[Th2 lymphocytes in man: a new cause of hypereosinophilic syndrome].

Interleukin-5 produced by Th2-type lymphocytes is involved in the pathogenesis of several hypereosinophilic disorders. We have identified clonal Th2 cells in the peripheral blood of three patients with the idiopathic hypereosinophilic syndrome. Costimulatory signaling through B7/CD28 and LFA-3/CD2 pathways cooperates with an autocrine interleukin-2/interleukin-2 receptor loop for the survival and proliferation of these Th2 cells, as well as their production of cytokines, independently of T cell receptor engagement. The high-level of spontaneous apoptosis displayed by these cells was inhibited by interleukin-2 and interferon-g. New therapeutic strategies could result from our observations. Indeed, the hypereosinophilic syndrome may represent an unexpected indication for new immunomodulatory molecules such as CTLA4-Ig and anti-il-2 receptor antibodies.