IL-5 protein, also known as Interleukin-5, is a protein molecule produced by the immune system and belongs to the category of cytokines. It is primarily expressed by T lymphocytes and other immune cells, such as NK cells. IL-5 plays a crucial role in regulating and mobilizing the body's immune response. IL-5 protein is critical for the generation, proliferation, and activation of eosinophils and basophils. These cells play significant roles in allergic diseases （such as allergic asthma and rhinitis） and certain parasitic infections. Given these characteristics of IL-5 protein, it has potential applications in in vitro diagnostics. By measuring the levels of IL-5 protein in bodily fluids, it can assist in diagnosing diseases associated with eosinophils or basophils, such as eosinophilic asthma and allergic rhinitis. These diseases are often linked to excessive expression or dysfunctional IL-5 protein. Furthermore, the level of IL-5 protein can reflect the state of the immune system.