 In fact, IL-5 was originally discovered as an eosinophil colony-stimulating factor, is a major regulator of eosinophil accumulation in tissues, and can modulate eosinophil behavior at every stage from maturation to survival.Mepolizumab is a monoclonal antibody against IL-5 which can reduce excessive eosinophilia.In Hodgkin lymphoma, for instance, the typically-observed eosinophilia is thought to be attributable to an increased production of IL-5.