B cells drive early T cell autoimmunity in vivo prior to dendritic cell-mediated autoantigen presentation

B cell MHC haplotype affects follicular inclusion, germinal center participation and plasma cell differentiation in a mouse model of lupus

Introduction

MHC class II molecules are essential for appropriate immune responses against pathogens but are also implicated in pathological responses in autoimmune diseases and transplant rejection. Previous studies have shed light on the systemic contributions of MHC haplotypes to the development and severity of autoimmune diseases. In this study, we addressed the B cell intrinsic MHC haplotype impact on follicular inclusion, germinal center (GC) participation and plasma cell (PC) differentiation in the context of systemic lupus erythematosus (SLE).

Methods

We leveraged the 564Igi mouse model which harbors a B cell receptor knock-in from an autoreactive B cell clone recognizing ribonuclear components, including double-stranded DNA (dsDNA). This model recapitulates the central hallmarks of the early stages of SLE. We compared 564Igi heterozygous offspring on either H2b/b, H2b/d, or H2d/d background.

Results

This revealed significantly higher germinal center (GC) B cell levels in the spleens of H2b/b and H2b/d as compared to H2d/d (p<0.0001) mice. In agreement with this, anti-dsDNA-antibody levels were higher in H2b/b and H2b/d than in H2d/d (p<0.0001), with H2b/b also being higher compared to H2b/d (p<0.01). Specifically, these differences held true both for autoantibodies derived from the knock-in clone and from wild-type (WT) derived clones. In mixed chimeras where 564Igi H2b/b, H2b/d and H2d/d cells competed head-to-head in the same environment, we observed a significantly higher inclusion of H2b/b cells in GC and PC compartments relative to their representation in the B cell repertoire, compared to H2b/d and H2d/d cells. Furthermore, in mixed chimeras in which WT H2b/b and WT H2d/d cells competed for inclusion in GCs associated with an epitope spreading process, H2b/b cells participated to a greater extent and contributed more robustly to the PC compartment. Finally, immature WT H2b/b cells had a higher baseline of BCRs with an autoreactive idiotype and were subject to more stringent negative selection at the transitional stage.

Discussion

Taken together, our findings demonstrate that B cell intrinsic MHC haplotype governs their capacity for participation in the autoreactive response at multiple levels: follicular inclusion, GC participation, and PC output. These findings pinpoint B cells as central contributors to precipitation of autoimmunity.

Antigen presentation by B cells enables epitope spreading across an MHC barrier

Circumstantial evidence suggests that B cells may instruct T cells to break tolerance. Here, to test this hypothesis, we used a murine model in which a single B cell clone precipitates an autoreactive response resembling systemic lupus erythematosus (SLE). The initiating clone did not need to enter germinal centers to precipitate epitope spreading. Rather, it localized to extrafollicular splenic bridging channels early in the response. Autoantibody produced by the initiating clone was not sufficient to drive the autoreactive response. Subsequent epitope spreading depended on antigen presentation and was compartmentalized by major histocompatibility complex (MHC). B cells carrying two MHC haplotypes could bridge the MHC barrier between B cells that did not share MHC. Thus, B cells directly relay autoreactivity between two separate compartments of MHC-restricted T cells, leading to inclusion of distinct B cell populations in germinal centers. Our findings demonstrate that B cells initiate and propagate the autoimmune response.

Primary Biliary Cholangitis and Primary Sclerosing Cholangitis: Current Knowledge of Pathogenesis and Therapeutics

Cholangiopathies encompass various biliary diseases affecting the biliary epithelium, resulting in cholestasis, inflammation, fibrosis, and ultimately liver cirrhosis. Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are the most important progressive cholangiopathies in adults. Much research has broadened the scope of disease biology to genetic risk, epigenetic changes, dysregulated mucosal immunity, altered biliary epithelial cell function, and dysbiosis, all of which interact and arise in the context of ill-defined environmental triggers. An in-depth understanding of the molecular pathogenesis of these cholestatic diseases will help clinicians better prevent and treat diseases. In this review, we focus on the main underlying mechanisms of disease initiation and progression, and novel targeted therapeutics beyond currently approved treatments.

T Cell Help in the Autoreactive Germinal Center

The germinal center serves as a site of B cell selection and affinity maturation, critical processes for productive adaptive immunity. In autoimmune disease tolerance is broken in the germinal center reaction, leading to production of autoreactive B cells that may propagate disease. Follicular T cells are crucial regulators of this process, providing signals necessary for B cell survival in the germinal center. Here we review the emerging roles of follicular T cells in the autoreactive germinal center. Recent advances in immunological techniques have allowed study of the gene expression profiles and repertoire of follicular T cells at unprecedented resolution. These studies provide insight into the potential role follicular T cells play in preventing or facilitating germinal center loss of tolerance. Improved understanding of the mechanisms of T cell help in autoreactive germinal centers provides novel therapeutic targets for diseases of germinal center dysfunction.

Profile of T and B lymphocytes in individuals resistant to Schistosoma mansoni infection

The mechanisms involved in the development of resistance to infection/reinfection by Schistosoma mansoni still arouse great interest and controversy. Some authors demonstrate that resistance to infection is attributed to a mixed Th1 and Th2 response and resistance to reinfection after repeated treatments through mechanisms associated with the Th2 response. Through flow cytometry, the phenotypic characterization of B and T lymphocytes in individuals residing in endemic areas with low parasite loads over 10 years was evaluated for the first time in humans. In this study, individuals with low parasite loads for Schistosoma mansoni had a higher proportion of Th1 and Th2 cells. In addition, lymphocytes from these individuals showed a higher degree of expression of costimulatory molecules CD28 and CTLA-4 and regulatory molecules FoxP3 and IL-10, when compared to individuals with high parasite loads. Our data indicate that the control of the parasite load of S. mansoni must be associated with a Th1, Th2, and regulatory response, and that further studies are needed to elucidate the possibility of mechanisms associated with the hyporesponsiveness of lymphocytes from individuals with high parasite loads.

Rituximab in glomerular diseases: a case series and narrative review

INTRODUCTION

The use of Rituximab (RTX) in glomerular diseases (GD) has increased in the past years, although it is still only used in a small fraction of patients.

