Introduction: Interleukin-16 (IL-16) discovered in 19821, known formerly as lymphocyte chemoattractant factor (LCF) is a lymphocyte chemoattractant factor of T cell origin with selective activity for CD4+ T cells. LCF was designated interleukin-16 (IL-16) in 1995. IL-16 is a product of CD8+ cells, CD4+ cells2, eosinophils3, mast cells and epithelial cells derived from asthmatics4. Expression of IL-16 in asthmatic epithelium correlates with the number of infiltrating CD4+ T cells5. LCF was originally identified and purified from the supernatants of ConA-stimulated peripheral blood mononuclear cells (PBMC). In addition to its chemotactic activity, it is a competence growth factor selective for CD4+ T cells dependent on an interaction with CD4 for induction of functional activity. Its cDNA codes for a novel 14-kD protein into a homotetrameric form is required for induction of biologic activity. IL-16 appears in culture supernatants as a relative molecular mass (Mr) ~56,000 biologically ac