IL-5 is a homodimeric, disulphide-linked protein produced by T-cells. The native protein can have variable molecular weight as a result of glycosylation. Monomeric mouse IL-5 is a 113 amino acid protein with a reported molecular weight of 35-37 kD for the homodimeric protein. Mouse and human IL-5 are approximately 70% identical. IL-5 has been shown to promote the growth of immature hematopoietic BFU-E progenitors and stimulates the activation, and differentiation of eosinophils, and promotes the generation of cytotoxic lymphocytes . Mouse IL-5 induces the differentiation and proliferation of pre-activated B-cells and stimulates the production and secretion of IgM and IgA by B-cells stimulated with bacterial endotoxin.