Expression and function of IL-7 receptors in marrow stromal cells

IL-7 was first isolated in 1988, when its role in early B lymphocyte development was noted [1-3]. It soon became apparent that IL-7 is a "stromal cytokine" produced by a variety of stromal tissues including those in bone marrow and thymus [4-10]. The production of IL-7 by bone marrow stromal cells is thought to be essential for early B lymphocyte development at least in the murine model, and secreted IL-7 from extra thymic sources including bone marrow is postulated to play a critical role in post-thymic T cell homeostasis [11-15]. Although IL-7 was thought to have effects mostly within the lymphoid populations, the demonstration of IL-7 receptors in non-lymphoid cells including primary marrow stromal cells has challenged this paradigm [15]. In this report, we present data showing that functional IL-7 receptors are expressed by marrow stroma and that IL-7 mediated signaling through this receptor is distinct from that mediated by IL-7 receptors expressed on lymphoid cells.