METHODS

A single center retrospective study of adult patients with membranous nephropathy (MN), focal segmental glomerulosclerosis (FSGS), lupus nephritis (LN), and vasculitis treated with RTX as first or second-line therapy was conducted at our center from 2010 to 2020.

RESULTS

We identified 19 patients; 36.8% had MN and 25.0% each had FSGS, LN, and vasculitis. RTX was first-line therapy in 26.3% of patients and in 73.7% it was second-line therapy. Mean follow-up time was 7.7 ± 7.2 years. In MN, 2 patients (28.6%) had complete remission (CR), 2 patients (28.6%) had partial remission (PR), and 3 patients (42.9%) had no response (NR). In FSGS, 2 patients (50.0%) presented CR, 1 patient (25.0%) had no response, and 1 patient had renal deterioration. Two patients (50.0%) had a LN class IV with a CR after RTX, 1 patient with LN class IIIC/V had no response, and 1 patient with LN class II had renal deterioration. In vasculitis, 3 patients (75.0%) presented CR and 1 patient had PR. Infusion reactions were present in 2 patients (10.5%) and one patient had multiple infectious complications.

CONCLUSIONS

The efficacy of RTX in treating different types of immune-mediated GD has been demonstrated with different response rates, but an overall safe profile. In our case series, the results are also encouraging. Longitudinal studies are needed to better understand the effect of RTX in GD.

Follicular T cells are clonally and transcriptionally distinct in B cell-driven mouse autoimmune disease

Pathogenic autoantibodies contribute to tissue damage and clinical decline in autoimmune disease. Follicular T cells are central regulators of germinal centers, although their contribution to autoantibody-mediated disease remains unclear. Here we perform single cell RNA and T cell receptor (TCR) sequencing of follicular T cells in a mouse model of autoantibody-mediated disease, allowing for analyses of paired transcriptomes and unbiased TCRαβ repertoires at single cell resolution. A minority of clonotypes are preferentially shared amongst autoimmune follicular T cells and clonotypic expansion is associated with differential gene signatures in autoimmune disease. Antigen prediction using algorithmic and machine learning approaches indicates convergence towards shared specificities between non-autoimmune and autoimmune follicular T cells. However, differential autoimmune transcriptional signatures are preserved even amongst follicular T cells with shared predicted specificities. These results demonstrate that follicular T cells are phenotypically distinct in B cell-driven autoimmune disease, providing potential therapeutic targets to modulate autoantibody development.

Integrin CD11b Negatively Regulates B Cell Receptor Signaling to Shape Humoral Response during Immunization and Autoimmunity

Our previous work has revealed the ability of CD11b to regulate BCR signaling and control autoimmune disease in mice. However, how CD11b regulates the immune response under normal conditions remains unknown. Through the use of a CD11b knockout model on a nonautoimmune background, we demonstrated that CD11b-deficient mice have an elevated Ag-specific humoral response on immunization. Deletion of CD11b resulted in elevated low-affinity and high-affinity IgG Ab and increases in Ag-specific germinal center B cells and plasma cells (PCs). Examination of BCR signaling in CD11b-deficient mice revealed defects in association of negative regulators pLyn and CD22 with the BCR, but increases in colocalizations between positive regulator pSyk and BCR after stimulation. Using a CD11b-reporter mouse model, we identified multiple novel CD11b-expressing B cell subsets that are dynamically altered during immunization. Subsequent experiments using a cell-specific CD11b deletion model revealed this effect to be B cell intrinsic and not altered by myeloid cell CD11b expression. Importantly, CD11b expression on PCs also impacts on BCR repertoire selection and diversity in autoimmunity. These studies describe a novel role for CD11b in regulation of the healthy humoral response and autoimmunity, and reveal previously unknown populations of CD11b-expressing B cell subsets, suggesting a complex function for CD11b in B cells during development and activation.

Neoadjuvant Cabozantinib and Nivolumab Converts Locally Advanced HCC into Resectable Disease with Enhanced Antitumor Immunity

A potentially curative hepatic resection is the optimal treatment for hepatocellular carcinoma (HCC), but most patients are not candidates for resection and most resected HCCs eventually recur. Until recently, neoadjuvant systemic therapy for HCC has been limited by a lack of effective systemic agents. Here, in a single arm phase 1b study, we evaluated the feasibility of neoadjuvant cabozantinib and nivolumab in patients with HCC including patients outside of traditional resection criteria (NCT03299946). Of 15 patients enrolled, 12 (80%) underwent successful margin negative resection, and 5/12 (42%) patients had major pathologic responses. In-depth biospecimen profiling demonstrated an enrichment in T effector cells, as well as tertiary lymphoid structures, CD138+ plasma cells, and a distinct spatial arrangement of B cells in responders as compared to non-responders, indicating an orchestrated B-cell contribution to antitumor immunity in HCC.

Microbiota-Driven Activation of Intrahepatic B Cells Aggravates NASH Through Innate and Adaptive Signaling

BACKGROUND AND AIMS

Nonalcoholic steatohepatitis is rapidly becoming the leading cause of liver failure and indication for liver transplantation. Hepatic inflammation is a key feature of NASH but the immune pathways involved in this process are poorly understood. B lymphocytes are cells of the adaptive immune system that are critical regulators of immune responses. However, the role of B cells in the pathogenesis of NASH and the potential mechanisms leading to their activation in the liver are unclear.

APPROACH AND RESULTS

In this study, we report that NASH livers accumulate B cells with elevated pro-inflammatory cytokine secretion and antigen-presentation ability. Single-cell and bulk RNA sequencing of intrahepatic B cells from mice with NASH unveiled a transcriptional landscape that reflects their pro-inflammatory function. Accordingly, B-cell deficiency ameliorated NASH progression, and adoptively transferring B cells from NASH livers recapitulates the disease. Mechanistically, B-cell activation during NASH involves signaling through the innate adaptor myeloid differentiation primary response protein 88 (MyD88) as B cell-specific deletion of MyD88 reduced hepatic T cell-mediated inflammation and fibrosis, but not steatosis. In addition, activation of intrahepatic B cells implicates B cell-receptor signaling, delineating a synergy between innate and adaptive mechanisms of antigen recognition. Furthermore, fecal microbiota transplantation of human NAFLD gut microbiotas into recipient mice promoted the progression of NASH by increasing the accumulation and activation of intrahepatic B cells, suggesting that gut microbial factors drive the pathogenic function of B cells during NASH.

