IL5 and hypereosinophilic syndrome: Lymphocytic variant hypereosinophilic syndrome (L-HES) is a distinct subtype of hypereosinophilic syndrome (HES), characterized by the presence of an aberrant or clonal T-cell population that drives eosinophil proliferation through the overproduction of eosinophil-promoting cytokines, particularly interleukin-5 (IL-5).