Eosinophilia associated with clonal T-cell proliferation

Eosinophilia associated with the expansion of cloned T-cells is reviewed in relation to cytokine production. It has been proved that eosinophilopoiesis is caused by eosinophil-stimulating cytokines, including interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor and interleukin-3, which are secreted from T-cells. Recently, we and other groups have reported several cases of eosinophilia including hypereosinophilic syndrome (HES) accompanied with proliferation of abnormal T-cells with an unusual phenotype CD3- CD4+ or CD3+ CD4- CD8- in the peripheral blood. The T-cells clonally proliferate, as confirmed by clonal rearrangements of the T-cell receptor (TCR) gene, and produce eosinophil-stimulating cytokines, especially IL-5, with or without stimulation in vitro. Although HES is defined by the combination of unexplained prolonged eosinophilia and evidence of organ involvement, these observations suggest that increased production of eosinophil-stimulating cytokines from the abnormal T-cells with phenotype CD3- CD4+ or CD3+ CD4- CD8- may cause eosinophilia, some of which have been diagnosed as HES.