IL5 and autoimmune disease: Common causes of eosinophilia include parasitic, allergic, autoimmune, connective tissue, and rheumatic diseases.[8] Based on the overproduction of cytokines, such as interleukin-4 and interleukin-5, cGvHD may be a Th-2-mediated process[10]; moreover, an association between increased eosinophils and cGvHD has been noted.[11] Screening for autoimmune diseases yielded negative results, and no apparent reactive cause was identified.