CONCLUSION

Our findings reveal that a gut microbiota-driven activation of intrahepatic B cells leads to hepatic inflammation and fibrosis during the progression of NASH through innate and adaptive immune mechanisms.

Effects of B cell-activating factor on tumor immunity

Immunotherapies that modulate T cell function have been firmly established as a pillar of cancer therapy, whereas the potential for B cells in the antitumor immune response is less established. B cell-activating factor (BAFF) is a B cell-activating cytokine belonging to the TNF ligand family that has been associated with autoimmunity, but little is known about its effects on cancer immunity. We find that BAFF upregulates multiple B cell costimulatory molecules; augments IL-12a expression, consistent with Be-1 lineage commitment; and enhances B cell antigen-presentation to CD4+ Th cells in vitro. In a syngeneic mouse model of melanoma, BAFF upregulates B cell CD40 and PD-L1 expression; it also modulates T cell function through increased T cell activation and TH1 polarization, enhanced expression of the proinflammatory leukocyte trafficking chemokine CCR6, and promotion of a memory phenotype, leading to enhanced antitumor immunity. Similarly, adjuvant BAFF promotes a memory phenotype of T cells in vaccine-draining lymph nodes and augments the antitumor efficacy of whole cell vaccines. BAFF also has distinct immunoregulatory functions, promoting the expansion of CD4+Foxp3+ Tregs in the spleen and tumor microenvironment (TME). Human melanoma data from The Cancer Genome Atlas (TCGA) demonstrate that BAFF expression is positively associated with overall survival and a TH1/IFN-γ gene signature. These data support a potential role for BAFF signaling as a cancer immunotherapy.

The role of B cell antigen presentation in the initiation of CD4+ T cell response

B cells have been known for their ability to present antigens to T cells for almost 40 years. However, the precise roles of B cell antigen presentation in various immune responses are not completely understood. The term "professional" antigen-presenting cells (APCs) was proposed to distinguish APCs that are required for initiating the immune responses from those use antigen presentation to enhance their own effector functions. Unlike dendritic cells, which are defined as professional APCs for their well-established functions in activating naive T cells, B cells have been shown in the past to mostly present antigens to activated CD4+ T cells mainly to seek help from T helper cells. However, recent evidence suggested that B cells can act as professional APCs under infectious conditions or conditions mimicking viral infections. B cell antigen receptors (BCRs) and the innate receptor Toll-like receptors are activated synergistically in response to pathogens or virus-like particles, under which conditions B cells are not only potent but also the predominant APCs to turn naive CD4+ T cells into T follicular helper cells. The discovery of B cells as professional APCs to initiate CD4+ T cell response provides a new insight for both autoimmune diseases and vaccine development.

Decrease in the proportion of CD24hi CD38hi B cells and impairment of their regulatory capacity in type 1 diabetes patients

B10 cells restore immune balance by producing interleukin (IL)-10. Impaired B10 cell responses are related to numerous autoimmune diseases. However, the function of B10 cells in type 1 diabetes (T1D) patients is controversial. We hypothesized that there are numerical and functional defects of B10 cells in T1D. Sixty-two patients with T1D and 74 healthy volunteers were included in our study. We showed that B10 cells in human peripheral blood belong to a CD24^hi CD38^hi B cell subpopulation. CD24^hi CD38^hi B cells from healthy individuals possessed regulatory capacity, suppressed interferon (IFN)-γ, tumor necrosis factor (TNF)-α and IL-17A production and promoted IL-4 production and forkhead box protein 3 (FoxP3) expression in CD4⁺ T cells through an IL-10-dependent mechanism. Compared to healthy controls, B10 cell percentages in T1D were significantly lower (5·6 ± 3·5 versus 6·9 ± 3·3%; P < 0·05), produced less IL-10 (15·4 ± 4·3 versus 29·0 ± 4·5%; P < 0·001) and lacked regulatory capacity. In addition, Pearson's correlation analysis showed that the frequency of circulating B10 cells was negatively correlated with the frequency of CD4⁺ IFN-γ⁺ and CD4⁺ TNF-α⁺ T cells (r = -0·248 and r = -0·283, P = 0·008 and P = 0·017, respectively), positively correlating with the frequency of CD4⁺ CD25⁺ FoxP3⁺ T cells (r = 0·247, P = 0·001). These data offer direct proof that there is a deficiency of circulating CD24^hi CD38^hi B cells in peripheral blood of patients with T1D, which participate in the T1D immune imbalance involved in the development of T1D.

Lessons from next generation influenza vaccines for inflammatory disease therapies

Lessons can be learned for treating inflammatory diseases such as rheumatoid arthritis (RA) from next generation approaches for development of universal influenza vaccines. Immunomodulation of inflammatory diseases, rather than ablation of cytokine or cellular responses, can address the root cause of the disease and provide potential cure. Like influenza, there are different antigenic 'strains' and inflammatory T cell responses, Th1 or Th17, that drive each person's disease. As such, next generation vaccine-like antigen specific therapies for inflammatory diseases can be developed but will need to be customized to the patient depending upon the antigen and T cell response that is driving the disease.

Immunological abnormalities in patients with primary biliary cholangitis

Primary biliary cholangitis (PBC), an autoimmune liver disease occurring predominantly in women, is characterized by high titers of serum anti-mitochondrial antibodies (AMAs) and progressive intrahepatic cholestasis. The immune system plays a critical role in PBC pathogenesis and a variety of immune cell subsets have been shown to infiltrate the portal tract areas of patients with PBC. Amongst the participating immune cells, CD4 T cells are important cytokine-producing cells that foster an inflammatory microenvironment. Specifically, these cells orchestrate activation of other immune cells, including autoreactive effector CD8 T cells that cause biliary epithelial cell (BEC) injury and B cells that produce large quantities of AMAs. Meanwhile, other immune cells, including dendritic cells (DCs), natural killer (NK) cells, NKT cells, monocytes, and macrophages are also important in PBC pathogenesis. Activation of these cells initiates and perpetuates bile duct damage in PBC patients, leading to intrahepatic cholestasis, hepatic damage, liver fibrosis, and eventually cirrhosis or even liver failure. Taken together, the body of accumulated clinical and experimental evidence has enhanced our understanding of the immunopathogenesis of PBC and suggests that immunotherapy may be a promising treatment option. Herein, we summarize current knowledge regarding immunological abnormalities of PBC patients, with emphasis on underlying pathogenic mechanisms. The differential immune response which occurs over decades of disease activity suggests that different therapies may be needed at different stages of disease.

