IL-5 is a key regulator of eosinophilia.
References
Foster PS, Hogan SP, Yang M, Mattes J, Young IG, Matthaei KI, Kumar RK, Mahalingam S, Webb DC. Interleukin-5 and eosinophils as therapeutic targets for asthma. Trends Mol Med. 2002 Apr;8(4):162-7. PMID: #11927273#