Why lymph nodes grow

At the initiation of an immune response, lymph nodes can double in size in a day and can be ten times their original size in five to seven days. Webster and colleagues report on page 1903 that dendritic cells, quite distinct from their function in antigen presentation, stimulate endothelial cell proliferation and vascular growth in the growing lymph node.

Peripheral challenge (such as immunization) induces dendritic cells to mature and migrate to the lymph nodes. But what is their role once there? Dendritic cells are well known for their role in B and T cell lymphocyte stimulation but, surprisingly, Lu's team found that without lymphocytes (in Rag^−/− mice) dendritic cells could activate lymph node growth and endothelial cell proliferation almost as effectively.

Vascular endothelial growth factor (VEGF) has been implicated in...