Expression and function of interleukin-7 in secondary and tertiary lymphoid organs

Interleukin-7 (IL-7) is known since many years as stromal-cell derived cytokine that plays a key role for the adaptive immune system. It promotes lymphocyte development in the bone marrow and thymus as well as naive and memory T cell homeostasis in the periphery. More recently, IL-7 reporter mice and other approaches have led to the further characterization of the various stromal cell sources of IL-7 in secondary lymphoid organs (SLO) and other tissues. We will review these advances along with a discussion of the regulation of IL-7 and its receptor, and compare the biological effects IL-7 has on adaptive as well as innate immune cells in SLO. Finally, we will review the role of IL-7 in development of SLO and tertiary lymphoid tissues that frequently are associated with sites of chronic inflammation.

► IL-7 receptor on lymphoid tissue inducer cells is critical for lymphoid organ development. ► Five reporter mouse strains highlight IL-7 expression within various tissues. ► IL-7 expression is frequently associated with tertiary lymphoid tissues. ► IL-7 by fibroblastic reticular cells regulates peripheral T cell homeostasis. ► IL-7R and lymph node homing molecules are co-regulated on naive T cells.