Purity >95% as determined by SDS-PAGE. Interleukin 16 (IL-16) is produced by CD4+ and CD8+ T cells and functions as a chemoattractant for lymphocytes, monocytes, eosinophils, dendritic cells, and Langerhans cells. Additionally, IL-16 upregulates the expression of the interleukin 2 receptor (CD25), modulates T lymphocyte growth, and suppresses the replication of the human immunodeficiency virus (HIV) and simian immunodeficiency viruses (SIV).