Toll-like receptor 7 (TLR7)-driven accumulation of a novel CD11c⁺ B-cell population is important for the development of autoimmunity

Aging and respiratory viral infection: from acute morbidity to chronic sequelae

The altered immune response in aged hosts play a vital role in contributing to their increased morbidity and mortality during respiratory virus infections. The aged hosts display impaired antiviral immune response as well as increased risk for long-term pulmonary sequelae post virus clearance. However, the underlying cellular and molecular mechanisms driving these alterations of the immune compartment have not been fully elucidated. During the era of COVID-19 pandemic, a better understanding of such aspects is urgently needed to provide insight that will benefit the geriatric patient care in prevention as well as treatment. Here, we review the current knowledge about the unique immune characteristics of aged hosts during homeostasis and respiratory virus infections.

T-bet+CD27+CD21- B cells poised for plasma cell differentiation during antibody-mediated rejection of kidney transplants

Alloimmune responses driven by donor-specific antibodies (DSAs) can lead to antibody-mediated rejection (ABMR) in organ transplantation. Yet, the cellular states underlying alloreactive B cell responses and the molecular components controlling them remain unclear. Using high-dimensional profiling of B cells in a cohort of 96 kidney transplant recipients, we identified expanded numbers of CD27⁺CD21^– activated memory (AM) B cells that expressed the transcription factor T-bet in patients who developed DSAs and progressed to ABMR. Notably, AM cells were less frequent in DSA⁺ABMR^– patients and at baseline levels in DSA^– patients. RNA-Seq analysis of AM cells in patients undergoing ABMR revealed these cells to be poised for plasma cell differentiation and to express restricted IGHV sequences reflective of clonal expansion. In addition to T-bet, AM cells manifested elevated expression of interferon regulatory factor 4 and Blimp1, and upon coculture with autologous T follicular helper cells, differentiated into DSA-producing plasma cells in an IL-21–dependent manner. The frequency of AM cells was correlated with the timing and severity of ABMR manifestations. Importantly, T-bet⁺ AM cells were detected within kidney allografts along with their restricted IGHV sequences. This study delineates a pivotal role for AM cells in promoting humoral responses and ABMR in organ transplantation and highlights them as important therapeutic targets.

The Multiple Roles of B Cells in the Pathogenesis of Sjögren's Syndrome

Primary Sjögren’s syndrome (pSS) is a chronic autoimmune disease characterized by lymphocytic infiltration and tissue destruction of exocrine glands such as salivary glands. Although the formation of ectopic lymphoid tissue in exocrine glands and overproduction of autoantibodies by autoreactive B cells highlight the critical involvement of B cells in disease development, the precise roles of various B cell subsets in pSS pathogenesis remain partially understood. Current studies have identified several novel B cell subsets with multiple functions in pSS, among which autoreactive age-associated B cells, and plasma cells with augmented autoantibody production contribute to the disease progression. In addition, tissue-resident Fc Receptor-Like 4 (FcRL4)⁺ B cell subset with enhanced pro-inflammatory cytokine production serves as a key driver in pSS patients with mucosa-associated lymphoid tissue (MALT)-lymphomas. Recently, regulatory B (Breg) cells with impaired immunosuppressive functions are found negatively correlated with T follicular helper (Tfh) cells in pSS patients. Further studies have revealed a pivotal role of Breg cells in constraining Tfh response in autoimmune pathogenesis. This review provides an overview of recent advances in the identification of pathogenic B cell subsets and Breg cells, as well as new development of B-cell targeted therapies in pSS patients.

Heterogeneity of meningeal B cells reveals a lymphopoietic niche at the CNS borders

The meninges contain adaptive immune cells that provide immunosurveillance of the central nervous system (CNS). These cells are thought to derive from the systemic circulation. Through single-cell analyses, confocal imaging, bone marrow chimeras, and parabiosis experiments, we show that meningeal B cells derive locally from the calvaria, which harbors a bone marrow niche for hematopoiesis. B cells reach the meninges from the calvaria through specialized vascular connections. This calvarial-meningeal path of B cell development may provide the CNS with a constant supply of B cells educated by CNS antigens. Conversely, we show that a subset of antigen-experienced B cells that populate the meninges in aging mice are blood-borne. These results identify a private source for meningeal B cells, which may help maintain immune privilege within the CNS.

Latent gammaherpesvirus exacerbates arthritis through modification of age-associated B cells

Epstein-Barr virus (EBV) infection is associated with rheumatoid arthritis (RA) in adults, though the nature of the relationship remains unknown. Herein, we have examined the contribution of viral infection to the severity of arthritis in mice. We have provided the first evidence that latent gammaherpesvirus infection enhances clinical arthritis, modeling EBV's role in RA. Mice latently infected with a murine analog of EBV, gammaherpesvirus 68 (γHV68), develop more severe collagen-induced arthritis and a Th1-skewed immune profile reminiscent of human disease. We demonstrate that disease enhancement requires viral latency and is not due to active virus stimulation of the immune response. Age-associated B cells (ABCs) are associated with several human autoimmune diseases, including arthritis, though their contribution to disease is not well understood. Using ABC knockout mice, we have provided the first evidence that ABCs are mechanistically required for viral enhancement of disease, thereby establishing that ABCs are impacted by latent gammaherpesvirus infection and provoke arthritis.

Potential Relevance of B-cell Maturation Pathways in Defining the Cell(s) of Origin for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a common, incurable disease of undefined cause. Notably, the normal cell equivalents of CLL cells remain elusive, and it is possible that the disease emanates from several normal B-cell subsets. This article reviews the literature relating to this issue, focusing on recent findings, in particular made through epigenetic analyses that strongly support the disease developing from a normal Ag-experienced and memory cell-like B lymphocyte. It also reports the known pathways whereby normal B lymphocytes mature after antigenic challenge and proposes that this information is relevant in defining the cells of origin of this disease.

Initial observations on age, gender, BMI and hypertension in antibody responses to SARS-CoV-2 BNT162b2 vaccine

BACKGROUND

Literature data suggests that age, gender and body mass index (BMI) could be associated with difference in immune responses to vaccines. The first goal of the study was to analyze the antibody titre seven days after the second dose of BNT162b2 vaccine in a group of 248 healthcare workers (HCWs). The second goal was to analyze how antibody titre changes in correlation with age, gender, BMI and hypertension.

METHODS

An immunogenicity evaluation was carried out among HCWs vaccinated at the Istituti Fisioterapici Ospitalieri (IFO), Rome, Italy. All HCWs were asked to be vaccinated by the Italian national vaccine campaign at the beginning of 2021. 260 vaccinated HCWs were enrolled in the study. All eligible participants were assigned to receive the priming dose in two weeks' time and the booster dose exactly 21 days thereafter. Blood and nasopharyngeal swabs were collected at baseline and 7 days after second dose of vaccine. Quantitative measurements of IgG antibodies against S1/S2 antigens of SARS-CoV-2 were performed with a commercial chemiluminescent immunoassay. Presence of SARS-Cov-2 in nasopharyngeal swab was determined by commercial RT-PCR testing.

