Interleukin (IL)-4, secreted primarily by CD4(+) T cells is an immunomodulatory cytokine, which can inhibit the growth of tumour cells. IL-4 has been known as a Th2 cytokine and can act on B cells, T cells, and monocytes. Interleukin (IL)-4 exhibits antitumor activity in rodent experimental gliomas, which is likely mediated by the actions of IL-4 on a variety of immune cells present in and around the tumor masses. It participates in several B-cell activation processes as well as of other cell types. It is a costimulator of DNA-synthesis. It induces the expression of class II MHC molecules on resting B-cells. It enhances both secretion and cell surface expression of IgE and IgG1. It also regulates the expression of the low affinity Fc receptor for IgE (CD23) on both lymphocytes and monocytes. Recombinant Human IL-4 produced in E. coli is a single, non-glycosylated polypeptide chain containing 130 amino acids and having a molecular mass of 15,000 Daltons.