Interleukin-16 stimulates a migratory response in CD4+ lymphocytes, monocytes, and eosinophils. Primes CD4+ T-cells for IL-2 and IL-15 responsiveness. Also induces T-lymphocyte expression of interleukin 2 receptor. Ligand for CD4. Isoform 1 may act as a scaffolding protein that anchors ion channels in the membrane. Isoform 2 is involved in cell cycle progression in T-cells. Appears to be involved in transcriptional regulation of SKP2 and is probably part of a transcriptional repression complex on the core promoter of the SKP2 gene. May act as a scaffold for GABPB1 (the DNA-binding subunit the GABP transcription factor complex) and HDAC3 thus maintaining transcriptional repression and blocking cell cycle progression in resting T-cells. Homotetramer (Probable). Isoform 2 interacts with GRIN2A. Isoform 1 interacts with GRIN2D, KCNJ10, KCNJ15 and CACNA1C. Isoform 2 interacts (via PDZ 3 domain) with PPP1R12A, PPP1R12B and PPP1R12C. Isoform 1 interacts with PPP1R12B. Isoform 3 interacts with GABPB1. Isoform 2 interacts (via PDZ 3 domain) with HDAC3 (By similarity). Colocalizes with GRIN2C in neuronal cell bodies and neurites. Isoform 1 is expressed in neurons of the cerebellum and hippocampus. Isoform 2 is expressed in thymus, spleen and lung. Synthesized as a chemo-attractant inactive precursor which is proteolytically cleaved by caspase-3 to yield IL-16. Produced by alternative promoter usage. Is probably proteolytically processed to yield IL-16. Produced by alternative promoter usage. Is proteolytically processed to yield IL-16.