Antigen presentation, but not antibody secretion, by B cells drives CNS autoimmunity induced by immunization with human MOG.
Whether B cells serve as antigen-presenting cells (APCs) for activation of pathogenic T cells in the multiple sclerosis model experimental autoimmune encephalomyelitis (EAE) is unclear. To evaluate their role as APCs, we engineered mice selectively deficient in MHC II on B cells (B–MHC II−/−), and to distinguish this function from antibody production, we created transgenic (Tg) mice that express the myelin oligodendrocyte glycoprotein (MOG)–specific B cell receptor (BCR; IgHMOG-mem) but cannot secrete antibodies. B–MHC II−/− mice were resistant to EAE induced by recombinant human MOG (rhMOG), a T cell– and B cell–dependent autoantigen, and exhibited diminished Th1 and Th17 responses, suggesting a role for B cell APC function. In comparison, selective B cell IL-6 deficiency reduced EAE susceptibility and Th17 responses alone. Administration of MOG-specific antibodies only partially restored EAE susceptibility in B–MHC II−/− mice. In the absence of antibodies, IgHMOG-mem mice, but not mice expressing a BCR of irrelevant specificity, were fully susceptible to acute rhMOG-induced EAE, also demonstrating the importance of BCR specificity. Spontaneous opticospinal EAE and meningeal follicle–like structures were observed in IgHMOG-mem mice crossed with MOG-specific TCR Tg mice. Thus, B cells provide a critical cellular function in pathogenesis of central nervous system autoimmunity independent of their humoral involvement, findings which may be relevant to B cell–targeted therapies.
The transcription factor IRF4 limits the retention of B cells in the marginal zone by inhibiting NOTCH2 signaling.
The transcription factor interferon regulatory factor-4 (IRF4) is expressed in B cells at most developmental stages. In antigen-activated B cells, IRF4 controls germinal center formation, class-switch recombination, and the generation of plasma cells. Here we describe a novel function for IRF4 in the homeostasis of mature B cells. Inducible deletion of irf4 specifically in B cells in vivo led to the aberrant accumulation of irf4-deleted follicular B cells in the marginal zone (MZ) area. IRF4-deficient B cells showed elevated protein expression and activation of NOTCH2, a transmembrane receptor and transcriptional regulator known to be required for MZ B cell development. Administration of a NOTCH2-inhibitory antibody abolished nuclear translocation of NOTCH2 in B cells within 12 h and caused a rapid and progressive disintegration of the MZ that was virtually complete 48 h after injection. The disappearance of the MZ was accompanied by a transient increase of MZ-like B cells in the blood rather than increased B cell apoptosis, demonstrating that continued NOTCH2 activation is critical for the retention of B cells in the MZ. Our results suggest that IRF4 controls the positioning of mature B cells in the lymphoid microenvironments by regulating NOTCH2 expression. These findings may have implications for the understanding of B cell malignancies with dysregulated IRF4 and NOTCH2 activity.
TLR9 suppresses TLR7-driven pathogenesis in the MRL.Faslpr murine model of systemic lupus erythematosus, but the mechanisms by which TLR7 promotes and TLR9 prevents disease in this and other lupus models remain unclear. Type I interferons have also been implicated in the pathogenesis of lupus both in patients and in several murine models of disease, but their role in MRL.Faslpr mice is controversial. Using MRL.Faslpr mice genetically deficient in a subunit of the receptor for type I interferon, Ifnar1, we show that type I interferons contribute significantly to renal disease in this model. Ifnar1 had no effect on anti-nucleosome or anti-Sm autoantibody titers, but instead regulated anti-cytoplasmic and anti-RNA specificities. Moreover, Ifnar1 deficiency prevented the exacerbation of clinical disease observed in Tlr9-deficient animals in this lupus model. Thus, type I interferon signaling is an important mediator of lupus pathogenesis and anti-RNA antibody production that is dysregulated in the absence of Tlr9.
