Interleukin 16 (IL16) is a pleiotrophic cytokine derived from CD8+ T-cells that stimulates chemotaxis in CD4+ lymphocytes, monocytes, and eosinophils. It primes CD4+ T-cells for IL2 and IL15 responsiveness, induces T-lymphocyte Interleukin 2 (IL2) receptor expression, and inhibits HIV replication. The signalling process of IL16 is mediated by CD4, and undergoes proteolysis to yield two functional proteins. IL16 isoform 1 has the possible function of acting as a scaffolding protein to anchor ion channels in the membrane, while isoform 3 is involved in cell cycle progression in T-cells and transcriptional regulation of SKP2. IL16 mRNA expression levels have been found in various tissues such as spleen, bone marrow, thymus, and lymph nodes.