Interleukin-16 (IL-16) is a cytokine that plays a key role in regulating immune responses and inflammation. It is produced by various immune cells, including CD4+ T cells, mast cells, and eosinophils. IL-16 functions as a chemoattractant for CD4+ T cells, promoting their migration to sites of inflammation. Additionally, IL-16 can modulate the activation and proliferation of CD4+ T cells, as well as other immune cells, through interactions with its receptor, CD4. This cytokine is involved in the pathogenesis of various inflammatory conditions, autoimmune diseases, and cancer.
IL-16 exists in two isoforms: the full-length 130 amino acid (130aa) isoform and a shorter 121 amino acid (121aa) isoform. The 130aa isoform is the canonical form of IL-16 and is known for its chemoattractant and immunomodulatory functions. On the other hand, the 121aa isoform lacks the CD4-binding domain present in the 130aa isoform, resulting in reduced CD4-binding capacity and altered biological activity. The 121aa isoform may exhibit different chemotactic properties and signaling capabilities compared to the full-length 130aa isoform.