CD39 and CD326 Are Bona Fide Markers of Murine and Human Plasma Cells and Identify a Bone Marrow Specific Plasma Cell Subpopulation in Lupus

Recruitment of plasma cells from IL-21-dependent and IL-21-independent immune reactions to the bone marrow

Bone marrow plasma cells (BMPC) are the correlate of humoral immunity, consistently releasing antibodies into the bloodstream. It remains unclear if BMPC reflect different activation environments or maturation of their precursors. Here we define human BMPC heterogeneity and track the recruitment of antibody-secreting cells (ASC) from SARS-CoV-2 vaccine immune reactions to the bone marrow (BM). Trajectories based on single-cell transcriptomes and repertoires of peripheral and BM ASC reveal sequential colonisation of BMPC compartments. In activated B cells, IL-21 suppresses CD19 expression, indicating that CD19low-BMPC are derived from follicular, while CD19high-BMPC originate from extrafollicular immune reactions. In primary immune reactions, both CD19low- and CD19high-BMPC compartments are populated. In secondary immune reactions, most BMPC are recruited to CD19high-BMPC compartments, reflecting their origin from extrafollicular reactivations of memory B cells. A pattern also observable in vaccinated-convalescent individuals and upon diphtheria/tetanus/pertussis recall-vaccination. Thus, BMPC diversity reflects the evolution of a given humoral immune response.

Temporal Tracking of Plasma Cells in vivo Using J-chain CreERT2 Reporter System

Plasma cells (PCs) are essential for humoral immunity, as they are responsible for the production of antibodies and contribute to immunological memory. Despite their importance, differentiating between long-lived and short-lived PCs in vivo remains a challenge due to a lack of specific markers to distinguish these populations. Addressing this gap, our study introduces a novel J-chain CreERT2 GFP allele (IgJCreERT2) for precise genetic studies of PCs. This model takes advantage of PC-restricted expression of the J-chain gene, enabling temporal and cell-specific tracking of PCs utilizing a tamoxifen-inducible Cre recombinase. Our in vitro and in vivo validation studies of the inducible Cre allele confirmed the fidelity and utility of this model and demonstrated the model's ability to trace the long-lived PC population in vivo following immunization. The IgJCreERT2 model allowed for detailed analysis of surface marker expression on PCs, revealing insights into PC heterogeneity and characteristics. Our findings not only validate the IgJCreERT2 mouse as a reliable tool for studying PCs but also facilitate the investigation of PC dynamics and longevity, particularly in the context of humoral immunity and vaccine responses. This model represents a significant advancement for the in-depth study of PCs in health and disease, offering a new avenue for the exploration of PC biology and immunological memory.

From bench to bedside: targeting lymphocyte activation gene 3 as a therapeutic strategy for autoimmune diseases

BACKGROUND

Immune checkpoints negatively regulate immune response, thereby playing an important role in maintaining immune homeostasis. Substantial studies have confirmed that blockade or deficiency of immune checkpoint pathways contributes to the deterioration of autoimmune diseases. In this context, focusing on immune checkpoints might provide alternative strategies for the treatment of autoimmunity. Lymphocyte activation gene 3 (LAG3), as a member of immune checkpoint, is critical in regulating immune responses as manifested in multiple preclinical studies and clinical trials. Recent success of dual-blockade of LAG3 and programmed death-1 in melanoma also supports the notion that LAG3 is a crucial regulator in immune tolerance.

METHODS

We wrote this review article by searching the PubMed, Web of Science and Google Scholar databases.

CONCLUSION

In this review, we summarize the molecular structure and the action mechanisms of LAG3. Additionally, we highlight its roles in diverse autoimmune diseases and discuss how the manipulation of the LAG3 pathway can serve as a promising therapeutic strategy as well as its specific mechanism with the aim of filling the gaps from bench to bedside.

