Human IL-5 has been described as T-cell replacing factor and as B-cell growth factor II based on its induction of proliferation and Ig secretion by activated B cells. Several other activities have furthermore been attributed to this cytokine, including induction of growth and differentiation of eosinophils from bone marrow stem cells, induction of mIL-2R expression on activated B cells and enhancements of IgA secretion by LPS-stimulated B-cells. IL-5 has been shown to be produced by the TH2 subset of human TH clones. The spectrum of biological activities of IL-5, on B cells as well as other cell types suggests that IL-5 plays an important functional role in the activities of TH2 cells. IL-5 is a heavily glycosylated glycoprotein with a native molecular weight of 45 to 60 kDa, with multiple subunits of 24 to 28 kDa under reducing conditions.

Synonyms: T-cell replacing factor, TRF, Eosinophil differentiation factor, Bcell differentiation factor