Cytokine networks driving eosinophil functional heterogeneity

Eosinophils have traditionally been viewed as terminally differentiated type 2 effector cells involved in anti-helminth immunity and allergic inflammation. Recent advances in single-cell transcriptomics have refined this view, revealing substantial developmental and functional heterogeneity across tissues and inflammatory settings. Eosinophil development in the bone marrow is controlled by lineage-defining transcription factors and by cytokines such as IL-5, IL-3, GM-CSF and IL-33, which regulate progenitor expansion, maturation, mobilization and survival. After entering tissues, eosinophils integrate local cytokine, stromal, epithelial, microbial and metabolic signals to acquire context-dependent activation states. In this review, we summarize core developmental programs of eosinophils and examine how cytokine networks shape their responses across type 1, type 2 and type 17 immunity. We discuss evidence that eosinophils contribute not only to classical type 2 responses, but also to antimicrobial, cytotoxic, immunoregulatory and tissue-remodeling programs in non-type 2 settings, positioning them as highly plastic effectors with broad roles in host defense, tissue homeostasis and disease.