NADPH oxidase exerts a B cell-intrinsic contribution to lupus risk by modulating endosomal TLR signals

α-Ketoglutarate alleviates the pathogenesis of lupus and inhibits the activation and differentiation of B cells by promoting the expression of CD39

The abnormal activation and differentiation of B cells play an important role in the pathogenesis of autoimmune diseases, including systemic lupus erythematosus (SLE). Alpha-ketoglutarate (α-KG), a key metabolite in the tricarboxylic acid cycle, has been shown to be involved in the pathogenesis of many diseases by regulating the immune response. However, the role of α-KG in the pathogenesis of SLE, as well as the activation and differentiation of B cells, remains unclear. In this study, we used organic acid-targeted metabolomics to analyze the changes in the levels of 100 organic acids in the serum of SLE patients and healthy controls, and found a significant increase in the α-KG level in SLE patients compared to that in healthy controls. Notably, α-KG significantly could inhibit the activation and differentiation of B cells and alleviate disease progression in lupus-prone mice. Mechanistically, RNA-seq revealed that α-KG upregulated the expression of ENTPD1, which encodes an important immune checkpoint molecule CD39; B-cell-specific loss of ENTPD1 could significantly promote the Toll-like receptors-mediated activation and differentiation of B cells and aggravate the disease conditions of lupus-prone mice. The findings of our study demonstrate that α-KG alleviates the pathogenesis of lupus and inhibits the activation and differentiation of B cells by increasing the expression of CD39. Our findings laid a theoretical foundation for understanding the pathogenesis of SLE. Based on our study, α-KG might be further examined as a drug for the effective treatment of SLE.

What's atypical about human B cells after allogeneic stem cell transplantation?

Atypical B cells or age-associated B cells represent an alternative lineage of memory B cells. Emerging evidence suggests that context influences the apparent functional heterogeneity of age-associated B cells. While data support a protective role for age-associated B cells in the setting of infection, multiple other studies suggest that these cells play a pathogenic role in the setting of autoimmunity. After treatment with allogeneic hematopoietic stem cell transplantation, the memory B-cell compartment is altered in patients who develop an autoimmune-like syndrome called chronic graft-versus-host disease. Patients with chronic graft-versus-host disease have significantly increased proportions of CD11c+ age-associated B cells within the peripheral compartment that develop under constant exposure to host alloantigens and persist under conditions when B-cell tolerance is not achieved. Herein, we review what is currently known about the molecular alterations in the heterogeneous memory B-cell compartment of hematopoietic stem cell transplantation patients, especially patients with chronic graft-versus-host disease who have developed autoimmune manifestations. In this mini-review, we summarize intrinsic factors in age-associated B cells found in autoimmune states that likely influence their extrafollicular localization, differentiation potential into autoantibody-secreting cells, and function. We highlight lessons from B-cell studies in chronic graft-versus-host disease to provide unique insights into the molecular underpinnings of the diverse functions of age-associated B cells.

The Role of NADPH Oxidase 2 in Leukocytes

NADPH oxidase (NOX) family members are major resources of intracellular reactive oxygen species (ROS). In the immune system, ROS derived from phagocytic NOX (NOX2) participate in both pathogen clearance and signaling transduction. The role of NOX2 in neutrophils and macrophages has been well studied as mutations in NOX2 subunits cause chronic granulomas disease (CGD). NOX2 is expressed across a wide range of immune cells and recent reports have demonstrated that NOX2-derived ROS play important roles in other immune cells during an immune response. In this review, we summarize current knowledge of functions of NADPH oxidase 2 in each subset of leukocytes, as well as associations of NOX2 deficiency with diseases associated specifically with autoimmunity and immune deficiency. We also discuss important knowledge gaps as well as potential future directions for NOX2 research.

Human hypofunctional NCF1 variants promote pulmonary fibrosis in the bleomycin-induced mouse model and patients with systemic sclerosis via expansion of SPP1+ monocytes-derived macrophages

OBJECTIVE

We assessed the role of a systemic lupus erythematosus causal hypofunctional variant, neutrophil cytosolic factor 1 (NCF1)-p.Arg90His (p.R90H) substitution, in systemic sclerosis (SSc).

