BriefDefinitive Report INTERLEUKIN 5 ENHANCES INTERLEUKIN 2-MEDIATED LYMPHOKINE-ACTIVATED KILLER ACTIVITY BY

After 3-6 d ofin vitro incubation with IL-2, human PBL and mouse splenic lymphocytes become cytotoxic to a variety of tumor cells, including not only NK-sensitive, but also NK-resistant tumor cells (1-3) . These IL-2-dependent lymphocytes consist ofa heterogeneous population ofeffectors (4-6) . They also show non-MHC-restricted cytotoxicity, which has been referred to as the lymphokine-activated killer (LAK) phenomenon (2) . On the other hand, murine IL-5 (mIL-5) was previously described as a T cell-replacing factor (TRF) (7, 8) and as a B cell growth factor II (9) based on its induction of proliferation and Ig secretion by activated B cells . This lymphokine has been shown to exert several other effects, including the induction of growth and differentiation of eosinophils from bone marrow stem cells (10), the induction of differentiation of peanut agglutinin-positive (PNA+) thymocytes into CTL (11), and the induction of mIL-2-R expression on both splenic B cells and PNA+ thymocytes (12, 13) . In this study, we examined the effect of mIL-5 on the in vitro induction of LAK activity as a basic study for modified adoptive immunotherapy.