FINDINGS

248 HWCs were analyzed, 158 women (63.7%) and 90 men (36.3%). After the second dose of BNT162b2 vaccine, 99.5% of participants developed a humoral immune response. The geometric mean concentration of antibodies among the vaccinated subjects after booster dose (285.9 AU/mL 95% CI: 249.5-327.7) was higher than that of human convalescent sera (39.4 AU/mL, 95% CI: 33.1-46.9), with p<0.0001. Multivariate linear regression analysis of AU/mL by age, gender and BMI multivariate was performed by the inclusion of covariates. This analysis demonstrated that age (p<0.0001) and gender (p = 0.038) are statistically associated with differences in antibody response after vaccination, whereas BMI and hypertension have no statistically significant association (p = 0.078 and p = 0.52 respectively).

INTERPRETATION

99.5% of HCW developed a humoral immune response and female and young participants seem to have an increased capacity to mount humoral immune responses. BMI and hypertension seem not associated with difference in immune response to the vaccine.

FUNDING

None.

Epigenetic Plasticity Enables CNS-Trafficking of EBV-infected B Lymphocytes

Subpopulations of B-lymphocytes traffic to different sites and organs to provide diverse and tissue-specific functions. Here, we provide evidence that epigenetic differences confer a neuroinvasive phenotype. An EBV+ B cell lymphoma cell line (M14) with low frequency trafficking to the CNS was neuroadapted to generate a highly neuroinvasive B-cell population (MUN14). MUN14 B cells efficiently infiltrated the CNS within one week and produced neurological pathologies. We compared the gene expression profiles of viral and cellular genes using RNA-Seq and identified one viral (EBNA1) and several cellular gene candidates, including secreted phosphoprotein 1/osteopontin (SPP1/OPN), neuron navigator 3 (NAV3), CXCR4, and germinal center-associated signaling and motility protein (GCSAM) that were selectively upregulated in MUN14. ATAC-Seq and ChIP-qPCR revealed that these gene expression changes correlated with epigenetic changes at gene regulatory elements. The neuroinvasive phenotype could be attenuated with a neutralizing antibody to OPN, confirming the functional role of this protein in trafficking EBV+ B cells to the CNS. These studies indicate that B-cell trafficking to the CNS can be acquired by epigenetic adaptations and provide a new model to study B-cell neuroinvasion associated CNS lymphoma and autoimmune disease of the CNS, including multiple sclerosis (MS).

Chess Not Checkers: Complexities Within the Myeloid Response to the Acute Kidney Injury Syndrome

Immune dysregulation in acute kidney injury (AKI) is an area of intense interest which promises to enhance our understanding of the disease and how to manage it. Macrophages are a heterogeneous and dynamic population of immune cells that carry out multiple functions in tissue, ranging from maintenance to inflammation. As key sentinels of their environment and the major immune population in the uninjured kidney, macrophages are poised to play an important role in the establishment and pathogenesis of AKI. These cells have a profound capacity to orchestrate downstream immune responses and likely participate in skewing the kidney environment toward either pathogenic inflammation or injury resolution. A clear understanding of macrophage and myeloid cell dynamics in the development of AKI will provide valuable insight into disease pathogenesis and options for intervention. This review considers evidence in the literature that speaks to the role and regulation of macrophages and myeloid cells in AKI. We also highlight barriers or knowledge gaps that need to be addressed as the field advances.

Aging and Options to Halt Declining Immunity to Virus Infections

Immunosenescence is a process associated with aging that leads to dysregulation of cells of innate and adaptive immunity, which may become dysfunctional. Consequently, older adults show increased severity of viral and bacterial infections and impaired responses to vaccinations. A better understanding of the process of immunosenescence will aid the development of novel strategies to boost the immune system in older adults. In this review, we focus on major alterations of the immune system triggered by aging, and address the effect of chronic viral infections, effectiveness of vaccination of older adults and strategies to improve immune function in this vulnerable age group.

Older adults: panoramic view on the COVID-19 vaccination

In December 2020, COVID-19 vaccination started in many countries, with which the world community hopes to stop the further spread of the current pandemic. More than 90% of sick and deceased patients belong to the category of older adults (65 years and older). This category of the population is most vulnerable to infectious diseases, so vaccination is the most effective preventive strategy, the need for which for older adults is indisputable. Here we briefly summarize information about age-related changes in the immune system and present current data on their impact on the formation of the immune response to vaccination. Older age is accompanied by the process of biological aging accompanied by involution of the immune system with increased susceptibility to infections and a decrease in the effect of immunization. Therefore, in the ongoing mass COVID-19 vaccination, the older adults are a growing public health concern. The authors provide an overview of the various types of COVID-19 vaccines approved for mass immunization of the population by the end of 2020, including older adults, as well as an overview of strategies and platforms to improve the effectiveness of vaccination of this population. In the final part, the authors propose for discussion a system for assessing the safety and monitoring the effectiveness of COVID-19 vaccines for the older adults.

Regnase-1 is essential for B cell homeostasis to prevent immunopathology

Regnase-1 is an emerging regulator of immune responses with essential roles in the posttranscriptional control of immune cell activation. Regnase-1 is expressed in B cells; however, its B cell-specific functions remain unknown. Here, we demonstrate that Regnase-1 prevents severe autoimmune pathology and show its essential role in maintaining B cell homeostasis. Using Cre driver mice for ablation of Regnase-1 at various stages of B cell development, we demonstrate that loss of Regnase-1 leads to aberrant B cell activation and differentiation, resulting in systemic autoimmunity and early morbidity. The basis of these findings was informed by gene expression data revealing a regulatory role for Regnase-1 in the suppression of a transcriptional program that promotes B cell activation, survival, and differentiation. Overall, our study shows that Regnase-1 exerts critical control of B cell activation, which is required for prevention of immunopathology.

The dangers of déjà vu: memory B cells as the cells of origin of ABC-DLBCLs

Activated B-cell (ABC)-diffuse large B-cell lymphomas (DLBCLs) are clinically aggressive and phenotypically complex malignancies, whose transformation mechanisms remain unclear. Partially differentiated antigen-secreting cells (plasmablasts) have long been regarded as cells-of-origin for these tumors, despite lack of definitive experimental evidence. Recent DLBCL reclassification based on mutational landscapes identified MCD/C5 tumors as specific ABC-DLBCLs with unfavorable clinical outcome, activating mutations in the signaling adaptors MYD88 and CD79B, and immune evasion through mutation of antigen-presenting genes. MCD/C5s manifest prominent extranodal dissemination and similarities with primary extranodal lymphomas (PENLs). In this regard, recent studies on TBL1XR1, a gene recurrently mutated in MCD/C5s and PENLs, suggest that aberrant memory B cells (MBs), and not plasmablasts, are the true cells-of-origin for these tumors. Moreover, transcriptional and phenotypic profiling suggests that MCD/C5s, as a class, represent bona fide MB tumors. Based on emerging findings we propose herein a generalized stepwise model for MCD/C5 and PENLs pathogenesis, whereby acquisition of founder mutations in activated B cells favors the development of aberrant MBs prone to avoid plasmacytic differentiation on recall and undergo systemic dissemination. Cyclic reactivation of these MBs through persistent antigen exposure favors their clonal expansion and accumulation of mutations, which further facilitate their activation. As a result, MB-like clonal precursors become trapped in an oscillatory state of semipermanent activation and phenotypic sway that facilitates ulterior transformation and accounts for the extranodal clinical presentation and biology of these tumors. In addition, we discuss diagnostic and therapeutic implications of a MB cell-of-origin for these lymphomas.