Lupus nephritis and B-cell targeting therapy

INTRODUCTION

Lupus Nephritis (LN) is a severe manifestation of Systemic Lupus Erythematosus (SLE) with a significant prognostic impact. Over a prolonged course, an exhaustion of treatment alternatives may occur and further therapeutic options are needed. B cells play a pivotal role in disease pathogenesis and represent an attractive therapeutic target. Areas covered: This review provides an update regarding targeting B cells in LN. The rational for this approach, as well as currently available and future targets are discussed. Expert commentary: Despite its wide clinical use and the encouraging results from retrospective studies, a role of rituximab in LN has not been prospectively confirmed. Trial design methodologies as well as intrinsic limitations of this approach may be responsible and rituximab use is currently limited as a rescue treatment or in settings where a strong steroid sparing effect is warranted. Despite belimumab now being licensed for use in SLE, the evidence in LN is weak although prospective trials are on-going. The combination of different targeted approaches as well as a focus on new clinical end-points may be strategies to identify new therapeutic options.

Autoreactive helper T cells alleviate the need for intrinsic TLR signaling in autoreactive B cell activation

T cells play a significant role in the pathogenesis of systemic autoimmune diseases, including systemic lupus erythematosus; however, there is relatively little information on the nature and specificity of autoreactive T cells. Identifying such cells has been technically difficult because they are likely to be rare and low affinity. Here, we report a method for identifying autoreactive T cell clones that recognize proteins contained in autoantibody immune complexes, providing direct evidence that functional autoreactive helper T cells exist in the periphery of normal mice. These T cells significantly enhanced autoreactive B cell proliferation and altered B cell differentiation in vivo. Most importantly, these autoreactive T cells were able to rescue many aspects of the TLR-deficient AM14 (anti-IgG2a rheumatoid factor) B cell response, suggesting that TLR requirements can be bypassed. This result has implications for the efficacy of TLR-targeted therapy in the treatment of ongoing disease.

Efficient Culture of Human Naive and Memory B Cells for Use as APCs

The ability to culture and expand B cells in vitro has become a useful tool for studying human immunity. A limitation of current methods for human B cell culture is the capacity to support mature B cell proliferation. We developed a culture method to support the efficient activation and proliferation of naive and memory human B cells. This culture supports extensive B cell proliferation, with ∼10³-fold increases following 8 d in culture and 10⁶-fold increases when cultures are split and cultured for 8 more days. In culture, a significant fraction of naive B cells undergo isotype switching and differentiate into plasmacytes. Culture-derived (CD) B cells are readily cryopreserved and, when recovered, retain their ability to proliferate and differentiate. Significantly, proliferating CD B cells express high levels of MHC class II, CD80, and CD86. CD B cells act as APCs and present alloantigens and microbial Ags to T cells. We are able to activate and expand Ag-specific memory B cells; these cultured cells are highly effective in presenting Ag to T cells. We characterized the TCR repertoire of rare Ag-specific CD4⁺ T cells that proliferated in response to tetanus toxoid (TT) presented by autologous CD B cells. TCR Vβ usage by TT-activated CD4⁺ T cells differs from resting and unspecifically activated CD4⁺ T cells. Moreover, we found that TT-specific TCR Vβ usage by CD4⁺ T cells was substantially different between donors. This culture method provides a platform for studying the BCR and TCR repertoires within a single individual.

Revisiting the regulatory roles of the TGF-β family of cytokines

TGF-β family members are multipotent cytokines that are involved in many cellular processes, including cell differentiation, organ development, wound healing and immune regulation. TGF-β has pleiotropic effects on adaptive immunity, especially in the regulation of CD4(+) T cell and B cell responses. Furthermore, identification of CD4(+) T cell subsets that produce TGF-β3 revealed unexpected roles of TGF-β3 in the control of adaptive immunity. In contrast to TGF-β1, which induces extensive fibrosis, TGF-β3 induces non-scarring wound healing and counteracts tissue fibrosis. Recent progress in the understanding of the activation mechanism of TGF-β may enable us to develop novel biologic therapies based on advanced protein engineering.

Defects in lysosomal maturation facilitate the activation of innate sensors in systemic lupus erythematosus

Defects in clearing apoptotic debris disrupt tissue and immunological homeostasis, leading to autoimmune and inflammatory diseases. Herein, we report that macrophages from lupus-prone MRL/lpr mice have impaired lysosomal maturation, resulting in heightened ROS production and attenuated lysosomal acidification. Impaired lysosomal maturation diminishes the ability of lysosomes to degrade apoptotic debris contained within IgG-immune complexes (IgG-ICs) and promotes recycling and the accumulation of nuclear self-antigens at the membrane 72 h after internalization. Diminished degradation of IgG-ICs prolongs the intracellular residency of nucleic acids, leading to the activation of Toll-like receptors. It also promotes phagosomal membrane permeabilization, allowing dsDNA and IgG to leak into the cytosol and activate AIM2 and TRIM21. Collectively, these events promote the accumulation of nuclear antigens and activate innate sensors that drive IFNα production and heightened cell death. These data identify a previously unidentified defect in lysosomal maturation that provides a mechanism for the chronic activation of intracellular innate sensors in systemic lupus erythematosus.

Breakdown of Immune Tolerance in Systemic Lupus Erythematosus by Dendritic Cells

Dendritic cells (DC) play an important role in the pathogenesis of systemic lupus erythematosus (SLE), an autoimmune disease with multiple tissue manifestations. In this review, we summarize recent studies on the roles of conventional DC and plasmacytoid DC in the development of both murine lupus and human SLE. In the past decade, studies using selective DC depletions have demonstrated critical roles of DC in lupus progression. Comprehensive in vitro and in vivo studies suggest activation of DC by self-antigens in lupus pathogenesis, followed by breakdown of immune tolerance to self. Potential treatment strategies targeting DC have been developed. However, many questions remain regarding the mechanisms by which DC modulate lupus pathogenesis that require further investigations.

