JCI Insight | Conserved interactions in fetal intestines underpin B cell lymphopoiesis

This study reveals the molecular and cellular mechanisms governing B cell development in fetal intestines, demonstrating that the process relies on cytokines such as TSLP and IL-7 provided by lymphoid tissue-inducer (LTi) cells and lymphatic endothelial cells (LECs). These findings challenge traditional B cell development models and offer novel insights into the early formation of mucosal immune systems.

 

Literature Overview
The article "Conserved interactions with stromal and immune cells coordinate de novo B cell lymphopoiesis in fetal intestines", published in JCI Insight, reviews and summarizes the molecular and cellular mechanisms of B cell development trajectories in fetal small intestines as a microenvironment. Using single-cell RNA sequencing, spatial transcriptomics, immunofluorescence, and high-dimensional flow cytometry, the study systematically analyzed B cell development pathways and their interactions with stromal and immune cells in human and murine fetal intestines. It further identifies evolutionarily conserved mechanisms of B cell development in fetal intestines and highlights the unique role of LTi cells in this process, distinct from fetal liver development. The article provides critical insights into the embryonic origins of intestinal immune systems.

Background Knowledge
Recent studies have gradually uncovered the complexity of the fetal immune system, yet the prenatal development of B cells and its microenvironmental regulation in the gut remain incompletely understood. Conventional paradigms posit that B cells primarily develop in bone marrow and fetal liver, but emerging evidence indicates the small intestine also supports de novo B cell generation. This study systematically characterizes cellular components and signaling pathways (e.g., CXCR4-CXCL12, IL-7R-IL-7, TSLP) sustaining B cell development in fetal intestines through human and murine models. While these factors are well-documented in bone marrow B cell development, their sources and roles in fetal intestines remain unclear. Although LTi cells' role in secondary lymphoid organogenesis is established, their contribution to B cell development was previously unknown. This research fills critical knowledge gaps regarding fetal intestinal B cell development and establishes a theoretical foundation for studying early mucosal immune system development and its interactions with microbiota.

 

 

Research Methods and Experiments
The research team systematically analyzed human and murine fetal intestinal tissues using single-cell RNA sequencing (scRNA-Seq), spatial transcriptomics, immunohistochemistry, and high-dimensional flow cytometry. By establishing rigorous immunophenotyping criteria, they mapped the complete developmental trajectory from common lymphoid progenitor (CLP) cells to mature B cells. RNAscope and immunofluorescence validated expression patterns and tissue localization of key genes (e.g., RAG2, CD19, CXCR4, IL7R). To investigate LTi cell functions in B cell development, RORγt-deficient mouse models were employed to analyze B cell developmental defects and spatial distribution changes.

Key Conclusions and Perspectives

• Complete B cell developmental trajectories exist in fetal intestines, including CLPs, pro-B, pre-B, and mature B cells, mirroring bone marrow development pathways.
• Intestinal stromal cells and lymphatic endothelial cells (LECs) highly express CXCL12, IL-7, and TSLP—factors critical for bone marrow B cell development.
• LTi cells co-localize with developing B cells in fetal intestines and promote maturation via LTα-LTBR signaling, a mechanism absent in fetal liver development.
• RORγt-deficient mice exhibit significantly reduced intestinal B cell development and diminished B-1a cell proportions, demonstrating LTi cells' tissue-specific roles in intestinal B cell ontogeny.
• Developing B cells in fetal intestines predominantly reside in the submucosa, spatially adjacent to LYVE1+ LECs and RORC+ LTi cells, suggesting specialized microenvironmental support.
• B cell developmental pathways and regulatory mechanisms in human and murine fetal intestines show high evolutionary conservation, providing experimental evidence for human intestinal immune development.

Research Significance and Prospects
This study identifies the fetal small intestine as a novel site for B cell development and elucidates its similarities and differences with bone marrow pathways. The critical roles of LTi cells and lymphatic endothelial cells establish mechanistic frameworks for understanding mucosal immune system ontogeny. Future investigations may explore how these developing B cells contribute to postnatal immune homeostasis and disease susceptibility, whether this program dysregulates in preterm infants or immunodeficient individuals, and its impact on establishing intestinal immune responses. The findings also suggest potential molecular targets for mucosal immune modulation therapies.

 

 

Conclusion
In summary, this study elucidates the molecular and cellular regulatory mechanisms underlying fetal intestinal B cell development through multi-omics and tissue localization analyses. It challenges traditional B cell development models by establishing LTi cells' indispensable role in this process. These discoveries provide a conceptual framework for understanding early intestinal immune system formation and its potential implications in developmental disorders or immunodeficiency diseases, while offering theoretical foundations for future interventions targeting intestinal immune microenvironments.

 

Kimberly A Carroll, Weihong Gu, Long Phan, Liza Konnikova, and Shruti Sharma. Conserved interactions with stromal and immune cells coordinate de novo B cell lymphopoiesis in fetal intestines. JCI Insight.