Noncanonical B Cells: Characteristics of Uncharacteristic B Cells

Integrated analyses uncover new features of atypical memory B cells and novel targets for intervention

BACKGROUND

Atypical memory B (AMB) is a novel subset of B lymphocytes, but its immune features and pathogenetic roles in systemic rheumatic diseases are still largely elusive. This study aimed to characterize transcriptomic features, immune phenotypes and potential signaling pathways of AMB, and also to confirm its alternations in systemic rheumatic diseases via combined transcriptome analyses.

METHOD

B cell subsets and their transcriptomic signatures were identified via analyses of single cell RNA-sequencing (scRNA-seq) data. Functional characterization of AMB was performed with bioinformatics and CyTOF-based phenotyping. Alternation of AMB in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and Sjögren's syndrome (SjS) was evaluated via bioinformatic approaches.

RESULT

A total of 11 B cell subsets including AMB were identified through scRNA-seq transcriptome analyses. Both transcriptome analyses and CyTOF-based immune phenotyping confirmed that AMB had increased levels of TBX21 (T-bet), ITGAX (CD11c), CD19, CD20 and CXCR3 (P < 0.05), and it had decreased expressions of CD27, CD38, CXCR4, CXCR5 and CD62L (P < 0.05). More than 50 % of T-bet+ B cells did not express CD11c, and more than 30 % expressed CD27. AMB was characterized by activated mTORC1 signaling and increased p-P38 level (P < 0.05). AMB transcriptional signature was significantly enriched in the peripheral blood and disease tissues of patients of SLE, RA and SjS (P < 0.05), suggesting the expanded AMB cells in those patients.

CONCLUSION

This study defines the transcriptomic signature, immune phenotypes and potential signaling pathways of AMB, and also confirms the involvement of AMB in systemic rheumatic diseases including SLE, RA and SjS via transcriptomic approaches. mTORC1 signaling and P38/MAPK signaling are promising therapeutic targets for systemic rheumatic diseases mediated by AMB.

SIV-specific antibodies protect against inflammasome-driven encephalitis in untreated macaques

Viral encephalitis is a growing public health threat with limited diagnostic and treatment options. Simian immunodeficiency virus (SIV)-infected macaques are an established model for human immunodeficiency virus (HIV), and approximately 60% of untreated pigtail macaques rapidly progress to characteristic SIV encephalitis (SIVE). The immune responses of SIV-infected macaques are investigated in plasma, cerebrospinal fluid (CSF), and brain tissue to determine correlates with SIVE pathology. Macaques with SIVE show myeloid-dominant brain lesions with inflammasome activation in infected and bystander cells, as assessed by interleukin (IL)-1β, IL-18, and apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC), and elevations in monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1α, and tumor necrosis factor alpha (TNF-α). SIV-specific immunoglobulin (Ig)G in plasma and CSF is predictive of SIVE as early as 21 days post-inoculation; animals with SIVE continue to show negligible seroconversion 3 months after infection. This dichotomy in immune responses, wherein some macaques fail to initiate robust IgG responses and subsequently develop SIVE, provides insight into the pathogenesis and heterogeneous outcomes in viral encephalitis.

The B7:CD28 family and friends: Unraveling coinhibitory interactions

Immune responses must be tightly regulated to ensure both optimal protective immunity and tolerance. Costimulatory pathways within the B7:CD28 family provide essential signals for optimal T cell activation and clonal expansion. They provide crucial inhibitory signals that maintain immune homeostasis, control resolution of inflammation, regulate host defense, and promote tolerance to prevent autoimmunity. Tumors and chronic pathogens can exploit these pathways to evade eradication by the immune system. Advances in understanding B7:CD28 pathways have ushered in a new era of immunotherapy with effective drugs to treat cancer, autoimmune diseases, infectious diseases, and transplant rejection. Here, we discuss current understanding of the mechanisms underlying the coinhibitory functions of CTLA-4, PD-1, PD-L1:B7-1 and PD-L2:RGMb interactions and less studied B7 family members, including HHLA2, VISTA, BTNL2, and BTN3A1, as well as their overlapping and unique roles in regulating immune responses, and the therapeutic potential of these insights.

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

Breg-Mediated Immunoregulation in the Skin

Wound healing is a complex process involving a coordinated series of events aimed at restoring tissue integrity and function. Regulatory B cells (Bregs) are a subset of B lymphocytes that play an essential role in fine-tuning immune responses and maintaining immune homeostasis. Recent studies have suggested that Bregs are important players in cutaneous immunity. This review summarizes the current understanding of the role of Bregs in skin immunity in health and pathology, such as diabetes, psoriasis, systemic sclerosis, cutaneous lupus erythematosus, cutaneous hypersensitivity, pemphigus, and dermatomyositis. We discuss the mechanisms by which Bregs maintain tissue homeostasis in the wound microenvironment through the promotion of angiogenesis, suppression of effector cells, and induction of regulatory immune cells. We also mention the potential clinical applications of Bregs in promoting wound healing, such as the use of adoptive Breg transfer.