Therapeutic potential of regulatory cytokines that target B cells

Autoreactive B cells play a crucial role in the pathogenesis of autoimmune diseases by producing auto-antibodies and presenting antigens. Regulatory cytokines that simultaneously suppress multiple pathways have the potential to control autoreactive B cells. The generally inhibitory cytokine IL-10 may have a stimulatory effect on human B-cell survival and antibody production. TGF-β family cytokines can decrease or increase antibody production and can suppress B-cell proliferation and differentiation. In contrast to TGF-β1, which induces extensive fibrosis, TGF-β3 and bone morphogenetic protein 6 (BMP-6)/BMP-7 induce non-scarring wound healing and counteract tissue fibrosis. Therefore, TGF-β3 and BMP-6/BMP-7 may be clinically applicable as therapeutic cytokines that target B cells. Recent progress in protein engineering may enable us to generate novel biologic therapies based on TGF-β family cytokines.

B Cell-Specific MHC Class II Deletion Reveals Multiple Nonredundant Roles for B Cell Antigen Presentation in Murine Lupus

B cells have both Ab-dependent and Ab-independent functions in systemic autoimmune diseases, including systemic lupus erythematosus (SLE). Ab-independent functions are known to be important, because mice with B cells but no secreted Ig have severe disease. These functions could include roles in lymphoid development, cytokine secretion, and Ag presentation; however, these possibilities have not been directly tested in SLE models. In this study, we show by lineage-specific ablation of MHC class II (MHCII) that B cell Ag presentation plays a nonredundant role in CD4(+) T cell activation and effector differentiation in the MRL.Fas(lpr) mouse model of SLE. MHCII-mediated interactions between B and T cells further promote B cell proliferation and differentiation, and, in fact, inefficient MHCII deletion on B cells led to strong selection of escaped cells in activated and plasmablast compartments, further underscoring the central role of B cell Ag presentation. Despite the leakiness in the system, B cell-specific MHCII deletion resulted in substantially ameliorated clinical disease. Hence, B cell Ag presentation is critical for T and B cell activation and differentiation, as well as target organ damage.

Regulatory T cells in B-cell-deficient and wild-type mice differ functionally and in expression of cell surface markers

NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) with chronic inflammation of thyroids by T and B cells. B-cell deficient (B(-/-) ) mice are resistant to SAT but develop SAT if regulatory T (Treg) cells are transiently depleted. We established a transfer model using splenocytes from CD28(-/-)  B(-/-) mice (effector cells and antigen-presenting cells) cultured with or without sorted Treg cells from Foxp3-GFP wild-type (WT) or B(-/-) mice. After transfer to mice lacking T cells, mice given Treg cells from B(-/-) mice had significantly lower SAT severity scores than mice given Treg cells from WT mice, indicating that Treg cells in B(-/-) mice are more effective suppressors of SAT than Treg cells in WT mice. Treg cells from B(-/-) mice differ from WT Treg cells in expression of CD27, tumour necrosis factor receptor (TNFR) II p75, and glucocorticoid-induced TNFR-related protein (GITR). After transient depletion using anti-CD25 or diphtheria toxin, the repopulating Treg cells in B(-/-) mice lack suppressor function, and expression of CD27, GITR and p75 is like that of WT Treg cells. If B(-/-) Treg cells develop with B cells in bone marrow chimeras, their phenotype is like that of WT Treg cells. Addition of B cells to cultures of B(-/-) Treg and T effector cells abrogates their suppressive function and their phenotype is like that of WT Treg cells. These results establish for the first time that Treg cells in WT and B(-/-) mice differ both functionally and in expression of particular cell surface markers. Both properties are altered after transient depletion and repopulation of B(-/-) Treg cells, and by the presence of B cells during Treg cell development or during interaction with effector T cells.

Targeting Syk-activated B cells in murine and human chronic graft-versus-host disease

Novel therapies for chronic graft-versus-host disease (cGVHD) are needed. Aberrant B-cell activation has been demonstrated in mice and humans with cGVHD. Having previously found that human cGVHD B cells are activated and primed for survival, we sought to further evaluate the role of the spleen tyrosine kinase (Syk) in cGVHD in multiple murine models and human peripheral blood cells. In a murine model of multiorgan system, nonsclerodermatous disease with bronchiolitis obliterans where cGVHD is dependent on antibody and germinal center (GC) B cells, we found that activation of Syk was necessary in donor B cells, but not T cells, for disease progression. Bone marrow-specific Syk deletion in vivo was effective in treating established cGVHD, as was a small-molecule inhibitor of Syk, fostamatinib, which normalized GC formation and decreased activated CD80/86(+) dendritic cells. In multiple distinct models of sclerodermatous cGVHD, clinical and pathological disease manifestations were not eliminated when mice were therapeutically treated with fostamatinib, though both clinical and immunologic effects could be observed in one of these scleroderma models. We further demonstrated that Syk inhibition was effective at inducing apoptosis of human cGVHD B cells. Together, these data demonstrate a therapeutic potential of targeting B-cell Syk signaling in cGVHD.

Long-lasting uveitis remission and hearing loss recovery after rituximab in Vogt-Koyanagi-Harada disease

Vogt-Koyanagi-Harada disease (VKHD) is a multisystemic disorder characterized by granulomatous panuveitis variably combined with T cell-mediated neurologic and cutaneous manifestations. Early and aggressive treatment with systemic corticosteroids is the mainstay of treatment for VKHD. Additional use of immunosuppressants, intravenous immunoglobulins, and tumor necrosis factor-alpha inhibitors can help the most severely affected patients and work as corticosteroid-sparing agents. We report the case of a young woman with relapsing and multiresistant VKHD who demonstrated a stable remission of both uveitis and high-frequency hearing loss following rituximab intravenous administration (1 g. twice, 2 weeks apart, and 6 months later). A complete clinical response was observed 1 month since the first infusion, and no ocular relapses were recorded during the following year; in addition, audiometry showed a high-frequency hearing recovery in the right ear. Further observational studies are required to define the role of CD20 inhibition in the management of VKHD.

