The biological effects of IL7 are mediated by the binding of IL7 to the specific cell surface receptor. The functional high-affinity IL7 receptor consists of an alpha chain and a gamma chain. Both IL7R alpha and IL7R gamma are members of the hematopoietin receptor superfamily. IL7R alpha cDNA encodes a precursor protein containing a signal peptide, an extracellular ligand binding domain, a transmembrane region, and a cytoplasmic region. IL7R alpha transcripts have been observed in spleen, thymus, fetal liver, developing T cells, B cells, mature T cells, and bone marrow derived macrophages.