Age-Related Dynamics of Lung-Resident Memory CD8+ T Cells in the Age of COVID-19

Following respiratory viral infections or local immunizations, lung resident-memory T cells (T_RM) of the CD8 lineage provide protection against the same pathogen or related pathogens with cross-reactive T cell epitopes. Yet, it is now clear that, if homeostatic controls are lost following viral pneumonia, CD8 T_RM cells can mediate pulmonary pathology. We recently showed that the aging process can result in loss of homeostatic controls on CD8 T_RM cells in the respiratory tract. This may be germane to treatment modalities in both influenza and coronavirus disease 2019 (COVID-19) patients, particularly, the portion that present with symptoms linked to long-lasting lung dysfunction. Here, we review the developmental cues and functionalities of CD8 T_RM cells in viral pneumonia models with a particular focus on their capacity to mediate heterogeneous responses of immunity and pathology depending on immune status.

Transcriptome and IgH Repertoire Analyses Show That CD11chi B Cells Are a Distinct Population With Similarity to B Cells Arising in Autoimmunity and Infection

A distinct B cell population marked by elevated CD11c expression is found in patients with systemic lupus erythematosus (SLE). Cells with a similar phenotype have been described during chronic infection, but variable gating strategies and nomenclature have led to uncertainty of their relationship to each other. We isolated CD11c^hi cells from peripheral blood and characterized them using transcriptome and IgH repertoire analyses. Gene expression data revealed the CD11c^hi IgD⁺ and IgD^- subsets were highly similar to each other, but distinct from naive, memory, and plasma cell subsets. Although CD11c^hi B cells were enriched in some germinal center (GC) transcripts and expressed numerous negative regulators of B cell receptor (BCR) activation, they were distinct from GC B cells. Gene expression patterns from SLE CD11c^hi B cells were shared with other human diseases, but not with mouse age-associated B cells. IgH V-gene sequencing analysis showed IgD⁺ and IgD^- CD11c^hi B cells had somatic hypermutation and were clonally related to each other and to conventional memory and plasma cells. However, the IgH repertoires expressed by the different subsets suggested that defects in negative selection during GC transit could contribute to autoimmunity. The results portray a pervasive B cell population that accumulates during autoimmunity and chronic infection and is refractory to BCR signaling.

Memory B Cell Activation, Broad Anti-influenza Antibodies, and Bystander Activation Revealed by Single-Cell Transcriptomics

Antibody memory protects humans from many diseases. Protective antibody memory responses require activation of transcriptional programs, cell proliferation, and production of antigen-specific antibodies, but how these aspects of the response are coordinated is poorly understood. We profile the molecular and cellular features of the antibody response to influenza vaccination by integrating single-cell transcriptomics, longitudinal antibody repertoire sequencing, and antibody binding measurements. Single-cell transcriptional profiling reveals a program of memory B cell activation characterized by CD11c and T-bet expression associated with clonal expansion and differentiation toward effector function. Vaccination elicits an antibody clone, which rapidly acquired broad high-affinity hemagglutinin binding during affinity maturation. Unexpectedly, many antibody clones elicited by vaccination do not bind vaccine, demonstrating non-specific activation of bystander antibodies by influenza vaccination. These results offer insight into how molecular recognition, transcriptional programs, and clonal proliferation are coordinated in the human B cell repertoire during memory recall.

Antibody memory requires coordination of molecular recognition, gene expression programs, and clonal dynamics. Horns et al. study the human antibody memory response using single-cell and repertoire sequencing, revealing a transcriptional program of memory B cell activation, broadly binding anti-influenza antibodies, and widespread bystander activation of non-vaccine-binding antibodies after influenza vaccination.

B cell-specific XIST complex enforces X-inactivation and restrains atypical B cells

The long non-coding RNA (lncRNA) XIST establishes X chromosome inactivation (XCI) in female cells in early development and thereafter is thought to be largely dispensable. Here, we show XIST is continually required in adult human B cells to silence a subset of X-linked immune genes such as TLR7. XIST-dependent genes lack promoter DNA methylation and require continual XIST-dependent histone deacetylation. XIST RNA-directed proteomics and CRISPRi screen reveal distinctive somatic cell-type-specific XIST complexes and identify TRIM28 that mediates Pol II pausing at promoters of X-linked genes in B cells. Single-cell transcriptome data of female patients with either systemic lupus erythematosus or COVID-19 infection revealed XIST dysregulation, reflected by escape of XIST-dependent genes, in CD11c⁺ atypical memory B cells (ABCs). XIST inactivation with TLR7 agonism suffices to promote isotype-switched ABCs. These results indicate cell-type-specific diversification and function for lncRNA-protein complexes and suggest expanded roles for XIST in sex-differences in biology and medicine.

Deep Phenotyping of CD11c+ B Cells in Systemic Autoimmunity and Controls

Circulating CD11c⁺ B cells are a key phenomenon in certain types of autoimmunity but have also been described in the context of regular immune responses (i.e., infections, vaccination). Using mass cytometry to profile 46 different markers on individual immune cells, we systematically initially confirmed the presence of increased CD11c⁺ B cells in the blood of systemic lupus erythematosus (SLE) patients. Notably, significant differences in the expression of CD21, CD27, and CD38 became apparent between CD11c⁻ and CD11c⁺ B cells. We observed direct correlation of the frequency of CD21⁻CD27⁻ B cells and CD21⁻CD38⁻ B cells with CD11c⁺ B cells, which were most pronounced in SLE compared to primary Sjögren's syndrome patients (pSS) and healthy donors (HD). Thus, CD11c⁺ B cells resided mainly within memory subsets and were enriched in CD27⁻IgD⁻, CD21⁻CD27⁻, and CD21⁻CD38⁻ B cell phenotypes. CD11c⁺ B cells from all donor groups (SLE, pSS, and HD) showed enhanced CD69, Ki-67, CD45RO, CD45RA, and CD19 expression, whereas the membrane expression of CXCR5 and CD21 were diminished. Notably, SLE CD11c⁺ B cells showed enhanced expression of the checkpoint molecules CD86, PD1, PDL1, CD137, VISTA, and CTLA-4 compared to HD. The substantial increase of CD11c⁺ B cells with a CD21⁻ phenotype co-expressing distinct activation and checkpoint markers, points to a quantitative increased alternate (extrafollicular) B cell activation route possibly related to abnormal immune regulation as seen under the striking inflammatory conditions of SLE which shows a characteristic PD-1/PD-L1 upregulation.

Cellular and Humoral Immune Responses in Covid-19 and Immunotherapeutic Approaches

Coronavirus disease 2019 (Covid-19), caused by the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can range in severity from asymptomatic to severe/critical disease. SARS-CoV-2 uses angiotensin-converting enzyme 2 to infect cells leading to a strong inflammatory response, which is most profound in patients who progress to severe Covid-19. Recent studies have begun to unravel some of the differences in the innate and adaptive immune response to SARS-CoV-2 in patients with different degrees of disease severity. These studies have attributed the severe form of Covid-19 to a dysfunctional innate immune response, such as a delayed and/or deficient type I interferon response, coupled with an exaggerated and/or a dysfunctional adaptive immunity. Differences in T-cell (including CD4+ T-cells, CD8+ T-cells, T follicular helper cells, γδ-T-cells, and regulatory T-cells) and B-cell (transitional cells, double-negative 2 cells, antibody-secreting cells) responses have been identified in patients with severe disease compared to mild cases. Moreover, differences in the kinetic/titer of neutralizing antibody responses have been described in severe disease, which may be confounded by antibody-dependent enhancement. Importantly, the presence of preexisting autoantibodies against type I interferon has been described as a major cause of severe/critical disease. Additionally, priorVaccine and multiple vaccine exposure, trained innate immunity, cross-reactive immunity, and serological immune imprinting may all contribute towards disease severity and outcome. Several therapeutic and preventative approaches have been under intense investigations; these include vaccines (three of which have passed Phase 3 clinical trials), therapeutic antibodies, and immunosuppressants.