Transfer of antigen from human B cells to dendritic cells

The cooperation of B lymphocytes with other antigen presenting cells (APCs) is often necessary in the efficient processing and presentation of antigen. Herein, we describe a mechanism by which B cells physically interact with dendritic cells (DCs) resulting in the transfer of B cell receptor (BCR)-enriched antigen to these APCs. Antigen transfer involves direct contact between the two cells followed by the capture of B cell derived membrane and intracellular components. Strikingly, DCs acquire greater amounts of antigen by transfer from B cells than by endocytosis of free antigen. Blocking scavenger receptor A, a DC surface receptor involved in membrane acquisition, abrogates these events. We propose that antigen transfer from B cells to DCs results in a more focused immunologic response due to the selective editing of Ag by the BCR.

Antigen-specific B lymphocytes acquire proteoglycan aggrecan from cartilage extracellular matrix resulting in antigen presentation and CD4+ T-cell activation

The majority of studies examining antigen-presenting cell (APC) function have focused on the capture and presentation of antigens released from pathogens or damaged cells. However, antigen-specific B cells are also capable of efficiently extracting antigens that are either tethered to, or integrally part of the plasma membrane of various target cells. In this study we show that B cells are also highly efficient at extracting integral components of the extracellular matrix (ECM) for subsequent presentation. In particular we demonstrate that B cells specific for aggrecan, an integral component of cartilage ECM, acquire this rheumatoid arthritis candidate autoantigen in both a B-cell-receptor-dependent and a contact-dependent manner. We also demonstrate that the subsequent presentation of aggregan from ECM leads to CD4(+) T-cell activation and effector cell formation. Recent studies have identified B-cell-mediated antigen presentation as essential for the development of autoimmunity, but a unique role for B cells compared with other APC has yet to be defined. Our findings lead us to propose that the acquisition of ECM-derived autoantigens represents a mechanism that defines the APC requirement for B cells in the development of autoimmunity.

B-cell depletion improves islet allograft survival with anti-CD45RB

A short course of anti-CD45RB leads to long-term islet allograft survival and donor-specific tolerance in approximately half of immunocompetent mice. We have previously demonstrated that anti-CD45RB antibody-mediated tolerance requires B-cells for cardiac allograft survival. We therefore asked whether B-cells were also required for anti-CD45RB antibody-mediated survival of islets. Unexpectedly, we found that nearly 100% of islet allografts survive long term in B-cell-deficient mice. Similarly, B-cell depletion by anti-CD22/cal augmented anti-CD45RB-mediated tolerance when administered pretransplant, although it had no effect on tolerance induction when administered posttransplant. Our results demonstrate that the role of B-cells in promoting tolerance with anti-CD45RB is graft specific, promoting tolerance in cardiac grafts but resisting tolerance in islet transplantation. These findings may help elucidate the varied action of B-cells in promoting tolerance versus rejection.

Autoantigens: novel forms and presentation to the immune system

It is clear that lupus autoimmunity is marked by a variety of abnormalities, including those found at a macroscopic scale, cells and tissues, as well as more microenvironmental influences, originating at the individual cell surface through to the nucleus. The convergence of genetic, epigenetic, and perhaps environmental influences all lead to the overt clinical expression of disease, reflected by the presences of autoantibodies and tissue pathology. This review will address several specific areas that fall among the non-genetic factors that contribute to lupus autoimmunity and related syndromes. In particular, we will discuss the importance of understanding various protein post-translational modifications (PTMs), mechanisms that mediate the ability of "modified self" to trigger autoimmunity, and how these PTMs influence lupus diagnosis. Finally, we will discuss altered pathways of autoantigen presentation that may contribute to the perpetuation of chronic autoimmune disease.

Transient depletion of CD4+ CD25+ regulatory T cells results in multiple autoimmune diseases in wild-type and B-cell-deficient NOD mice

Approximately 80% of female wild-type non-obese diabetic (WT NOD) mice spontaneously develop diabetes, whereas B-cell-deficient (B(-/-)) NOD mice are resistant to diabetes. B(-/-) mice are also resistant to other spontaneous and experimentally induced autoimmune diseases, including arthritis, systemic lupus erythematosus, Sjögren syndrome and thyroiditis. Under normal conditions, activation of self-reactive T cells in the periphery is limited by CD4(+) CD25(+) natural regulatory T (Treg) cells. B(-/-) NOD.H-2h4 mice, normally resistant to spontaneous autoimmune thyroiditis (SAT), develop SAT when Treg cells are depleted, suggesting that Treg cells are preferentially activated when autoantigen is initially presented by non-B-cell antigen-presenting cells. To test the hypothesis that increased Treg cell activity in B(-/-) mice contributes to their resistance to other autoimmune diseases, WT and B(-/-) NOD mice were given anti-CD25 to transiently deplete CD4(+) CD25(+) Treg cells. The WT and B(-/-) NOD mice given anti-CD25 developed diabetes much earlier than WT mice given rat IgG, whereas rat IgG-treated B(-/-) mice did not develop diabetes. Treg-cell-depleted mice had increased lymphocyte infiltration of the pancreas, salivary glands and thyroid compared with controls given rat IgG. These results are consistent with the hypothesis that resistance of B-cell-deficient NOD mice to several autoimmune diseases is due to the activity of Treg cells.

Cutting edge: Conditional MHC class II expression reveals a limited role for B cell antigen presentation in primary and secondary CD4 T cell responses

The activation, differentiation, and subsequent effector functions of CD4 T cells depend on interactions with a multitude of MHC class II (MHCII)-expressing APCs. To evaluate the individual contribution of various APCs to CD4 T cell function, we have designed a new murine tool for selective in vivo expression of MHCII in subsets of APCs. Conditional expression of MHCII in B cells was achieved using a cre-loxP approach. After i.v. or s.c. priming, partial proliferation and activation of CD4 T cells was observed in mice expressing MHCII only by B cells. Restricting MHCII expression to B cells constrained secondary CD4 T cell responses in vivo, as demonstrated in a CD4 T cell-dependent model of autoimmunity, experimental autoimmune encephalomyelitis. These results highlight the limitations of B cell Ag presentation during initiation and propagation of CD4 T cell function in vivo using a novel system to study individual APCs by the conditional expression of MHCII.

