Do multiple subsets of CD11c+ B cells exist? You (T)-Bet!

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.

Multiomics dissection of human RAG deficiency reveals distinctive patterns of immune dysregulation but a common inflammatory signature

Human recombination-activating gene (RAG) deficiency can manifest with distinct clinical and immunological phenotypes. By applying a multiomics approach to a large group of RAG-mutated patients, we aimed at characterizing the immunopathology associated with each phenotype. Although defective T and B cell development is common to all phenotypes, patients with hypomorphic RAG variants can generate T and B cells with signatures of immune dysregulation and produce autoantibodies to a broad range of self-antigens, including type I interferons. T helper 2 (TH2) cell skewing and a prominent inflammatory signature characterize Omenn syndrome, whereas more hypomorphic forms of RAG deficiency are associated with a type 1 immune profile both in blood and tissues. We used cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) analysis to define the cell lineage-specific contribution to the immunopathology of the distinct RAG phenotypes. These insights may help improve the diagnosis and clinical management of the various forms of the disease.

Emerging insights into atypical B cells in pediatric chronic infectious diseases and immune system disorders: T(o)-bet on control of B-cell immune activation

Repetitive or persistent cellular stimulation in vivo has been associated with the development of a heterogeneous B-cell population that exhibits a distinctive phenotype and, in addition to classical B-cell markers, often expresses the transcription factor T-bet and myeloid marker CD11c. Research suggests that this atypical population consists of B cells with distinct B-cell receptor specificities capable of binding the antigens responsible for their development. The expansion of this population occurs in the presence of chronic inflammatory conditions and autoimmune diseases where different nomenclatures have been used to describe them. However, as a result of the diverse contexts in which they have been investigated, these cells have remained largely enigmatic, with much ambiguity remaining regarding their phenotype and function in humoral immune response as well as their role in autoimmunity. Atypical B cells have garnered considerable interest because of their ability to produce specific antibodies and/or autoantibodies and because of their association with key disease manifestations. Although they have been widely described in the context of adults, little information is present for children. Therefore, the aim of this narrative review is to describe the characteristics of this population, suggest their function in pediatric immune-related diseases and chronic infections, and explore their potential therapeutic avenues.