B cell depletion therapies in autoimmune disease: advances and mechanistic insights

In the past 15 years, B cells have been rediscovered to be not merely bystanders but rather active participants in autoimmune aetiology. This has been fuelled in part by the clinical success of B cell depletion therapies (BCDTs). Originally conceived as a method of eliminating cancerous B cells, BCDTs such as those targeting CD20, CD19 and BAFF are now used to treat autoimmune diseases, including systemic lupus erythematosus and multiple sclerosis. The use of BCDTs in autoimmune disease has led to some surprises. For example, although antibody-secreting plasma cells are thought to have a negative pathogenic role in autoimmune disease, BCDT, even when it controls the disease, has limited impact on these cells and on antibody levels. In this Review, we update our understanding of B cell biology, review the results of clinical trials using BCDT in autoimmune indications, discuss hypotheses for the mechanism of action of BCDT and speculate on evolving strategies for targeting B cells beyond depletion.

Ageing of Immune System and Response to a Live-Attenuated Herpes Zoster Vaccine in Lung Transplant Candidates

The mean age of lung transplant recipients has significantly increased in recent decades. Elderly recipients have a higher risk of developing herpes zoster (HZ), and they have in general a worse response to vaccination than younger persons do. We investigated the relationship between the humoral and cellular immune response to a live-attenuated HZ vaccine (Zostavax^®, Merck Sharp and Dohme) and the frequencies of T and B cell subsets, especially aged cell subsets (CD28−T cells and age associated B cells, ABCs). In total, 37 patients awaiting lung transplantation received one dose of Zostavax^®, and peripheral blood was collected before and within 6 months after vaccination. We observed a robust immune response after vaccination. The frequencies of CD28−T cells before vaccination had no impact on the subsequent immune response to HZ vaccination. However, a higher frequency of ABCs before vaccination correlated with a lower immune response especially regarding the cellular immune response. Cytomegalovirus seropositivity was associated with increased frequencies of CD28−T cells but not with frequencies of ABCs in the patients. In conclusion, increased levels of ABCs might disturb the cellular immune response to HZ vaccination, which could lower the efficacy of such vaccination in elderly transplant recipients.

Hyper-metabolic B cells in the spleens of old mice make antibodies with autoimmune specificities

BACKGROUND

Aging is associated with increased intrinsic B cell inflammation, decreased protective antibody responses and increased autoimmune antibody responses. The effects of aging on the metabolic phenotype of B cells and on the metabolic programs that lead to the secretion of protective versus autoimmune antibodies are not known.

METHODS

Splenic B cells and the major splenic B cell subsets, Follicular (FO) and Age-associated B cells (ABCs), were isolated from the spleens of young and old mice and left unstimulated. The RNA was collected to measure the expression of markers associated with intrinsic inflammation and autoimmune antibody production by qPCR. B cells and B cell subsets were also stimulated with CpG and supernatants collected after 7 days to measure autoimmune IgG secretion by ELISA. Metabolic measures (oxygen consumption rate, extracellular acidification rate and glucose uptake) were performed using a Seahorse XFp extracellular flux analyzer.

RESULTS

Results have identified the subset of ABCs, whose frequencies and numbers increase with age and represent the most pro-inflammatory B cell subset, as the cell type mainly if not exclusively responsible for the expression of inflammatory markers and for the secretion of autoimmune antibodies in the spleen of old mice. Hyper-inflammatory ABCs from old mice are also hyper-metabolic, as compared to those from young mice and to the subset of FO B cells, a feature needed not only to support their higher expression of RNA for inflammatory markers but also their higher autoimmune antibody secretion.

CONCLUSIONS

These results identify a relationship between intrinsic inflammation, metabolism and autoimmune B cells and suggest possible ways to understand cellular mechanisms that lead to the generation of pathogenic B cells, that are hyper-inflammatory and hyper-metabolic, and secrete IgG antibodies with autoimmune specificities.

The twilight of the immune system: The impact of immunosenescence in aging

Cellular senescence is a critical part of human anti-tumor defence; however, the accumulation of senescent cells with age underpins a wide range of pathologies. Senescent change in immune cells, or immunosenescence, has a wide range of physiological effects and is at least partially responsible for many diseases associated with aging. Immunosenescence underpins inflammaging, increased vulnerability to infectious disease with age, malignant change in the elderly, and auto-immunity. Understanding the effects and mechanisms of immunosenescence will improve disease outcomes and prevention in older adults, and generate new treatments for common illnesses. In this review we summarize the key changes occurring in immunosenescence across each facet of the immune system, and identify their clinical correlates.

Phenotypic and Functional Characterization of Double Negative B Cells in the Blood of Individuals With Obesity

We have previously shown that obesity is associated with increased secretion of IgG antibodies with anti-self-reactivity. In this paper, we confirm and extend our previous findings. We show that the plasma of individuals with obesity is enriched in autoimmune antibodies whose levels are positively associated with blood frequencies of the subset of Double Negative (DN) B cells, which is the most pro-inflammatory B cell subset. We also show that DN B cells, significantly increased in the blood of obese versus lean individuals, are characterized by higher expression of immune activation markers and of the transcription factor T-bet, both associated with autoimmunity. The removal of DN B cells from the peripheral B cell pool significantly decreases in vitro secretion of anti-self IgG antibodies. These results altogether confirm the crucial role of DN B cells in the secretion of anti-self IgG antibodies in individuals with obesity.

Inhibition of IRF5 hyperactivation protects from lupus onset and severity

The transcription factor IFN regulatory factor 5 (IRF5) is a central mediator of innate and adaptive immunity. Genetic variations within IRF5 are associated with a risk of systemic lupus erythematosus (SLE), and mice lacking Irf5 are protected from lupus onset and severity, but how IRF5 functions in the context of SLE disease progression remains unclear. Using the NZB/W F1 model of murine lupus, we show that murine IRF5 becomes hyperactivated before clinical onset. In patients with SLE, IRF5 hyperactivation correlated with dsDNA titers. To test whether IRF5 hyperactivation is a targetable function, we developed inhibitors that are cell permeable, nontoxic, and selectively bind to the inactive IRF5 monomer. Preclinical treatment of NZB/W F1 mice with an inhibitor attenuated lupus pathology by reducing serum antinuclear autoantibodies, dsDNA titers, and the number of circulating plasma cells, which alleviated kidney pathology and improved survival. Clinical treatment of MRL/lpr and pristane-induced lupus mice with an inhibitor led to significant reductions in dsDNA levels and improved survival. In ex vivo human studies, the inhibitor blocked SLE serum-induced IRF5 activation and reversed basal IRF5 hyperactivation in SLE immune cells. We believe this study provides the first in vivo clinical support for treating patients with SLE with an IRF5 inhibitor.

