Eosinophilic interleukin 5 (IL‐5) transgenic mice: eosinophil activity and impaired clearance of Schistosoma mansoni

Eosinophilia is a feature common to many invasive helminth infections and eosinophils are often considered to be effector cells in immunity to helminths. This study examined the possible influence of constituitive eosinophilia on the clearance of Schistosoma mansoni infections in mice. Eosinophils from interleukin‐5 transgenic mice exhibit normal ultrastructure and function with regard to phagocytosis and killing of bacteria and responses to chemotactic stimuli. IL‐5 transgenics and non‐transgenic littermates were immunized once or four (hyperimmunization) times with irradiated cercariae of S. mansoni. Animals were challenged percutaneously with unirradiated cercariae one month after their last exposure to irradiated parasites. One month after challenge transgenic animals, whether unimmunized, vaccinated or hypervaccinated, carried significantly more liver‐stage parasites than non‐transgenic animals. These results suggest that although eosinophils from IL‐5 transgenic mice are functional for a number of key parameters, large numbers of eosinophils and/or high levels of IL‐5 may in some way impair clearance of S. mansoni. A re‐evaluation of the roles of eosinophils and IL‐5 in infections with this and other parasites may therefore be warranted.