IL5RA and parasitic infectious disease: The ability to maintain normal functionality in the absence of eosinophils is not well understood but may involve redundancy in host defence mechanisms (e.g., mast cells fulfilling the role of defence against parasitic infections), sparing of certain eosinophil types such as regulatory or homeostatic eosinophils by IL-5/IL-5R-targeted treatments, and/or possible persistence of IL-5R-expressing eosinophils in tissue.