autoimmunity; systemic lupus erythematosus; TLR9; IFN–I
CD73 catalyzes the conversion of extracellular nucleosides to adenosine, modulating inflammatory and T cell responses. Elevated expression of CD73 marks subpopulations of murine memory B cells (MBC), but its role in memory development or function is unknown. Here, we demonstrate that CD73 is progressively upregulated on germinal center (GC) B cells following immunization, is expressed at even higher levels among T follicular helper cells, but is absent among plasma cells (PC) and plasmablasts (PB). We analyzed the T-dependent B cell response in CD73 knockout mice (CD73KO). During the early response, CD73KO and wild type (WT) mice formed GCs, MBCs and splenic PBs and PCs similarly, and MBCs functioned similarly in the early secondary response. Late in the primary response, however, bone marrow (BM) PCs were markedly decreased in CD73KO animals. Tracking this phenotype, we found that CD73 expression was required on BM-derived cells for optimal BM PC responses. However, deletion of CD73 from either B or T lymphocytes alone did not recapitulate the phenotype. This suggests that CD73 expression is sufficient on either cell type, consistent with its function as an ectoenzyme. Together, these findings suggest that CD73-dependent adenosine signaling is prominent in the mature GC and required for establishment of the long-lived PC compartment, thus identifying a novel role for CD73 in humoral immunity.
Detection of self nucleic acids by Toll-like receptors (TLR) preciptates autoimmune diseases, including systemic lupus erythematosus (SLE). It remains unknown how TLR signals in specific cell types contribute to distinct manifestations of SLE. Here, we demonstrate that formation of anti-nuclear antibodies in MRL.Faslpr mice entirely depends on the TLR signaling adaptor MyD88 in B cells. Further, MyD88 deficiency in B cells ameliorated nephritis, including antibody-independent interstitial T cell infiltrates, suggesting that nucleic acid-specific B cells activate nephrotoxic T cells. Surprisingly, MyD88 deletion in dendritic cells (DCs) did not affect nephritis, despite the importance of DCs in renal inflammation. In contrast, MyD88 in DCs was critical for dermatitis, revealing a separate pathogenetic mechanism. DC-expressed MyD88 promoted interferon-α production by plasmacytoid DCs, which was associated with Death domain-associated protein 6 upregulation and B lymphopenia. Our findings thus reveal unique immunopathological consequences of MyD88 signaling in B cells and DCs in lupus.
B cells are critical in the initiation and maintenance of lupus. Autoreactive B cells clonally expand, isotype switch and mutate—properties associated with memory B cells (MBC), which are typically generated via germinal centers (GCs). The development and functions of autoreactive MBC in lupus are poorly understood. Moreover, mounting evidence implicates the extrafollicular (EF) response in the generation of switched and mutated autoantibodies that are driven by BCR and TLR co-recognition, raising the question of whether MBC are generated in this context. Here we investigated autoreactive MBC generation associated with this type of response. We transferred B cells from AM14 site directed BCR transgenic mice into non-transgenic normal recipients and elicited an EF response with anti-chromatin Ab, as in prior studies. By following the fate of the stimulated cells at late time points we found that AM14 B cells persisted at increased frequency for up to 7 weeks. Furthermore, these cells had divided in response to Ag, but were subsequently quiescent, with a subset expressing the memory marker CD73. These cells engendered rapid, isotype switched secondary plamablast responses upon restimulation. Both memory and rapid secondary responses required T cell help to develop, emphasizing the need for T-B collaboration for long-term self-reactivity. Thus, using this model system, we show that the EF response generated persistent and functional MBC that share some but not all of the characteristics of traditional MBC. Such cells could play a role in chronic or flaring autoimmune disease.
Nucleic acid reactive B cells frequently arise in the bone marrow but are tolerized by mechanisms including receptor editing, functional anergy, and/or deletion. TLR9, a sensor of endosomal dsDNA, both promotes and regulates systemic autoimmunity in vivo, but the precise nature of its apparently contradictory roles in autoimmunity remained unclear. Here, using the 3H9 anti-DNA BCR transgene in the autoimmune-prone MRL.Faslpr mouse model of systemic lupus erythematosus, we identify the stages at which TLR9 contributes to establishing and breaking B cell tolerance. Although TLR9 is dispensable for light chain editing during B cell development in the bone marrow, TLR9 limits anti-DNA B cell lifespan in the periphery and is thus tolerogenic. In the absence of TLR9, anti-DNA B cells have much longer lifespans and accumulate in the follicle, neither activated nor deleted. These cells retain some characteristics of anergic cells, in that they have elevated basal BCR signaling but impaired induced responses and downregulate their cell surface BCR expression. In contrast, while TLR9-intact anergic B cells accumulate near the T/B border, TLR9-deficient anti-DNA B cells are somewhat more dispersed throughout the follicle. Nonetheless, in older autoimmune-prone animals, TLR9 expression specifically within the B cell compartment is required for spontaneous peripheral activation of anti-DNA B cells and their differentiation into AFCs via an extrafollicular pathway. Thus, TLR9 has paradoxical roles in regulating anti-DNA B cells: it helps purge the peripheral repertoire of autoreactive cells yet is also required for their activation.
