 The disorder is clonal with regard to the
production of abnormal T-cell lymphocytes not eosinophils which appear phenotypically normal.The phenotypically aberrant lymphocytes function abnormally by stimulating the proliferation and maturation of bone marrow eosinophil-precursor cells which in studied cases appears due to their excess production of interleukin 5, interleukin 3, or interleukin 13.The disorder is usually indolent but infrequently progresses to T-cell lymphoma or Sezary syndrome.