Specific Fibroblast Subtype Helps Organize Immune Responses in Lymph Nodes

A research group led by Sanjiv Luther at the University of Lausanne has identified a specific fibroblast subtype that helps organize immune cells within lymph nodes. Published in Immunity, the study adds to understanding of how lymph node structure supports immune responses to infection and cancer.

Lymph nodes are small organs that monitor lymph and help coordinate immune defenses. They contain distinct regions for different immune cell types, but how this spatial organization is established has remained unclear for some cells. The new study focuses on the central region of the lymph node and shows that a fibroblast subtype marked by MAdCAM1⁺ expression plays an important role in shaping that area.

The researchers examined cytotoxic T lymphocytes, which are activated during infection or cancer and can differentiate into killer cells. These cells are typically found in the central region of the lymph node, where they interact with type 1 dendritic cells. According to the study, the MAdCAM1⁺ fibroblasts produce high levels of Ccl19, a signaling molecule that attracts cytotoxic T lymphocytes and helps bring them into contact with type 1 dendritic cells.

The team also identified the signals that maintain this fibroblast population. A pathway involving Notch2 and RBPj preserves the identity and activity of the fibroblast subtype, while Jagged-1, produced mainly by type 1 dendritic cells, helps start the process. The researchers found that this molecular cascade must remain active throughout life to support proper immune cell organization. In mice lacking Notch2 expression in fibroblasts, cytotoxic T lymphocytes did not develop efficiently into memory T cells, which are needed when the same pathogen returns or the same tumor recurs.

Although the work centered on lymph nodes, the same mechanism was also observed in the spleen and Peyer’s patches. Similar cell structures and interactions were identified in human lymph nodes as well, suggesting that the Notch2 dependence of Ccl19-producing fibroblasts is conserved across species.