Typhoid fever and non-typhoidal bacteremia caused by Salmonella remain critical human health problems. B cells are required for protective immunity to Salmonella but the mechanism of protection remains unclear. Here, we immunized WildType, B cell deficient, antibody-deficient and class-switched antibody-deficient mice with attenuated Salmonella and examined protection against secondary infection. As expected, WildType mice were protected and B cell deficient mice succumbed to secondary infection. Interestingly, mice with B cells but lacking secreted antibody or class-switched antibody had little deficiency in resistance to Salmonella infection. The susceptibility of B cell deficient mice correlated with marked reductions in CD4 T cell IFN-γ production after secondary infection. Together, these data suggest that the primary role of B cells in acquired immunity to Salmonella is via the development of protective T cell immunity.
The AM14 rheumatoid factor (RF) transgenic (Tg) mouse has been valuable for studying how self-reactive B cells are regulated beyond central tolerance, because they remain ignorant in normal mice. AM14 B cell activation can be studied on autoimmune-prone strains or by inducing activation with IgG2a anti-chromatin antibodies. Despite the utility of conventional Ig-Tg mice, site-directed Ig Tg (sd-Tg) mice provide a more physiological model for B cell responses, allowing class switch and somatic hypermutation. We report here the creation of an AM14 sd-Tg mouse and describe its phenotype on both normal and autoimmune-prone backgrounds. AM14 sd-Tg B cells develop normally but remain unactivated on the BALB/c background, even after significant aging. In contrast, on the autoimmune prone strain MRL/lpr, AM14 sd-Tg B cells become activated and secrete large amounts of IgG RF antibody into the serum. Class-switched antibody forming cells were found in the spleen and bone marrow. IgG RF plasmablasts were also observed in extrafollicular clusters in the spleens of aged AM14 sd-Tg MRL/lpr mice. Class switch and antibody secretion were observed additionally in AM14 sd-Tg BALB/c B cells activated in vivo using IgG2a anti-chromatin antibodies. Development of IgG autoantibodies is a hallmark of severe autoimmunity, and is related to pathogenesis. Using the AM14 sd-Tg, we now show that switched autoantibody-forming cells develop robustly outside germinal centers, further confirming the extrafollicular expression of AID. This model will allow more physiological studies of B cell biology in the future, including memory responses marked by class switch.
plasmablast; isotype switch; lupus; extrafollicular response
Aberrant targeting of the enzyme Activation Induced Cytidine Deaminase (AID) results in the accumulation of somatic mutations in approximately 25% of expressed genes in germinal center B cells. Observations in Ung−/− Msh2−/− mice suggest that many other genes efficiently repair AID-induced lesions, so that up to 45% of genes may actually be targeted by AID. It is important to understand the mechanisms that recruit AID to certain genes, as this mis-targeting represents an important risk for genome instability. We hypothesize that several mechanisms will combine to target AID to each locus. In order to resolve which mechanisms affect AID targeting, we analyze 7.3Mb of sequence data, along with the regulatory context, from 83 genes in Ung−/− Msh2−/− mice to identify common properties of AID targets. This analysis identifies the involvement of three transcription factor binding sites (E-box motifs, along with YY1 and C/EBP-beta binding sites) that may work together to recruit AID. Based on previous knowledge and these newly discovered features, a classification tree model was built to predict genome-wide AID targeting. Using this predictive model we were able to identify a set of 101 high-interest genes that are likely targets of AID.
