Identification of a novel receptor/signal transduction pathway for IL-15/T in mast cells.

Interleukin-15/T(IL-15) is a growth factor that utilizes IL-2 receptor (IL-2R) components in addition to its private binding protein IL-15R(alpha) in T-cells. Here, we report that IL-15 induces mast cell proliferation in the absence of IL-2R alpha and beta. Using transfectants of these cells with a cytoplasmic-truncated mutant of gamma(c), we demonstrated that IL-15 signaling in mast cells does not involve gamma(c). Cross-linking of mast cells with (125)I]IL-15 revealed a 60-65 kDa IL-15 binding protein that is distinct from known components of T-cell IL-15 receptors. Mast cell IL-15 receptors recruit JAK-2 and STAT-5, instead of JAK1/3 and STAT3/5 that are activated in T-cells. Thus IL-15 is a mast cell growth factor that utilizes a novel receptor and distinct signaling pathway.