Interleukin 16 (IL-16) is a pleiotropic cytokine that has been characterized as a chemoattractant for certain immune cells expressing the cell surface molecule CD4, and it has effects on mixed lymphocyte reaction and inhibition of HIV viral replication. Because this cytokine was discovered in 1982 for its T lymphocyte chemotactic activity, it was named “Lymphocyte Chemoattractant Factor (LCF)” until it was designated interleukin-16.
IL-16 forms homotetramers and this structure is required for its bioactivity. The cytokine function is exclusively attributed to the secreted C-terminal peptide, while the N-terminal product may play a role in cell cycle control.
IL-16 is released by a variety of immune (T cells, esinophils, and dendritic cells) and non-immune (fibroblasts, epithelial, and neurona) cells. In the non-diseased state, IL-16 mRNA is almost exclusively expressed on lymphatic tissue, and high levels in T cells. During inflammation, IL-16 is synthesized in a number of other tissues. The sequence, structure, and function of IL-16 are highly conserved in all species examined. Thus far, all species of IL-16 tested induce similar bioactivities on CD4+ T cells.