phosphatase and tensin homologue (PTEN) and Src homology 2 domain–containing inositol phosphatase (SHIP) negatively regulate phosphatidylinositol-3-kinase (PI3K)–mediated growth, survival, and proliferation of hematopoietic cells. Although deletion of PTEN in mouse T cells results in lethal T cell lymphomas, we find that animals lacking PTEN or SHIP in B cells show no evidence of malignancy. However, concomitant deletion of PTEN and SHIP (bPTEN/SHIP^−/−) results in spontaneous and lethal mature B cell neoplasms consistent with marginal zone lymphoma or, less frequently, follicular or centroblastic lymphoma. bPTEN/SHIP^−/− B cells exhibit enhanced survival and express more MCL1 and less Bim. These cells also express low amounts of p27^kip1 and high amounts of cyclin D3 and thus appear poised to undergo proliferative expansion. Unlike normal B cells, bPTEN/SHIP^−/− B cells proliferate to the prosurvival factor B cell activating factor (BAFF). Interestingly, although BAFF availability may promote lymphoma progression, we demonstrate that BAFF is not required for the expansion of transferred bPTEN/SHIP^−/− B cells. This study reveals that PTEN and SHIP act cooperatively to suppress B cell lymphoma and provides the first direct evidence that SHIP is a tumor suppressor. As such, assessment of both PTEN and SHIP function are relevant to understanding the etiology of human B cell malignancies that exhibit augmented activation of the PI3K pathway.

A BALB/c locus on chromosome 12 confers resistance to lupus in FcγR2-/- mice. (93.23)

FcγR2B-deficient (R2-/-) mice develop autoantibodies and glomerulonephritis with a pathology resembling human lupus when on the C57Bl/6 background. The same mutation on the BALB/c background does not lead to spontaneous disease, suggesting differences in lupus susceptibility between the BALB/c and B6 strains. An F2 genetic analysis from a B6/BALB cross identified region from the B6 chromosome 12 with positive linkage for autoantibodies. We have generated a congenic strain (B6.R2-/-sbb2) that contains the suppressor allele from the BALB/c centromeric region of chromosome 12 in an otherwise B6.R2-/- background. We have observed that the presence of sbb2 renders B6.R2-/- mice resistant to lupus disease by suppressing all antibody autoreactivity and spontaneous immune cell activation. Mixed bone marrow reconstitution experiments indicated that the sbb2 resistant allele is most likely T cell intrinsic. The sbb2 congenic interval contains several candidate genes that are currently being investigated. We generated transgenic lines containing BAC DNA insertions spanning the sbb2 interval. The new BAC transgenic strains were tested in the induced model of lupus by pristane administration. Newly generated BAC transgenic strains were also bred to B6.R2-/- to test for suppression of lupus in spontaneous disease. The goal of our experiments is to identify a new lupus susceptibility gene within the sbb2 interval that is able to suppress lupus disease by altering T cell function.