Germinal centers (GCs) generate memory B and plasma cells, essential for long-lived humoral immunity. GC B cells with high affinity B cell receptors (BCRs) are selectively expanded. To enable this selection, BCRs of such cells are thought to signal differently from those with lower affinity. We show that, surprisingly, most proliferating GC B cells did not demonstrate active BCR signaling. Rather, spontaneous and induced signaling was limited by increased phosphatase activity. Accordingly, both SHP-1 and SHIP-1 were hyperphosphorylated in GC cells and remained colocalized with BCRs after ligation. Furthermore, SHP-1 was required for GC maintenance. Intriguingly, GC B cells in the cell cycle G2 period regained responsiveness to BCR stimulation. These data have implications for how higher affinity B cells are selected in the GC.
Polyaromatic hydrocarbons (PAHs) are prevalent, potent carcinogens, and 7,12-dimethylbenz[a]anthracene (DMBA) is a model PAH widely used to study tumorigenesis. Mice lacking Langerhans cells (LCs), a signatory epidermal dendritic cell (DC), are protected from cutaneous chemical carcinogenesis, independent of T cell immunity. Investigation of the underlying mechanism revealed that LC-deficient skin was relatively resistant to DMBA-induced DNA damage. LCs efficiently metabolized DMBA to DMBA-trans-3,4-diol, an intermediate proximal to oncogenic Hras mutation, and DMBA-treated LC-deficient skin contained significantly fewer Hras mutations. Moreover, DMBA-trans-3,4-diol application bypassed tumor resistance in LC-deficient mice. Additionally, the genotoxic impact of DMBA on human keratinocytes was significantly increased by prior incubation with human-derived LC. Thus, tissue-associated DC can enhance chemical carcinogenesis via PAH metabolism, highlighting the complex relation between immune cells and carcinogenesis.
The mechanism of skin allograft rejection has been thought to require presentation of graft antigen by resident epidermal Langerhans cells (LCs). We have previously engineered mice that have a selective and constitutive absence of epidermal LCs. By using donor skin from these LC-deficient mice, we show that LCs are not required for rejection of major (FVB→B6) or minor (H-Y, male→female on B6 background) antigen-mismatched skin grafts. On the FVB background, where H-Y mismatched grafts are normally maintained indefinitely, grafts lacking LCs are efficiently rejected. Thus, LCs in the donor graft are required for long-term skin engraftment, which supports a regulatory role for LCs in skin graft acceptance.
Germinal center (GC) B cells and T follicular helper (TFH) cells interact in the production of high-affinity long-lived plasma cells (PCs) and memory B cells, though the mechanisms regulating the formation of these long-lived populations remain unclear. Because CD80 is one of the few markers shared by human and murine memory B cells, we investigated its role in the development of GCs, memory cells and PCs. In CD80-deficient mice, fewer long-lived PCs were generated upon immunization, compared to B6 controls. In concert, the absence of CD80 resulted in an increase in apoptotic GC B cells during the contraction phase of the GC. CD80−/− mice had fewer TFH compared to B6, and residual TFH cells failed to mature, with decreased ICOS and PD-1 expression and decreased synthesis of IL-21 mRNA. Mixed bone marrow chimeras demonstrated a B cell-intrinsic requirement for CD80 expression for normal TFH and PC development. Therefore, B cell expression of CD80 plays a critical role in regulating B-T interactions in both early and late GC responses. This, in turn, results in impaired ability to produce long-lived PCs. These data provide new insights into the development of GCs and AFCs and the functions of CD80 in humoral immunity.
To simulate transient B cell activation that is the likely initiator of T-dependent responses, we examined the molecular and functional consequences of a single-round of immunoglobulin M (IgM) signaling. This form of activation triggered early cytosolic signaling and the transcription factor NF-κB activation indistinguishably from conventional continuous IgM cross-linking, but did not induce G1 progression. However, single-round IgM signaling changed the expression of chemokine and chemokine receptor genes implicated in initiating T-dependent responses, as well as accentuated responsiveness to CD40 signaling. Several features of single-round IgM signaling in vitro were recapitulated in B cells after short-term exposure to antigen in vivo. We propose that transient BCR signals prime B cells to receive T cell help by increasing the probability of B-T encounter and creating a cellular environment that is hyper-responsive to CD40 signaling.
