Synthesis of type 1 (IFN gamma) and type 2 (IL-4, IL-5, and IL-10) cytokines by human eosinophils.

Eosinophils are not only the source of cytotoxic and proinflammatory mediators but they can also generate cytokines and growth factors, including their own factors of differentiation, namely IL-3, GM-CSF, and IL-5. Synthesis of IL-5 by eosinophils was demonstrated by in situ hybridization and immunostaining in a variety of diseases, such as coeliac disease, asthma, hypereosinophilic syndrome, or skin diseases. However, IL-5 synthesis by eosinophils was not shown in Crohn's disease, whereas in other diseases, it was restricted to a subpopulation of eosinophils, suggesting some heterogeneity in cytokine-producing eosinophils. Here, we report that human eosinophils, in addition to the synthesis of IL-5, and Th2 cytokine, can synthesize IFN gamma, a Th1 cytokine, as well as IL-10 and IL-4, known to be mainly produced by Th2 cells. Double immunostaining procedures reveal the coexpression of IL-5, IL-4, and IL-10 by the same eosinophil populations, different from IFN gamma-producing eosinophils. We propose that distinct subpopulations of human eosinophils express Th2 or Th1 cytokines. These results point to the importance of cytokines derived from non T cells in the regulation of the immune response.