Hallmarks and detection techniques of cellular senescence and cellular ageing in immune cells

The ageing of the global population brings about unprecedented challenges. Chronic age-related diseases in an increasing number of people represent an enormous burden for health and social care. The immune system deteriorates during ageing and contributes to many of these age-associated diseases due to its pivotal role in pathogen clearance, tissue homeostasis and maintenance. Moreover, in order to develop treatments for COVID-19, we urgently need to acquire more knowledge about the aged immune system, as older adults are disproportionally and more severely affected. Changes with age lead to impaired responses to infections, malignancies and vaccination, and are accompanied by chronic, low-degree inflammation, which together is termed immunosenescence. However, the molecular and cellular mechanisms that underlie immunosenescence, termed immune cell senescence, are mostly unknown. Cellular senescence, characterised by an irreversible cell cycle arrest, is thought to be the cause of tissue and organismal ageing. Thus, better understanding of cellular senescence in immune populations at single-cell level may provide us with insight into how immune cell senescence develops over the life time of an individual. In this review, we will briefly introduce the phenotypic characterisation of aged innate and adaptive immune cells, which also contributes to overall immunosenescence, including subsets and function. Next, we will focus on the different hallmarks of cellular senescence and cellular ageing, and the detection techniques most suitable for immune cells. Applying these techniques will deepen our understanding of immune cell senescence and to discover potential druggable pathways, which can be modulated to reverse immune ageing.

Hallmarks of aging and immunosenescence: Connecting the dots

Aging is a natural physiological process that features various and variable challenges, associated with loss of homeostasis within the organism, often leading to negative consequences for health. Cellular senescence occurs when cells exhaust the capacity to renew themselves and their tissue environment as the cell cycle comes to a halt. This process is influenced by genetics, metabolism and extrinsic factors. Immunosenescence, the aging of the immune system, is a result of the aging process, but can also in turn act as a secondary inducer of senescence within other tissues. This review aims to summarize the current state of knowledge regarding hallmarks of aging in relation to immunosenescence, with a focus on aging-related imbalances in the medullary environment, as well as the components of the innate and adaptive immune responses. Aging within the immune system alters its functionality, and has consequences for the person's ability to fight infections, as well as for susceptibility to chronic diseases such as cancer and cardiovascular disease. The senescence-associated secretory phenotype is described, as well as the involvement of this phenomenon in the paracrine induction of senescence in otherwise healthy cells. Inflammaging is discussed in detail, along with the comorbidities associated with this process. A knowledge of these processes is required in order to consider possible targets for the application of senotherapeutic agents - interventions with the potential to modulate the senescence process, thus prolonging the healthy lifespan of the immune system and minimizing the secondary effects of immunosenescence.

Single-cell resolution landscape of equine peripheral blood mononuclear cells reveals diverse cell types including T-bet+ B cells

BACKGROUND

Traditional laboratory model organisms represent a small fraction of the diversity of multicellular life, and findings in any given experimental model often do not translate to other species. Immunology research in non-traditional model organisms can be advantageous or even necessary, such as when studying host-pathogen interactions. However, such research presents multiple challenges, many stemming from an incomplete understanding of potentially species-specific immune cell types, frequencies, and phenotypes. Identifying and characterizing immune cells in such organisms is frequently limited by the availability of species-reactive immunophenotyping reagents for flow cytometry, and insufficient prior knowledge of cell type-defining markers.

RESULTS

Here, we demonstrate the utility of single-cell RNA sequencing (scRNA-Seq) to characterize immune cells for which traditional experimental tools are limited. Specifically, we used scRNA-Seq to comprehensively define the cellular diversity of equine peripheral blood mononuclear cells (PBMC) from healthy horses across different breeds, ages, and sexes. We identified 30 cell type clusters partitioned into five major populations: monocytes/dendritic cells, B cells, CD3+PRF1+ lymphocytes, CD3+PRF1- lymphocytes, and basophils. Comparative analyses revealed many cell populations analogous to human PBMC, including transcriptionally heterogeneous monocytes and distinct dendritic cell subsets (cDC1, cDC2, plasmacytoid DC). Remarkably, we found that a majority of the equine peripheral B cell compartment is comprised of T-bet+ B cells, an immune cell subpopulation typically associated with chronic infection and inflammation in human and mouse.

CONCLUSIONS

Taken together, our results demonstrate the potential of scRNA-Seq for cellular analyses in non-traditional model organisms and form the basis for an immune cell atlas of horse peripheral blood.

B and T Cell Immunity in Tissues and Across the Ages

B and T cells are key components of the adaptive immune system and coordinate multiple facets of immunity including responses to infection, vaccines, allergens, and the environment. In humans, B- and T-cell immunity has been determined using primarily peripheral blood specimens. Conversely, human tissues have scarcely been studied but they host multiple adaptive immune cells capable of mounting immune responses to pathogens and participate in tissue homeostasis. Mucosal tissues, such as the intestines and respiratory track, are constantly bombarded by foreign antigens and contain tissue-resident memory T (T_RM) cells that exhibit superior protective capacity to pathogens. Also, tissue-resident memory B (B_RM) cells have been identified in mice but whether humans have a similar population remains to be confirmed. Moreover, the immune system evolves throughout the lifespan of humans and undergoes multiple changes in its immunobiology. Recent studies have shown that age-related changes in tissues are not necessarily reflected in peripheral blood specimens, highlighting the importance of tissue localization and subset delineation as essential determinants of functional B and T cells at different life stages. This review describes our current knowledge of the main B- and T-cell subsets in peripheral blood and tissues across age groups.

B cell-specific XIST complex enforces X-inactivation and restrains atypical B cells

The long noncoding RNA (lncRNA) XIST establishes X chromosome inactivation (XCI) in female cells in early development and thereafter is thought to be largely dispensable. Here we show XIST is continually required in adult human B cells to silence a subset of X-linked immune genes such as TLR7 . XIST-dependent genes lack promoter DNA methylation and require continual XIST-dependent histone deacetylation. XIST RNA-directed proteomics and CRISPRi screen reveal distinctive somatic cell-specific XIST complexes, and identify TRIM28 that mediates Pol II pausing at promoters of X-linked genes in B cells. XIST dysregylation, reflected by escape of XIST-dependent genes, occurs in CD11c+ atypical memory B cells across single-cell transcriptome data in patients with female-biased autoimmunity and COVID-19 infection. XIST inactivation with TLR7 agonism suffices to promote isotype-switched atypical B cells. These results suggest cell-type-specific diversification of lncRNA-protein complexes increase lncRNA functionalities, and expand roles for XIST in sex-differences in biology and medicine.

HIGHLIGHTS

XIST prevents escape of genes with DNA hypomethylated promoters in B cells.XIST maintains X-inactivation through continuous deacetylation of H3K27ac.XIST ChIRP-MS and allelic CRISPRi screen reveal a B cell-specific XIST cofactor TRIM28.XIST loss and TLR7 stimulation promotes CD11c+ atypical B cell formation.