METHODS

Association of NCF1-H90 with SSc was performed in case-control cohorts, bleomycin (BLM)-treated Ncf1-R90 C57BL/6 wildtype and Ncf1-H90 knock-in (KI) littermates. Peripheral blood mononuclear cell (PBMC) subsets were analysed by cytometry by time-of-flight.

RESULTS

The NCF1-H90 allele is associated with risk for diffuse cutaneous SSc (dcSSc) in Chinese and European Americans, and lung fibrosis in Chinese patients with SSc (OR=2.09, p=7.96E-10). Low copy number of NCF1 associated with lung fibrosis in European Americans (OR=4.33, p=2.60E-2). BLM-treated KI mice demonstrated increased pulmonary fibrosis, exhibiting activated type I interferon signature, elevated Spp1, Ccl2, Arg1, Timp1 and Il6 expression, enriched macrophage scores in lung tissues. In a longitudinal observation cohort, homozygous H90 patients with SSc at baseline had increased anti-nuclear antibody titres, anti-topoisomerase antibody seropositivity and anti-centromere antibody seronegativity, increased incidence of lung fibrosis and Gender-Age-lung Physiology index, elevated modified Rodnan Skin Score (mRSS) and elevated plasma osteopontin (OPN, SPP1), CCL2, ARG1, TIMP-1 and IL-6. These H90 patients with SSc sustained elevated mRSS during follow-up years with decreased survival. The 0, 1 and 2 copies of H90 carriage in SSc PBMCs exhibited dose-dependent increases in profibrotic CD14+CD68+CD11b+Tim3+monocytes. Elevated OPN, CCL2 and ARG1 in CD68+CD11b+monocyte-derived macrophages from H90 patients were decreased after co-culturing with anti-CCL2 antibody.

CONCLUSION

Low NCF1 activity increases the risk for the development of dcSSc and lung fibrosis via expanding profibrotic SPP1+MoMs in a CCL2-dependent manner, contributing to the severity of lung fibrosis in both BLM-treated mice and patients with SSc.

B cell adapter for PI 3-kinase (BCAP) coordinates antigen internalization and trafficking through the B cell receptor

B cell adapter for PI 3-kinase (BCAP) is an adaptor molecule associated with signaling through multiple immune receptors, including the B cell receptor (BCR). However, B cell-intrinsic role of BCAP in antibody responses is unclear. We investigated the role of BCAP in B cell response to viral particles and found a previously unidentified mechanism by which BCAP regulates antigen-specific responses. B cell-specific deletion of BCAP in mice leads to decreases in antigen-specific responses through defects in BCR-antigen endocytosis. BCAP is necessary to orchestrate actin reorganization around the antigen for efficient endocytosis through BCR and intracellular processing of antigens. Therefore, loss of BCAP from B cells leads to defects in antigen endocytosis, hampering the propagation of antigen-derived signals and decreasing the ability of B cells to present antigens to T cells. Thus, our study clarifies how BCAP regulates B cell responses to complex antigens and elucidates that antigen positioning inside B cells determines different B cell activation outcomes.

NADPH oxidase in B cells and macrophages protects against murine lupus by regulation of TLR7

Loss of NADPH oxidase (NOX2) exacerbates systemic lupus erythematosus (SLE) in mice and humans, but the mechanisms underlying this effect remain unclear. To identify the cell lineages in which NOX2 deficiency drives SLE, we employed conditional KO and chimeric approaches to delete Cybb in several hematopoietic cell lineages of MRL.Faslpr SLE-prone mice. Deletion of Cybb in macrophages/monocytes exacerbated SLE nephritis, though not to the degree observed in the Cybb global KOs. Unexpectedly, the absence of Cybb in B cells resulted in profound glomerulonephritis and interstitial nephritis, rivaling that seen with global deletion. Furthermore, we identified that NOX2 is a key regulator of TLR7, a driver of SLE pathology, both globally and specifically in B cells. This is mediated in part through suppression of TLR7-mediated NF-κB signaling in B cells. Thus, NOX2's immunomodulatory effect in SLE is orchestrated not only by its function in the myeloid compartment, but through a pivotal role in B cells by selectively inhibiting TLR7 signaling.