B cells contribute to the pathogenesis of chronic autoimmune disorders like systemic lupus erythematosus (SLE) via multiple effector functions. However, B cells are also implicated in regulating SLE and other autoimmune syndromes via release of IL-10. B cells secreting IL-10 have been termed “Breg” and have been proposed as a separate subset of cells, a concept that remains controversial. The balance between pro- and anti-inflammatory effects could determine the success of B cell targeted therapies for autoimmune disorders and it is therefore pivotal to understand the significance of B cell-secreted IL-10 in spontaneous autoimmunity. By lineage specific deletion of Il10 from B cells we demonstrate that B cell-derived IL-10 is ineffective in suppressing the spontaneous activation of self-reactive B and T cells during lupus. Correspondingly, severity of organ disease and survival rates in mice harboring Il10 deficient B cells are unaltered. Genetic marking of cells that transcribe Il10 illustrates that the pool of IL-10 competent cells is dominated by CD4 T cells and macrophages. IL-10 competent cells of the B lineage are rare in vivo and among them short-lived plasmablasts have the highest frequency, suggesting an activation rather than lineage-driven phenotype. Putative Breg phenotypic subsets such as CD1dhiCD5+ and CD21hiCD23hi B cells are not enriched in Il10 transcription. These genetic studies demonstrate that in a spontaneous model of murine lupus, IL-10 dependent B cell regulation does not restrain disease and thus the pathogenic effects of B cells are not detectably counterbalanced by their IL-10 dependent regulatory functions.
A dominant type of spontaneous autoreactive B cell activation in murine lupus is the extrafollicular generation of plasmablasts. The factors governing such activation have been difficult to identify due to the stochastic onset and chronic nature of the response. Thus, the ability to induce a similar autoreactive B cell response with a known autoantigen in vivo would be a powerful tool in deciphering how autoimmune responses are initiated. We report here the establishment and characterization of a system to initiate autoreactive extrafollicular B cell responses that closely mirror the spontaneous response using IgG anti-chromatin Abs. We demonstrate that exogenously administered anti-chromatin Ab, presumably by forming immune complexes (ICs) with released nuclear material, drives activation of RF B cells in AM14 Tg mice. Anti-chromatin elicits autoreactive B cell activation and development into AFCs at the T-zone/red pulp border. Plasmablast generation occurs equally in BALB/c, MRL/+ and MRL/lpr mice, indicating that an autoimmune-prone genetic background is not required for the induced response. Importantly, infused IgG anti-chromatin induces somatic hypermutation (SHM) in the absence of a GC response, thus proving the extrafollicular SHM pathway. This system provides a window on the initiation of an autoantibody response and reveals authentic initiators of it.
B cells; autoantibodies; systemic lupus erythematosus
Graft-vs.-host disease (GVHD) caused by donor T cells attacking recipient tissues is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (alloSCT). Studies have shown that effector memory T cells (TEM) do not cause GVHD but are capable of immune functions post-transplant, including graft-vs.-leukemia (GVL) effects, but the reasons for this are unclear. In mice, the TEM pool may have a less-diverse T cell receptor (TCR) repertoire than TN with fewer alloreactive clones. We therefore tested whether enhancing the alloreactivity of TEM would restore their ability to cause GVHD. In an MHC-matched system, alloreactive TEM were created by transferring GVHD effector cells into syngeneic recipients and allowing conversion to TEM. Upon retransfer to freshly transplanted recipients, these cells caused only mild GVHD. Similarly, in an MHC-mismatched system, TEM with a proven increased precursor frequency of alloreactive clones only caused limited GVHD. Nonetheless these same cells mounted strong in vitro alloresponses and caused rapid skin graft rejection. TEM created from CD4 cells that had undergone lymphopenia-induced proliferation also caused only mild GVHD. Our findings establish that conversion to TEM significantly reduces GVHD potency, even in cells with a substantially enhanced alloreactive repertoire.
