Human eosinophil cationic proteins (ECP and EPX) and their suppressive effects on lymphocyte proliferation.

ECP (eosinophil cationic protein) and EPX (eosinophil protein X) are two highly basic proteins contained in the granules of human eosinophils. In this study, the effect of ECP and EPX upon lymphocyte proliferation in vitro has been investigated. Peripheral blood mononuclear cells from normal donors were cultured in medium containing ECP or EPX at concentrations from 10(-10) to 10(-7) M. 3H-Thymidine incorporation in PHA-blasts or MLR-blasts was dose-dependently inhibited by both ECP and EPX. The effect was irreversible and was not due to cytotoxic damage. The suppressive effect of EPX may involve suppressor cells. The effect of ECP and EPX on lymphocyte proliferation at relevant in vivo concentrations suggests a regulatory role for the eosinophil in immunological reactions.