Efficient CRISPR-Cas9-mediated mutagenesis in primary human B cells for identifying plasma cell regulators

Human B lymphocytes are attractive targets for immunotherapies in autoantibody-mediated diseases. Gene editing technologies could provide a powerful tool to determine gene regulatory networks regulating B cell differentiation into plasma cells, and identify novel therapeutic targets for prevention and treatment of autoimmune disorders. Here, we describe a new approach that uses CRISPR-Cas9 technology to target genes in primary human B cells in vitro for identifying plasma cell regulators. We found that sgRNA and Cas9 components can be efficiently delivered into primary human B cells through RD114-pseudotyped retroviral vectors. Using this system, we achieved approximately 80% of gene knockout efficiency. We disrupted expression of a triad of transcription factors, IRF4, PRDM1, and XBP1, and showed that human B cell survival and plasma cell differentiation are severely impaired. Specifically, that IRF4, PRDM1, and XBP1 were expressed at different stages during plasma cell differentiation, IRF4, PRDM1, and XBP1-targeted B cells failed to progress to the pre-plasmablast, plasma cell state, and plasma cell survival, respectively. Our method opens a new avenue to study gene functions in primary human B cells and identify novel plasma cell regulators for therapeutic applications.

Low-Level Expression of CD138 Marks Naturally Arising Anergic B Cells

Autoreactive B cells are not entirely deleted, but some remain as immunocompetent or anergic B cells. Although the persistence of autoreactive B cells as anergic cells has been shown in transgenic mouse models with the expression of B cell receptor (BCR) reactive to engineered self-antigen, the characterization of naturally occurring anergic B cells is important to identify them and understand their contribution to immune regulation or autoimmune diseases. We report here that a low-level expression of CD138 in the splenic B cells marks naturally arising anergic B cells, not plasma cells. The CD138^int B cells consisted of IgM^lowIgD^high follicular (FO) B cells and transitional 3 B cells in homeostatic conditions. The CD138^int FO B cells showed an anergic gene expression profile shared with that of monoclonal anergic B cells expressing engineered BCRs and the gene expression profile was different from those of plasma cells, age-associated B cells, or germinal center B cells. The anergic state of the CD138^int FO B cells was confirmed by attenuated Ca²⁺ response and failure to upregulate CD69 upon BCR engagement with anti-IgM, anti-IgD, anti-Igκ, or anti-IgG. The BCR repertoire of the CD138^int FO B cells was distinct from that of the CD138^- FO B cells and included some class-switched B cells with low-level somatic mutations. These findings demonstrate the presence of polyclonal anergic B cells in the normal mice that are characterized by low-level expression of CD138, IgM downregulation, reduced Ca²⁺ and CD69 responses upon BCR engagement, and distinct BCR repertoire.

Hydroxychloroquine induces apoptosis of myeloid-derived suppressor cells via up-regulation of CD81 contributing to alleviate lupus symptoms

Background

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that results from widespread immune complex deposition and secondary tissue injury. Hydroxychloroquine (HCQ) has been used clinically to treat SLE, while its exact mechanism has still remained elusive. Some studies have shown that myeloid-derived suppressor cells (MDSCs) play a vital role in the regulation of SLE. In this study, we aimed to explore the effects of HCQ on the apoptosis of MDSCs in lupus mice and its possible molecular regulatory mechanism.

Methods

We constructed the imiquimod (IMQ)-induced lupus model in mice. The proportion and apoptosis of MDSCs were measured by flow cytometry. CD81-overexpressed adeno-associated virus was intraperitoneally injected into the lupus mice. We also transfected the CD81 siRNA into bone marrow-derived MDSCs, and employed qRT-PCR and Western blotting to quantify the level of CD81.

Results

The results showed that HCQ ameliorated IMQ-induced lupus symptoms, and simultaneously inhibited the expansion of MDSCs. In particular, HCQ induced the apoptosis of MDSCs, and also up-regulated the expression level of CD81 in MDSCs, which might indicate the relationship between the expression level of CD81 and the apoptosis of MDSCs. CD81 was further confirmed to participate in the apoptosis of MDSCs and lupus disease progression by overexpressing CD81 in vivo. Molecular docking experiment further proved the targeting effect of HCQ on CD81. And then we interfered CD81 in bone marrow derived MDSCs in vitro, and it was revealed that HCQ rescued the decreased expression level of CD81 and relieved the immune imbalance of Th17/Treg cells.

Conclusion

In summary, HCQ promoted the apoptosis of MDSCs by up-regulating the expression level of CD81 in MDSCs, and ultimately alleviated lupus symptoms. Our results may assist scholars to develop further effective therapies for SLE.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00493-6.