B cells play important roles in autoimmune diseases ranging from multiple sclerosis to rheumatoid arthritis. B cells have long been considered central players in systemic lupus erythematosus. However, anti-CD20 mediated B cell depletion was not effective in two clinical lupus studies, while anti-BLyS, which inhibits B cell survival, was effective. Others and we previously found that anti-CD20 based depletion was surprisingly ineffective in tissues of lupus-prone mice, but that persistent high doses eventually led to depletion and ameliorated lupus. Lupus patients might also have incomplete depletion, as suggested in several studies, and which could have led to therapeutic failure. Here we investigated the mechanism of resistance to Ab-mediated cellular depletion in murine lupus. B cells from lupus-prone mice were easily depleted when transferred into normal environments or in lupus-prone mice that lacked serum Ig. Serum from lupus-prone mice transferred depletion resistance, with the active component being IgG. Because depletion is FcγR-dependent, we assayed macrophages and neutrophils exposed to lupus mouse serum, showing they are impaired in IgG-mediated phagocytosis. We conclude that depletion resistance is an acquired, reversible phagocytic defect depending on exposure to lupus serum IgG. These results have implications for optimizing and monitoring cellular depletion therapy.
Synthetic oligonucleotides containing CpG motifs (CpG ODNs) have been shown to induce proliferation, differentiation and cytokine production in B cells, macrophages and DCs through a TLR9-dependent mechanism. A class (CpG-A) and B class (CpG-B) ODNs display distinct physical properties. CpG-A, but not CpG-B, can multimerize to form exceedingly large lattices. CpG-A cannot effectively activate B cells but does induce pDCs to produce high levels of IFNα, while CpG-B is a potent B cell mitogen. Here we report that CpG-A is internalized by B cells, and CpG-A and CpG-B accumulate to distinct intracellular compartments. When present in the form of an immune complex (CpG-A IC), CpG-A is taken up more efficiently by AM14 IgG2a-specific B cells, and elicits a robust TLR9-dependent B cell proliferative response. B cells proliferating comparably and in a TLR9-dependent fashion in response to CpG-A IC and CpG-B exhibited distinct cytokine profiles. CpG-A IC induced enhanced production of RANTES and markedly reduced levels of IL-6 when compared to CpG-B. We also found that engagement of the AM14 BCR by a protein IC, which cannot by itself induce proliferation, promoted TLR9-dependent but BCR-independent proliferation by bystander CpG-A or fragments of mammalian dsDNA. These data identify direct and indirect mechanisms by which BCR engagement facilitates access of exogenous ligands to TLR9-associated compartments and subsequent B cell activation.
Type I IFNs play an important, yet poorly characterized, role in systemic lupus erythematosus. To better understand the interplay between type I IFNs and the activation of autoreactive B cells, we evaluated the effect of type I IFN receptor (IFNAR) deficiency in murine B cell responses to common TLR ligands. In comparison to wild-type B cells, TLR7-stimulated IFNAR−/− B cells proliferated significantly less well and did not up-regulate costimulatory molecules. By contrast, IFNAR1−/− B cells did not produce cytokines, but did proliferate and up-regulate activation markers in response to other TLR ligands. These defects were not due to a difference in the distribution of B cell populations or a failure to produce a soluble factor other than a type I IFN. Instead, the compromised response pattern reflected the disruption of an IFN-β feedback loop and constitutively low expression of TLR7 in the IFNAR1−/− B cells. These results highlight subtle differences in the IFN dependence of TLR7 responses compared with other TLR-mediated B cell responses.
In humans and non-obese diabetic (NOD) mice, defects in immune tolerance result in the spontaneous development of type-1-diabetes. Recent studies have ascribed a breakdown in tolerance to dysfunction in regulatory T-cells (Tregs) that is secondary to reduced IL-2 production by T-cells having the NOD diabetes susceptibility region insulin-dependent diabetes 3 (Idd3). Here we demonstrate a peripheral tolerance defect in the dendritic cells (DCs) of NOD mice that is independent of Tregs. NOD CD8 T-cells specific for islet antigens fail to undergo deletion in the pancreatic lymph nodes. Deletion was promoted by expression of the protective alleles of both Idd3 (Il2) and Idd5 in DCs. We further identify a second tolerance defect that involves endogenous CD4 T-cell expression of the disease promoting NOD alleles of these genetic regions. Pervasive insulitis can be reduced by expression of the Idd3 and Idd5 protective alleles by either the antigen-presenting cell or lymphocytes.
