The study by Lopez et al. investigates the role of recombinant human interleukin 5 (rhIL-5) in the activation and function of human eosinophils. Eosinophilia, a condition characterized by an increase in eosinophil numbers, is observed in various allergic and parasitic conditions. The authors found that rhIL-5 selectively stimulates the morphological changes and functional activation of human eosinophils, including increased cytotoxicity, phagocytosis, and superoxide anion production. These effects were not observed in neutrophils, suggesting that rhIL-5 is a specific activator of eosinophil function. The selective activation of eosinophils by rhIL-5 may explain the observed increase in eosinophil numbers and activation in diseases such as allergy, parasitic infections, and hypereosinophilic syndromes. The production of IL-5 in vivo could have significant clinical implications, including the potential for therapeutic intervention in certain conditions.The study by Lopez et al. investigates the role of recombinant human interleukin 5 (rhIL-5) in the activation and function of human eosinophils. Eosinophilia, a condition characterized by an increase in eosinophil numbers, is observed in various allergic and parasitic conditions. The authors found that rhIL-5 selectively stimulates the morphological changes and functional activation of human eosinophils, including increased cytotoxicity, phagocytosis, and superoxide anion production. These effects were not observed in neutrophils, suggesting that rhIL-5 is a specific activator of eosinophil function. The selective activation of eosinophils by rhIL-5 may explain the observed increase in eosinophil numbers and activation in diseases such as allergy, parasitic infections, and hypereosinophilic syndromes. The production of IL-5 in vivo could have significant clinical implications, including the potential for therapeutic intervention in certain conditions.