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. May act as a scaffolding protein that anchors ion channels in the membrane. Isoform 3 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). According to PubMed:9699630, the formation of a homotetrameric protein complex is not required for the chemo-attractant function. Isoform 3 interacts (via PDZ 3 domain) with PPP1R12A, PPP1R12B and PPP1R12C. Isoform 1 interacts with PPP1R12B. Isoform 3 interacts with GRIN2A. Isoform 3 interacts with GABPB1. Isoform 3 interacts (via PDZ 3 domain) with HDAC3. Isoform 1 interacts with GRIN2D, KCNJ10, KCNJ15 and CACNA1C (By similarity). (Microbial infection) Isoform 3 interacts with HTLV-1 tax. Expressed in hemopoietic tissues, such as resting T-cells, but undetectable during active T-cell proliferation. Down-regulated in T-cells after TCR activation. Synthesized as a chemo-attractant inactive precursor in hemopoietic tissues, and 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 splicing of isoform 1. Is probably proteolytically processed to yield IL-16. Produced by alternative promoter usage. Is proteolytically processed to yield IL-16.