Autoimmunity; dendritic cells; tolerance; T cells, diabetes
B cells can influence T cell responses by directly presenting antigen or by secreting antibody that binds to antigen to form immunogenic complexes. Conflicting evidence suggests that persisting antigen/antibody complexes propagate long-term T cell memory; yet other data indicate that memory cells can survive without specific antigen or MHC. Here, the roles of B cells and antigen/antibody complexes in T cell responses to lymphocytic choriomeningitis virus (LCMV) infection were investigated using B cell-deficient or B cell-competent mice. Despite normal lymphocyte expansion after acute infection, B cell-deficient mice rapidly lost CD4+ T cell memory – but not CD8+ T cell memory – during the contraction phase. To determine whether antigen/antibody complexes sustain CD4+ T cell memory, T cell responses were followed in B cell-transgenic (mIg-Tg) mice that have B cells but neither LCMV-specific antibody nor LCMV-immune complex deposition. In contrast to B cell-deficient mice, mIg-Tg mice retained functional T-helper cell memory, indicating that B cells selectively preserve CD4+ T cell memory independently of immune-complex formation. An in vivo consequence of losing CD4+ T cell memory was that B cell-deficient mice were unable to resolve chronic virus infection. These data implicate a B cell function other than antibody production that induces long-term protective immunity.
T cells; B cells; Memory; Viral; Antibodies; Cytokines
Ixodes scapularis ticks transmit a number of human pathogens, including the Lyme disease spirochete Borrelia burgdorferi. I. scapularis suppresses host immunity in the skin to promote feeding and systemically skew T-helper (Th)-cell differentiation toward Th2 cells in secondary lymphoid organs. Although components of tick saliva are known to influence Th-cell polarization, the mechanism whereby tick feeding in the skin modulates regional and systemic Th-cell responses is unknown. In this study, the role of the epidermal Langerhans cell (LC) subset of skin dendritic cells in tick-mediated Th1/Th2-cell immunomodulation was assessed. Mice deficient in LCs (Langerin-DTA mice) exhibited enhanced lymph node (LN) concanavalin A (ConA)-induced Th1 responses after tick infestation in comparison to results for uninfested Langerin-DTA or wild-type (WT) mice, whereas effects on Th2-cell production of interleukin 4 were more variable. Nonetheless, the altered T-cell response did not impact tick feeding or refeeding. Gamma interferon production by ConA-stimulated LN cells of both WT and LC-deficient mice was enhanced by as much as fourfold after B. burgdorferi-infected-tick feeding, indicating that immunomodulatory effects of tick saliva were not able to attenuate the Th1 immune responses induced by this pathogen. Taken together, these findings show a requirement for LCs in the tick-mediated attenuation of Th1 responses in regional lymph nodes but not in the spleens of mice and show that the presence of a pathogen can overcome the Th1-inhibitory effects of tick feeding on the host.
Autoreactive B cells are activated by DNA, chromatin, or chromatin-containing immune complexes (ICs)6 through a mechanism dependent on dual engagement of the BCR and TLR9. We examined the contribution of endogenous DNA sequence elements to this process. DNA sequence can determine both recognition by the BCR and by TLR9. DNA fragments containing CpG islands, a natural source of unmethylated CpG dinucleotides, promote the activation of DNA-reactive B cells derived from BCR transgenic mice as well as DNA-reactive B cells present in the normal repertoire. ICs containing these CpG island fragments are potent ligands for AM14 IgG2a reactive B cells. By contrast, ICs containing total mammalian DNA, or DNA fragments lacking immunostimulatory motifs, fail to induce B cell proliferation, indicating that BCR-crosslinking alone is insufficient to activate low affinity autoreactive B cells. Importantly, priming B cells with IFN-α lowers the BCR activation threshold and relaxes the selectivity for CpG-containing DNA. Together, our findings underscore the importance of endogenous CpG-containing DNAs in the TLR9-dependent activation of autoreactive B cells and further identify an important mechanism through which IFN-α can contribute to the pathogenesis of systemic lupus erythematosus (SLE).