Thymus antibody-secreting cells possess an interferon gene signature and are preferentially expanded in young female mice

Highlights of 2024: New insights into the molecular regulation of antibody-secreting cells and their subsets

Collectively, 2024 has significantly increased the wealth of knowledge regarding antibody-secreting cell heterogeneity in health and disease. This 'Highlights of 2024' article discusses key studies contributing to the understanding of how tissue residency and disease state influence the transcriptional programming of antibody-secreting cell phenotypes.

Antigen presentation for central tolerance induction

The extent of central T cell tolerance is determined by the diversity of self-antigens that developing thymocytes 'see' on thymic antigen-presenting cells (APCs). Here, focusing on insights from the past decade, we review the functional adaptations of medullary thymic epithelial cells, thymic dendritic cells and thymic B cells for the purpose of tolerance induction. Their distinct cellular characteristics range from unconventional phenomena, such as promiscuous gene expression or mimicry of peripheral cell types, to strategic positioning in distinct microenvironments and divergent propensities to preferentially access endogenous or exogenous antigen pools. We also discuss how 'tonic' inflammatory signals in the thymic microenvironment may extend the intrathymically visible 'self' to include autoantigens that are otherwise associated with highly immunogenic peripheral environments.

Highlight of 2023: Thymic B cells-important players in the establishment of T-cell tolerance

In this article for the Highlights of 2023 Series, we discuss four recent articles that investigated thymic B cells, in both mice and humans. These studies provide important novel insights into the biology of this unique B-cell population, from their activation and differentiation to their role in promoting the negative selection of thymocytes and the generation of regulatory T cells.

Jchain-DTR Mice Allow for Diphtheria Toxin-Mediated Depletion of Antibody-Secreting Cells and Evaluation of Their Differentiation Kinetics

Antibody-secreting cells (ASCs) are generated following B cell activation and constitutively secrete antibodies. As such, ASCs are key mediators of humoral immunity whether it be in the context of pathogen exposure, vaccination or even homeostatic clearance of cellular debris. Therefore, understanding basic tenants of ASC biology such as their differentiation kinetics following B cell stimulation is of importance. Towards that aim, we developed a mouse model which expresses simian HBEGF (a.k.a., diphtheria toxin receptor (DTR)) under the control of the endogenous Jchain locus (or J-DTR). ASCs from these mice expressed high levels of cell surface DTR and were acutely depleted following diphtheria toxin treatment. Furthermore, proof-of-principle experiments demonstrated the ability to use these mice to track ASC reconstitution following depletion in 3 distinct organs. Overall, J-DTR mice provide a new and highly effective genetic tool allowing for the study of ASC biology in a wide range of potential applications.

Tfl deletion induces extraordinary Cxcl13 secretion and cachexia in VavP-Bcl2 transgenic mice

STATEMENT OF SIGNIFICANCE

Loss of TFL, found in several types of lymphoma, induces excessive CXCL13 secretion through RNA dysregulation contributing to body weight loss and early death in lymphoma model mice. Follicular lymphoma (FL) is associated with overexpressed BCL-2 and other genetic aberrations, including 6q-. We identified a novel gene on 6q25, "Transformed follicular lymphoma (TFL)," from a transformed FL. TFL regulates several cytokines via mRNA degradation, which has been suggested to underlie resolving inflammation. Fluorescence in situ hybridization revealed a deletion of TFL occurred in 13.6% of various B-cell lymphoma samples. We developed VavP-bcl2 transgenic, TFL deficit mice (Bcl2-Tg/Tfl -/-) to seek how TFL affects disease progression in this lymphoma model. While Bcl2-Tg mice developed lymphadenopathy and died around 50 weeks, Bcl2-Tg/Tfl -/- mice lost body weight around 30 weeks and died about 20 weeks earlier than Bcl2-Tg mice. Furthermore, we found a unique B220-IgM+ cell population in the bone marrow of Bcl2-Tg mice. cDNA array in this population revealed that Cxcl13 mRNA in Bcl2-Tg/Tfl -/- mice expressed significantly higher than Bcl2-Tg mice. In addition, bone marrow extracellular fluid and serum showed an extremely high Cxcl13 concentration in Bcl2-Tg/Tfl -/- mice. Among bone marrow cells, the B220-IgM+ fraction was the main producer of Cxcl13 in culture. A reporter assay demonstrated TFL regulates CXCL-13 via induction of 3'UTR mRNA degradation in B lineage cells. These data suggest Tfl regulates Cxcl13 in B220-IgM+ cells in the bone marrow, and a very high concentration of serum Cxcl13 arising from these cells may contribute to early death in lymphoma-bearing mice. Since several reports have suggested the association of CXCL13 expression with lymphoma, these findings provide new insights into cytokine regulation via TFL in lymphoma.

Retro-orbital CD45 antibody labeling to evaluate antibody-secreting cell trafficking in mice

Antibody-secreting cells (ASCs) are critical regulators of the humoral immune response. However, differences between tissue resident populations versus those that have recently migrated to their final anatomic destination are poorly understood. Here, we present a protocol for using retro-orbital (r.o.) CD45 antibody labeling to identify tissue resident versus recently immigrated ASCs in mice. We describe steps for r.o. injection of antibodies, animal euthanasia, and tissue harvesting. We then detail tissue processing, cell counting, and cell staining for flow cytometry analysis. For complete details on the use and execution of this protocol, please refer to Pioli et al. (2023).¹.

Thymus antibody-secreting cells: once forgotten but not lost

Antibody-secreting cells are essential contributors to the humoral response. This is due to multiple factors which include: 1) the ability to secrete thousands of antibodies per second, 2) the ability to regulate the immune response and 3) the potential to be long-lived. Not surprisingly, these cells can be found in numerous sites within the body which include organs that directly interface with potential pathogens (e.g., gut) and others that provide long-term survival niches (e.g., bone marrow). Even though antibody-secreting cells were first identified in the thymus of both humans and rodents in the 1960s, if not earlier, only recently has this population begun to be extensively investigated. In this article, we provide an update regarding the current breath of knowledge pertaining to thymus antibody-secreting cells and discuss the potential roles of these cells and their impact on health.