IL5 and hypereosinophilic syndrome: <h4>Background</h4>Lymphocytic-variant hypereosinophilic syndrome (L-HES) is a form of reactive hypereosinophilia, most commonly associated with interleukin-5 over-production by clonal, most commonly CD3<sup>-</sup>CD4<sup>+</sup>CD2<sup>hi</sup>CD5<sup>hi</sup>CD45RO<sup>+</sup> T-cells.