Regulatory B cells in autoimmune diseases

B cells are generally considered to be positive regulators of the immune response because of their capability to produce antibodies, including autoantibodies. The production of antibodies facilitates optimal CD4(+) T-cell activation because B cells serve as antigen-presenting cells and exert other modulatory functions in immune responses. However, certain B cells can also negatively regulate the immune response by producing regulatory cytokines and directly interacting with pathogenic T cells via cell-to-cell contact. These types of B cells are defined as regulatory B (Breg) cells. The regulatory function of Breg cells has been demonstrated in mouse models of inflammation, cancer, transplantation, and particularly in autoimmunity. In this review, we focus on the recent advances that lead to the understanding of the development and function of Breg cells and the implications of B cells in human autoimmune diseases.

B cells as effectors and regulators of sex-biased arthritis

B cells have been implicated both with pathogenic as well as protective capabilities in induction and regulation of autoimmune diseases. Rheumatoid arthritis (RA) is an autoimmune disease that occurs more often in women than men. A significant role of B cells as antibody producing and antigen-presenting cells has been demonstrated in RA. Predisposition to RA is associated with the presence of certain HLA class II alleles that share sequences with DRB1*0401. To determine the role of HLA genes and B cells in vivo, we have generated transgenic mice carrying HLA genes, DRB1*0401 and DQ8, known to be associated with susceptibility to RA. Humanized mice can be induced to develop arthritis that mimics human disease in clinical, histopathological and sex bias. Effect of hormones on immune cells and their function has been described in humans and mice and has been suggested to be the major reason for female bias of autoimmune diseases. An immune response to an antigen requires presentation by HLA molecules thus suggesting a critical role of MHC in combination with sex hormones in susceptibility to develop rheumatoid arthritis. Based on our observations, we hypothesize that modulation of B cells by estrogen, presentation of modified antigens by DR4 and production of antigen-specific B cell modulating cytokines leads to autoreactivity in females. These data suggest that considering patient's sex may be crucial in selecting the optimal treatment strategy. Humanized mice expressing RA susceptible and resistant haplotype provide a means to investigate mechanism sex-bias of arthritis and future strategies for therapy.

The immunosuppressive factors IL-10, TGF-β, and VEGF do not affect the antigen-presenting function of CD40-activated B cells

Background

Progress in recent years strengthened the concept of cellular tumor vaccinations. However, a crucial barrier to successful cancer immunotherapy is tumor-mediated immunosuppression. Tumor-derived soluble factors such as IL-10, TGF-β, and VEGF suppress effector cells either directly or indirectly by disruption of dendritic cell (DC) differentiation, migration and antigen presentation. Human B cells acquire potent immunostimulatory properties when activated via CD40 and have been shown to be an alternative source of antigen-presenting cells (APCs) for cellular cancer vaccines. Nevertheless, in contrast to DCs little knowledge exists about their susceptibility to tumor derived immunosuppressive factors. Thus, we assessed whether IL-10, TGF-β, or VEGF do affect key aspects of the immunostimulatory function of human CD40-activated B cells.

Methods

Cell surface expression of adhesion and costimulatory molecules and the proliferation capacity of CD40-activated B cells were compared to untreated controls by flow cytometry. Migration towards important chemokines of secondary lymph organs was measured with or without exposure to the immunosuppressive cytokines. Finally, an influence on T cell stimulation was investigated by allogeneic mixed lymphocyte reactions. For statistical analysis Student’s t test or two-way analysis of variance followed by Bonferroni's post-hoc test was used to compare groups. P values of <0.05 were considered statistically significant.

Results

Neither cell adhesion nor the expression of MHC class II and costimulatory molecules CD80 and CD86 was inhibited by addition of IL-10, TGF-β, or VEGF. Likewise, the proliferation of CD40-activated B cells was not impaired. Despite being exposed to IL-10, TGF-β, or VEGF the B cells migrated equally well as untreated controls to the chemokines SLC and SDF-1α. Most importantly, the capacity of CD40-activated B cells to stimulate CD4⁺ and CD8⁺ T cells remained unaffected.

Conclusion

Our findings suggest that key immunostimulatory functions of CD40-activated B cells are resistant to inhibition by the immunosuppressive factors IL-10, TGF-β, and VEGF. This supports considerations to use ex vivo generated CD40-activated B cells as a promising alternative or additional APC for cellular immunotherapy, especially in settings where these immunosuppressive cytokines are present in tumor environment.

Rituximab in children with resistant idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome resistant to standard treatments remains a therapeutic dilemma in pediatric nephrology. To test whether the anti-CD20 monoclonal antibody rituximab may benefit these patients, we conducted an open-label, randomized, controlled trial in 31 children with idiopathic nephrotic syndrome unresponsive to the combination of calcineurin inhibitors and prednisone. All children continued prednisone and calcineurin inhibitors at the doses prescribed before enrollment, and one treatment group received two doses of rituximab (375 mg/m(2) intravenously) as add-on therapy. The mean age was 8 years (range, 2-16 years). Rituximab did not reduce proteinuria at 3 months (change, -12% [95% confidence interval, -73% to 110%]; P=0.77 in analysis of covariance model adjusted for baseline proteinuria). Additional adjustment for previous remission and interaction terms (treatment by baseline proteinuria and treatment by previous remission) did not change the results. In conclusion, these data do not support the addition of rituximab to prednisone and calcineurin inhibitors in children with resistant idiopathic nephrotic syndrome.

Presentation of the candidate rheumatoid arthritis autoantigen aggrecan by antigen-specific B cells induces enhanced CD4(+) T helper type 1 subset differentiation

Effective immune responses require antigen uptake by antigen-presenting cells (APC), followed by controlled endocytic proteolysis resulting in the generation of antigen-derived peptide fragments that associate with intracellular MHC class II molecules. The resultant peptide-MHC class II complexes then move to the APC surface where they activate CD4(+) T cells. Dendritic cells (DC), macrophages and B cells act as efficient APC. In many settings, including the T helper type 1 (Th1) -dependent, proteoglycan-induced arthritis model of rheumatoid arthritis, accumulating evidence demonstrates that antigen presentation by B cells is required for optimal CD4(+) T cell activation. The reasons behind this however, remain unclear. In this study we have compared the activation of CD4(+) T cells specific for the proteoglycan aggrecan following antigen presentation by DC, macrophages and B cells. We show that aggrecan-specific B cells are equally efficient APC as DC and macrophages and use similar intracellular antigen-processing pathways. Importantly, we also show that antigen presentation by aggrecan-specific B cells to TCR transgenic CD4(+) T cells results in enhanced CD4(+) T cell interferon-γ production and Th1 effector sub-set differentiation compared with that seen with DC. We conclude that preferential CD4(+) Th1 differentiation may define the requirement for B cell APC function in both proteoglycan-induced arthritis and rheumatoid arthritis.

