Abnormal clones of T cells producing interleukin-5 in idiopathic eosinophilia

Background The cause of persistent eosinophilia and the hypereosinophilic s yndrome is unknown. Recent work suggests that in some patients with the hyp ereosinophilic syndrome, a clone of abnormal T cells produces large amounts of interleukin-5, a cytokine required for the growth and differentiation o f eosinophils. We examined T-cell surface markers, rearranged T-cell-recept or genes, and in vitro production of cytokines by T cells from patients wit h idiopathic eosinophilia. Methods The expression of surface molecules on T cells was measured by flow cytometry. Cytokine expression was measured by enzyme-linked immunosorbent assay, flow cytometry, and immunohistochemical analysis. To identify domin ant (clonal) rearrangements of the T-cell receptor within the lymphocyte po pulation, Southern blot analysis (beta chain) and the polymerase chain reac tion (gamma chain) were performed according to standard protocols. Results Among 60 patients with idiopathic eosinophilia, 16 had circulating T cells with an aberrant immunophenotype. In each of these patients, the ab normal immunophenotype was unique. Evidence of clonal rearrangements of the T-cell receptor was obtained in 8 of the 16 patients. In most instances, t he abnormal T cells expressed large amounts of surface proteins associated with T-cell activation (the a chain of the interleukin-2 receptor and the H LA-DR antigen). Moreover, the aberrant T cells produced large amounts of in terleukin-5 in vitro. Conclusions Clonal populations of abnormal T cells producing interleukin-5 occur in some patients with idiopathic eosinophilia. (N Engl J Med 1999;341 :1112-20.) (C)1999, Massachusetts Medical Society.