IL-16 has been reported to up-regulate the IL-2 receptor (CD25), induce progression of cells to the G (1) phase and suppress HIV & SIV replication. Other cells which have been shown to express IL-16 are: B-cells, eosinophils, macrophages, epithelial cells, fibroblasts, microglial cells and keratinocytes. Human and murine IL-16 share a high degree of structural and functional similarity. rHu IL-16 produced in E. coli is comprised of 130 amino acids with a molecular weight of 13.5 kDa.