An obligatory role for lung infiltrating B cells in the immunopathogenesis of obliterative airway disease induced by antibodies to MHC class I molecules

Using a murine model, we demonstrated that endobronchial administration of antibodies (Abs) to major histocompatibility complex (MHC) class I results in cellular infiltration, epithelial metaplasia, fibrosis and obstruction of the small airways (obliterative airway disease [OAD]) mediated predominantly by Th17 responses to self-antigens. This resembles bronchiolitis obliterans syndrome developed following human lung transplantation. Since B cells play a crucial role in induction of autoimmune responses, we defined the role of B cells and its antigen presenting properties in induction of OAD in this study. Anti-MHC class I was administered endobronchially in B(-/-) and wild-type mice. In contrast to wild type, B(-/-) animals did not demonstrate cellular infiltration, epithelial metaplasia and obstruction of airways following anti-MHC. Frequency of K-α1 tubulin and CollagenV-specific IL-17 cells was significantly decreased in B(-/-) mice. As expected, Abs against self-antigens and germinal center formation were not developed in B(-/-) mice. Thus, we conclude that B cells and its antigen presenting capacity play an important role in induction of immune responses to self-antigens and immunopathogenesis of OAD following the administration of anti-MHC. Therefore, strategies to block B-cell and its antigen presenting functions should be considered for preventing the development of chronic rejection.

Transient depletion of B cells in young mice results in activation of regulatory T cells that inhibit development of autoimmune disease in adults

B-cell depletion therapy can be effective for treating B-cell lymphomas as well as many human and murine autoimmune diseases. B-cell-deficient mice are normally resistant to spontaneous autoimmune thyroiditis (SAT), but they develop SAT if regulatory T cells are transiently depleted during the first 3-6 weeks after birth. This was also a critical time when B-cell depletion effectively inhibited development of SAT in adult mice. The current study was undertaken to test the hypothesis that transient depletion of B cells using anti-CD20 would be sufficient to suppress SAT if B cells were depleted early in life and that inhibition of SAT would be due to the activity of Treg that functioned most effectively when B cells were absent or low. The results presented here support this hypothesis and indicate that development of autoimmune disease in adults is effectively inhibited when anti-CD20 is administered 1-3 weeks after birth. After 3 weeks, transient B-cell depletion is no longer effective, and B-cell depletion must be maintained to effectively suppress autoimmune disease. B-cell depletion in 1- to 3-week-old mice depletes all B-cell subsets, whereas B-cell depletion initiated in adults spares many marginal zone B cells. Following early B-cell depletion, splenic Treg increase in number, and depletion of Treg reverses the inhibitory effect of anti-CD20 on disease development. Early transient depletion of B cells could be useful for preventing autoimmune disease in individuals at high risk for developing autoimmune diseases as adults.

B-cell numbers and phenotype at clinical relapse following rituximab therapy differ in SLE patients according to anti-dsDNA antibody levels

Objectives. To correlate the kinetics of B-cell repopulation with relapse after B-cell depletion therapy in SLE patients and address whether variation in relapse rate, B-cell numbers and phenotype are related to anti-dsDNA antibody levels.

Methods. Sixty-one patients with refractory SLE were treated with a standard rituximab regimen. Clinical and serological measures of disease activity and B-cell numbers were assessed. B-cell phenotype was examined in a subgroup of patients by flow cytometry.

Results. Disease relapse was substantially delayed beyond B-cell repopulation, and early relapse was associated with a faster rate of repopulation. At relapse, B-cell numbers were significantly lower than at baseline in patients with high anti-dsDNA antibody levels (>100 IU/ml) but not in patients with low anti-dsDNA antibody levels. Of the patients with high anti-dsDNA antibodies at baseline, levels fell significantly only in those patients who remained in remission after repopulation. Relapse with high anti-dsDNA antibody levels was associated with an increased percentage of IgD⁻CD27^hi plasmablasts, whereas relapse with low anti-dsDNA antibody levels was accompanied by an increased percentage of IgD⁻CD27⁻ B cells.

Conclusion. Anti-dsDNA antibody levels distinguished two patient groups, which differ in their B-cell number and phenotype at relapse following rituximab, and suggest that different B-cell pathologies exist in SLE. The data imply that B-cell numbers should be kept very low for a sustained period in patients with high dsDNA binding, therefore justifying a more aggressive regimen.

Inhibition of antigen trafficking through scavenger receptor A

B cell acquisition and presentation of specific autoantigens (auto-Ags) are thought to play an important and complex role in autoimmunity development. We previously identified scavenger receptor A (SR-A) as an early target in altering B cell-mediated autoimmunity. SR-A is highly expressed on professional antigen-presenting cells such as macrophages (MΦs) and dendritic cells (DCs). In this study, we demonstrate that SR-A is responsible for controlling B cell interactions with DCs/MΦs to promote Ag transfer from B cells to DCs/MΦs. We established a high-throughput ELISA-based screen to identify novel SR-A inhibitors, the specificity of which was determined by dose dependence and Biacore surface plasmon resonance testing. We identified small molecule inhibitors (SMIs) able to reduce SR-A-mediated Ag transfer in human cells. In particular, the SMIs prevented SR-A-positive cells from accumulating/loading Ag over time. Furthermore, we determined that one SMI, sennoside B, can reduce SR-A-mediated capture of B cells. Finally, SMI-mediated decreases in Ag transfer or accumulation reduced T cell proliferation in vitro and in vivo. These observations demonstrate that B cell-DC/MΦ interactions are conducive to promoting Ag trafficking between these cell types via SR-A. Inhibitors of SR-A may provide a novel therapeutic strategy in ameliorating autoimmune disease development.