Interleukin 16 and its function as a CD4 ligand

The secreted form of interleukin 16 (IL-16) is a 14 kDa protein that multimerizes into homotetramers essential for CD4-dependent signaling and cellular functions. As reviewed here by David Center and colleagues, IL-16 is a chemoattractant factor for all CD4(+) leukocytes and is a competence growth factor for CD4(+) T cells, implying that it might play a role in accumulation and activation of CD4(+) immune cells at sites if inflammation.