Lymphoid stroma in the initiation and control of immune responses.

The lymphoid tissues are characterized by a complex organized architecture that is supported by a network of stromal cells. These stromal cells play many important roles in addition to serving as structural support. Lymphoid stromal cells, including the specialized fibroblastic reticular cells and follicular dendritic cells, express chemokines, cytokines, adhesion molecules, as well as other factors required for the migration, homeostasis, and survival of immune cells. Studies have demonstrated the dynamic role that lymphoid stromal cells and the chemokines they produce play in directing lymphocyte migration within the spleen and lymph nodes. The stromal network may also play roles in influencing antigen presentation, via adherence of antigen-presenting cells to the network, and cell survival, via provision of survival factors such as interleukin-7. Recently, we have shown that dramatic changes in lymphoid chemokine expression occur during many immune responses. This can alter the trafficking and localization of immune cells in lymphoid organs and has many implications for the regulation and shut-down of immune responses. Here we briefly summarize the roles of stromal cells and lymphoid architecture in the control of immune responses.