Type 1 helper T cells generate CXCL9/10-producing T-bet+ effector B cells potentially involved in the pathogenesis of rheumatoid arthritis

Efficacy of B-cell depletion therapy highlights the antibody-independent effector functions of B cells in rheumatoid arthritis (RA). Given type 1 helper T (Th1) cells abundant in synovial fluid (SF) of RA, we have determined whether Th1 cells could generate novel effector B cells. Microarray and qPCR analysis identified CXCL9/10 transcripts as highly expressed genes upon BCR/CD40/IFN-γ stimulation. Activated Th1 cells promoted the generation of CXCL9/10-producing T-bet⁺ B cells. Expression of CXCL9/10 was most pronounced in CXCR3⁺ switched memory B cells. Compared with peripheral blood, SFRA enriched highly activated Th1 cells that coexisted with abundant CXCL9/10-producing T-bet⁺ B cells. Intriguingly, anti-IFN-γ antibody and JAK inhibitors significantly abrogated the generation of CXCL9/10-producing T-bet⁺ B cells. B cell derived CXCL9/10 significantly facilitated the migration of CD4⁺ T cells. These findings suggest that Th1 cells generate the novel CXCL9/10-producing T-bet⁺ effector B cells that could be an ideal pathogenic B cell target for RA therapy.

Toll-like receptor signalling in B cells during systemic lupus erythematosus

B lymphocytes have a central role in autoimmune diseases, which are often defined by specific autoantibody patterns and feature a loss of B cell tolerance. A prototypic disease associated with B cell hyperactivity is systemic lupus erythematosus (SLE). In patients with SLE, the loss of B cell tolerance to autoantigens is controlled in a cell-intrinsic manner by Toll-like receptors (TLRs), which sense nucleic acids in endosomes. TLR7 drives the extrafollicular B cell response and the germinal centre reaction that are involved in autoantibody production and disease pathogenesis. Surprisingly, TLR9 seems to protect against SLE, even though it is required for the production of autoantibodies recognizing double-stranded DNA-associated antigens, which are abundant in SLE and are a hallmark of this disease. The protective function of TLR9 is at least partly mediated by its capacity to limit the stimulatory activity of TLR7. The roles of TLR7 and TLR9 in the effector function of B cells in lupus-like disease and in patients with SLE, and the unique features of TLR signalling in B cells, suggest that targeting TLR signalling in SLE might be therapeutically beneficial.

Loss of B cell tolerance to autoantigens in systemic lupus erythematosus (SLE) is driven by TLR7, whereas TLR9 appears to protect against SLE by limiting the stimulatory activity of TLR7. The unique features of Toll-like receptor signalling in B cells implicate it as a therapeutic target in SLE.

Intrinsic TLR7 and TLR9 signalling in B cells plays an important role in the development and pathogenesis of systemic lupus erythematosus (SLE).

In patients with SLE, effector plasma cells are generated via the extrafollicular response and via the formation of spontaneous germinal centres.

TLR7 plays key roles in the extrafollicular response and the response mediated by germinal centres.

Some plasma cells produce IL-10 and can have protective roles in lupus-like disease.

The B cell response to both protein and nucleic acid antigens displayed on apoptotic cells are dependent on endosomal pattern recognition receptors

In systemic autoimmune diseases such as systemic lupus erythematosus (SLE), B cell tolerance is lost and there is a production of autoantibodies that drive pathology. The specificities of these antibodies are towards a wide range of autoantigens including proteins such as serum factors including cytokines as well as towards nucleic acids and modified glycolipids. It is known that endosomal pattern recognition receptors are involved in specific responses but if they drive specificity towards a specific group of autoantigens is not known. Here, we used syngeneic apoptotic cells alone to break B cell tolerance and investigated the antibody response in Unc93b1 mutant mice that lack signalling from the TLR3, TLR7 and TLR9 receptors. We found that specific B cell responses known from patients with SLE including antibodies towards Ro-52/60, La, cardiolipin as well as DNA were all significantly lower in the knockout mice. Thus, we found that endosomal TLR receptors were involved in break of tolerance and drive B cell responses for protein, nucleic acid and modified lipid antigens. This pinpoints these receptors as key drivers for the full range of antibody driven pathology in SLE and suggests that targeting of endosomal TLR driven responses will quench all B cell driven autoreactivity.

Understanding immunosenescence and its impact on vaccination of older adults

Older adults are more susceptible to viral and bacterial infection, and experience higher incidence and severity of infectious diseases. Although vaccination is the most logical solution in preventing infectious diseases, primary vaccine responses in individuals aged ≥65 years-old fail to generate complete protection. This is presumably attributed to immunosenescence, a term that describes functional differences associated with the immune system and natural age advancement. Both the innate and adaptive immune systems experience age-related impairments that contribute to insufficient protection following vaccination. This review addresses current knowledge of age-related changes that affect vaccine responsiveness; including the deficits in innate cell functions, dampened humoral and cell-mediated immune responses, current vaccination schedules for older adults, and concludes with potential strategies for improving vaccine efficacy specifically for this age group. Due to an age-related decline in immunity and poor vaccine responses, infectious diseases remain a burden among the aged population.

Aging induces B cell defects and decreased antibody responses to influenza infection and vaccination

Background

Aging is characterized by a progressive decline in the capacity of the immune system to fight influenza virus infection and to respond to vaccination. Among the several factors involved, in addition to increased frailty and high-risk conditions, the age-associated decrease in cellular and humoral immune responses plays a relevant role. This is in large part due to inflammaging, the chronic low-grade inflammatory status of the elderly, associated with intrinsic inflammation of the immune cells and decreased immune function.

Results

Aging is usually associated with reduced influenza virus-specific and influenza vaccine-specific antibody responses but some elderly individuals with higher pre-exposure antibody titers, due to a previous infection or vaccination, have less probability to get infected. Examples of this exception are the elderly individuals infected during the 2009 pandemic season who made antibodies with broader epitope recognition and higher avidity than those made by younger individuals. Several studies have allowed the identification of B cell intrinsic defects accounting for sub-optimal antibody responses of elderly individuals. These defects include 1) reduced class switch recombination, responsible for the generation of a secondary response of class switched antibodies, 2) reduced de novo somatic hypermutation of the antibody variable region, 3) reduced binding and neutralization capacity, as well as binding specificity, of the secreted antibodies, 4) increased epigenetic modifications that are associated with lower antibody responses, 5) increased frequencies of inflammatory B cell subsets, and 6) shorter telomeres.

Conclusions

Although influenza vaccination represents the most effective way to prevent influenza infection, vaccines with greater immunogenicity are needed to improve the response of elderly individuals. Recent advances in technology have made possible a broad approach to better understand the age-associated changes in immune cells, needed to design tailored vaccines and effective therapeutic strategies that will be able to improve the immune response of vulnerable individuals.

Age-associated B Cells Appear in Patients with Granulomatous Lung Diseases

Rationale: A subpopulation of B cells (age-associated B cells [ABCs]) is increased in mice and humans with infections or autoimmune diseases. Because depletion of these cells might be valuable in patients with certain lung diseases, the goal was to find out if ABC-like cells were at elevated levels in such patients.Objectives: To measure ABC-like cell percentages in patients with lung granulomatous diseases.Methods: Peripheral blood and BAL cells from patients with sarcoidosis, beryllium sensitivity, or hypersensitivity pneumonitis and healthy subjects were analyzed for the percentage of B cells that were ABC-like, defined by expression of CD11c, low levels of CD21, FcRL 1-5 (Fc receptor-like protein 1-5) expression, and, in some cases, T-bet.Measurements and Main Results: ABC-like cells in blood were at low percentages in healthy subjects and higher percentages in patients with sarcoidosis as well as at high percentages among BAL cells of patients with sarcoidosis, beryllium disease, and hypersensitivity pneumonitis. Treatment of patients with sarcoidosis led to reduced percentages of ABC-like cells in blood.Conclusions: Increased levels of ABC-like cells in patients with sarcoidosis may be useful in diagnosis. The increase in percentage of ABC-like cells in patients with lung granulomatous diseases and decrease in treated patients suggests that depletion of these cells may be valuable.

