Hematopoietic cytokine that plays an essential role in the development, expansion, and survival of naive and memory T-cells and B-cells thereby regulating the number of mature lymphocytes and maintaining lymphoid homeostasis. Mechanistically, exerts its biological effects through a receptor composed of IL7RA subunit and the cytokine receptor common subunit gamma/CSF2RG. Binding to the receptor leads to activation of various kinases including JAK1 or JAK3 depending on the cell type and subsequently propagation of signals through activation of several downstream signaling pathways including the PI3K/Akt/mTOR or the JAK-STAT5. Interacts with IL7R and CSF2RG. Three disulfide bonds are present. Belongs to the IL-7/IL-9 family.