Interleukin 16 (IL-16) is a cytokine that is released by a variety of cells (including lymphocytes and some epithelial cells) that has been characterized as a chemoattractant for certain immune cells expressing the cell surface molecule CD4. IL-16 was originally described as a factor that could attract activated T cells in humans, it was previously called lymphocyte chemoattractant factor (LCF). Since then, IL-16 has been shown to recruit and activate many other cells expressing the CD4 molecule, including monocytes, eosinophils, and dendritic cells. The protein encoded by this gene is a pleiotropic cytokine that functions as a chemoattractant, a modulator of T cell activation, and an inhibitor of HIV replication. The signaling process of this cytokine is mediated by CD4.
IL-16 expression has been linked to inflammation processes in asthma, rheumatoid arthritis, systemic lupus erythematosus, colitis, atopic dermatitis, and multiple sclerosis. For example, the expression of IL-16 directly correlates with the number of infiltrating CD4 T cells in asthmatic epithelium.