Senescence in Pulmonary Fibrosis: Between Aging and Exposure

To date, chronic pulmonary pathologies represent the third leading cause of death in the elderly population. Evidence-based projections suggest that >65 (years old) individuals will account for approximately a quarter of the world population before the turn of the century. Genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication, are described as the nine “hallmarks” that govern cellular fitness. Any deviation from the normal pattern initiates a complex cascade of events culminating to a disease state. This blueprint, originally employed to describe aberrant changes in cancer cells, can be also used to describe aging and fibrosis. Pulmonary fibrosis (PF) is the result of a progressive decline in injury resolution processes stemming from endogenous (physiological decline or somatic mutations) or exogenous stress. Environmental, dietary or occupational exposure accelerates the pathogenesis of a senescent phenotype based on (1) window of exposure; (2) dose, duration, recurrence; and (3) cells type being targeted. As the lung ages, the threshold to generate an irreversibly senescent phenotype is lowered. However, we do not have sufficient knowledge to make accurate predictions. In this review, we provide an assessment of the literature that interrogates lung epithelial, mesenchymal, and immune senescence at the intersection of aging, environmental exposure and pulmonary fibrosis.

Activation of group 2 innate lymphoid cells alleviates aging-associated cognitive decline

Increasing evidence has challenged the traditional view about the immune privilege of the brain, but the precise roles of immune cells in regulating brain physiology and function remain poorly understood. Here, we report that tissue-resident group 2 innate lymphoid cells (ILC2) accumulate in the choroid plexus of aged brains. ILC2 in the aged brain are long-lived, are relatively resistant to cellular senescence and exhaustion, and are capable of switching between cell cycle dormancy and proliferation. They are functionally quiescent at homeostasis but can be activated by IL-33 to produce large amounts of type 2 cytokines and other effector molecules in vitro and in vivo. Intracerebroventricular transfer of activated ILC2 revitalized the aged brain and enhanced the cognitive function of aged mice. Administration of IL-5, a major ILC2 product, was sufficient to repress aging-associated neuroinflammation and alleviate aging-associated cognitive decline. Targeting ILC2 in the aged brain may provide new avenues to combat aging-associated neurodegenerative disorders.

Potential functions of atypical memory B cells in Plasmodium-exposed individuals

Naturally acquired iummunity against clinical malaria is slow to develop, taking years of repeated exposure to parasites to acquire sufficiently broad and potent antibody responses. Increasing evidence suggests that Plasmodium infection and the resulting immune stimulation contribute to changes in the B cell compartment. In particular, accumulation of atypical memory B cells (atMBCs) is common in Plasmodium-exposed individuals. Similarities to B cell subsets present in other acute and chronic disease settings have provided insight into the development and potential function of these cells; however, their contribution to protection against malaria is still poorly understood. Here, we discuss recent findings that have increased our understanding of atMBCs and outline outstanding questions related to their function and development in the protective immune response to malaria.

I mmunosenescence and Inflammaging: Risk Factors of Severe COVID-19 in Older People

Old individuals are more susceptible to various infections due to immunological changes that occur during the aging process. These changes named collectively as "immunosenescence" include decreases in both the innate and adaptive immune responses in addition to the exacerbated production of inflammatory cytokines. This scenario of immunological dysfunction and its relationship with disease development in older people has been widely studied, especially in infections that can be fatal, such as influenza and, more recently, COVID-19. In the current scenario of SARS-CoV-2 infection, many mechanisms of disease pathogenesis in old individuals have been proposed. To better understand the dynamics of COVID-19 in this group, aspects related to immunological senescence must be well elucidated. In this article, we discuss the main mechanisms involved in immunosenescence and their possible correlations with the susceptibility of individuals of advanced age to SARS-CoV-2 infection and the more severe conditions of the disease.

Taurine Metabolism Aggravates the Progression of Lupus by Promoting the Function of Plasmacytoid Dendritic Cells

OBJECTIVE

Type I interferons (IFNs) are critical in the development of systemic lupus erythematosus (SLE). Metabolic abnormalities cause dysregulation of multiple immune cells, but the metabolic regulation of type I IFN production is not well clarified in SLE. We undertook this study to define amino acid metabolism features in SLE and to explore the function of disease-relevant metabolites in the control of plasmacytoid dendritic cell (pDC)-mediated type I IFN production and the progression of SLE.

METHODS

Metabolomic profiling of the serum from SLE patients and healthy controls was performed by mass spectrometry. The effects of SLE-related metabolites on type I IFN production were explored in human and mouse pDCs. The reactive oxygen species (ROS) levels of pDCs from wild-type and Ncf1^-/- mice were measured by flow cytometry. Mechanisms were investigated by RNA sequencing and immunoblotting. In vivo effects of SLE-relevant metabolites were systemically analyzed in B6.Cg-Sle1^NZM2410/Aeg Yaa/DcrJ mice.

RESULTS

Taurine was higher in the serum from SLE patients compared to healthy controls (P < 0.001) and rheumatoid arthritis patients (P < 0.001). Taurine content was positively correlated with disease activity and the expression of IFN signature genes. The addition of taurine facilitated IFN regulatory factor 7 phosphorylation and enhanced type I IFN production by reducing the ROS levels in pDCs in a neutrophil cytosolic factor 1-dependent manner. Taurine supplementation promoted expression of type I IFN-induced genes, activated lymphocytes, and increased autoantibodies and proteinuria, leading to more serious nephritis.

CONCLUSION

Taurine metabolism is involved in the development of SLE by enhancing pDC-mediated type I IFN production. Targeted inhibition of taurine or implementation of a taurine-restricted diet has therapeutic potential in SLE.

Selective DNA Demethylation Accompanies T Cell Homeostatic Proliferation and Gene Regulation in Lupus-Prone lpr Mice

Systemic lupus erythematosus (SLE) is characterized by increased DNA demethylation in T cells, although it is unclear whether this occurs primarily in a subset of SLE T cells. The process driving the DNA demethylation and the consequences on overall gene expression are also poorly understood and whether this represents a secondary consequence of SLE or a primary contributing factor. Lupus-prone lpr mice accumulate large numbers of T cells with age because of a mutation in Fas (CD95). The accumulating T cells include an unusual population of CD4-CD8-TCR-αβ+ (DN) T cells that arise from CD8+ precursors and are also found in human SLE. We have previously observed that T cell accumulation in lpr mice is due to dysregulation of T cell homeostatic proliferation, which parallels an increased expression of numerous genes in the DN subset, including several proinflammatory molecules and checkpoint blockers. We thus determined the DNA methylome in lpr DN T cells compared with their CD8+ precursors. Our findings show that DN T cells manifest discrete sites of extensive demethylation throughout the genome, and these sites correspond to the location of a large proportion of the upregulated genes. Thus, dysregulated homeostatic proliferation in lpr mice and consequent epigenetic alterations may be a contributing factor to lupus pathogenesis.

