Finally, although some authors have reported elevated IL-3 in the plasma of patients with eosinophilia in conjunction with intracellular staining in CD8+ T cells (56), IL-3 is not universally detected in serum (57) of patients with HES, and the role of IL-3 as a biomarker in HES remains to be explored. This evidence concerns the gene CD8A and hypereosinophilic syndrome.