Homodimeric cytokine expressed predominantly by T-lymphocytes and NK cells that plays an important role in the survival, differentiation, and chemotaxis of eosinophils (PubMed:2653458, PubMed:9010276). Also acts on activated and resting B-cells to induce immunoglobulin production, growth, and differentiation (By similarity). Mechanistically, exerts its biological effects through a receptor composed of IL5RA subunit and the cytokine receptor common subunit beta/CSF2RB (PubMed:1495999, PubMed:22528658). Binding to the receptor leads to activation of various kinases including LYN, SYK and JAK2 and thereby propagates signals through the RAS-MAPK and JAK-STAT5 pathways respectively (PubMed:7613138). {ECO:0000250|UniProtKB:P04401, ECO:0000269|PubMed:1495999, ECO:0000269|PubMed:22528658, ECO:0000269|PubMed:2653458, ECO:0000269|PubMed:7613138, ECO:0000269|PubMed:9010276}. This is the function of IL5 (interleukin 5, ENSG00000113525).