The Antigen Presenting Potential of CD21low B Cells

Human CD21^low B cells are expanded in autoimmune (AI) diseases and display a unique phenotype with high expression of co-stimulatory molecules, compatible with a potential role as antigen-presenting cells (APCs). Thus, we addressed the co-stimulatory capacity of naïve-like, IgM-memory, switched memory and CD27^negIgD^neg memory CD21^low B cells in allogenic co-cultures with CD4 T cells. CD21^low B cells of patients with AI disorders expressed high levels of not only CD86, CD80, and HLA-DR (memory B cells) but also PD-L1 ex vivo and efficiently co-stimulated CD4 T cells of healthy donors (HD), as measured by upregulation of CD25, CD69, inducible co-stimulator (ICOS), and programmed cell death protein 1 (PD-1) and induction of cytokines. While the co-stimulatory capacity of the different CD21^low B-cell populations was over all comparable to CD21^pos counterparts of patients and HD, especially switched memory CD21^low B cells lacked the increased capacity of CD21^pos switched memory B-cells to induce high expression of ICOS, IL-2, IL-10, and IFN-γ. Acknowledging the limitation of the in vitro setting, CD21^low B cells do not seem to preferentially support a specific T_h effector response. In summary, our data implies that CD21^low B cells of patients with AI diseases can become competent APCs and may, when enriched for autoreactive B-cell receptors (BCR), potentially contribute to AI reactions as cognate interaction partners of autoreactive T cells at sites of inflammation.

Bullous Pemphigoid: Trigger and Predisposing Factors

Bullous pemphigoid (BP) is the most frequent autoimmune subepidermal blistering disease provoked by autoantibodies directed against two hemidesmosomal proteins: BP180 and BP230. Its pathogenesis depends on the interaction between predisposing factors, such as human leukocyte antigen (HLA) genes, comorbidities, aging, and trigger factors. Several trigger factors, such as drugs, thermal or electrical burns, surgical procedures, trauma, ultraviolet irradiation, radiotherapy, chemical preparations, transplants, and infections may induce or exacerbate BP disease. Identification of predisposing and trigger factors can increase the understanding of BP pathogenesis. Furthermore, an accurate anamnesis focused on the recognition of a possible trigger factor can improve prognosis by promptly removing it.

B Cell αv Integrins Regulate TLR-Driven Autoimmunity

Systemic lupus erythematosus (SLE) is defined by loss of B cell tolerance, resulting in production of autoantibodies against nucleic acids and other cellular Ags. Aberrant activation of TLRs by self-derived RNA and DNA is strongly associated with SLE in patients and in mouse models, but the mechanism by which TLR signaling to self-ligands is regulated remains poorly understood. In this study, we show that αv integrin plays a critical role in regulating B cell TLR signaling to self-antigens in mice. We show that deletion of αv from B cells accelerates autoantibody production and autoimmune kidney disease in the Tlr7.1 transgenic mouse model of SLE. Increased autoimmunity was associated with specific expansion of transitional B cells, extrafollicular IgG2c-producing plasma cells, and activation of CD4 and CD8 T cells. Our data show that αv-mediated regulation of TLR signaling in B cells is critical for preventing autoimmunity and indicate that loss of αv promotes escape from tolerance. Thus, we identify a new regulatory pathway in autoimmunity and elucidate upstream signals that adjust B cell activation to prevent development of autoimmunity in a mouse model.

Immunosenescence is both functional/adaptive and dysfunctional/maladaptive

Alterations in the immune system with aging are considered to underlie many age-related diseases. However, many elderly individuals remain healthy until even a very advanced age. There is also an increase in numbers of centenarians and their apparent fitness. We should therefore change our unilaterally detrimental consideration of age-related immune changes. Recent data taking into consideration the immunobiography concept may allow for meaningful distinctions among various aging trajectories. This implies that the aging immune system has a homeodynamic characteristic balanced between adaptive and maladaptive aspects. The survival and health of an individual depends from the equilibrium of this balance. In this article, we highlight which parts of the aging of the immune system may be considered adaptive in contrast to those that may be maladaptive.

Age-Associated B Cells (ABCs) in the Prognosis, Diagnosis and Therapy of Systemic Lupus Erythematosus (SLE)

The term “age-associated B cells” (ABCs) refers to a heterogeneous B cell subset (CD19⁺,CD21⁻, CD11c⁺,T-bet⁺) which is expanded in the elderly, but also accumulates prematurely in patients with autoimmune disorders and/or infectious diseases. In healthy individuals, ABCs represent a low prevalence population that positively impacts immunosenescence. In autoimmunity and infections though, ABCs expand dramatically and produce high titers of antibodies, thus playing a role in the regulation of humoral responses. Despite the fact that these observations were made on both mice and humans, the functional features of ABCs and their exact role in human health and disease are still elusive. This review focuses on ABC and ABC-like sub-populations found in Systemic Lupus Erythematosus (SLE) patients (such as the double negative 2;DN2 population: CD19⁺,IgD⁻,CD27⁻, CXCR5⁻,T-bet⁺) and broaches the subject of their potential use as prognostic and/or diagnostic markers. The identification of novel biomarkers, via correlating the cell populations with the clinical profile of the patients, should enable better patient stratification and monitoring. Moreover, the necessity and importance of elucidating the role of transcription factor T-bet (TBX21) in the pathogenesis of human autoimmunity are addressed. T-bet, whose expression is upregulated in both mouse and human ABCs, is considered to play a major role in various aspects of autoimmunity, such as the production of autoreactive IgG, the enhanced antigen presentation to T cells and also the formation of spontaneous germinal centres (GC). Shedding light to its role in human disease, in conjunction with the characterisation of genes and pathways associated with the transcription factor itself, may lead to the discovery of novel druggable targets.

Activated Human Memory B Lymphocytes Use CR4 (CD11c/CD18) for Adhesion, Migration, and Proliferation

Complement receptors CR3 (CD11b/CD18) and CR4 (CD11c/CD18) of myeloid cells are known for long to participate in actin linked functions like phagocytosis, adhesion, and migration. The expression and role of these two β₂-integrins however, in human B lymphocytes have only scarcely been studied so far, although it has been shown recently that CD11c⁺ B cells are mainly memory cells. In our systematic study we investigated B cells isolated from tonsils and peripheral blood of healthy donors. We found, that while only 5% of resting tonsillar B cells expressed CD11c, their number increased up to 26% after 3 days of BCR stimulation. Lower, but still remarkable percentage of B lymphocytes were positive for CD11c after stimulation via TLR9 alone or via TLR9 and BCR simultaneously. At the same time, we detected no significant expression of CD11b on resting or activated tonsillar B cells. Blood B lymphocytes showed a similar expression pattern of both β₂-integrins. We demonstrated that CD11c molecules appearing on the surface of B cells are newly synthesized, reaching the number of 9,500 per activated B cell. We found that CR4 expressing B cells belong to the memory pool and the increase of CD11c expression on tonsillar B cells upon BCR mediated activation occurs parallel with class switching. Analysis of the function of CD11c revealed, that this β₂-integrin contributes to the adhesion and migration of activated B lymphocytes. We also demonstrated that the CR4 mediated adhesion promotes the proliferation of the BCR activated cells. Our studies are the first to demonstrate that CD11c expressed on BCR-activated human B cells are not only passive markers but functional drivers of memory B cell responses.