A case of hypereosinophilic syndrome is associated with the expansion of a CD3(-)CD4(+) T-cell population able to secrete large amounts of interleukin-5

Interleukin-5 (IL-5) is the major soluble factor able to mediate hypereosinophilia. We report a case of hypereosinophilic syndrome in which the presence of a population of CD3(-)CD4(+) cells able to overproduce IL-5 was shown. The lack of CD3 and TCRAB membrane expression on otherwise phenotypically normal mature T lymphocytes together with the absence of detectable TCRBV mRNA and clonal rearrangement of TCRB gene suggested that the abnormal lymphocyte population was the expression of a peripheral T-cell lymphoma with an indolent clinical course, Peripheral blood lymphocytes enriched in this population were able to secrete high levels of IL-5 but not of IL-4, and no IL-2 or interferon-gamma, when stimulated in vitro with phytohemagglutinin and phorbol myristate acetate, The serum contained eosinophil survival factors whose activity was partially neutralized by a specific antihuman IL-5 antibody, This observation further emphasized the relationship between hypereosinophilic syndrome, IL-5, and T-cell lymphoproliferative disorders. (C) 1996 by The American Society of Hematology.