The purpose of the current study was to characterize lymphokine-activated killer (LAK) activity induced with IL-4/B cell stimulatory factor-1 and to compare IL-4-induced LAK activity with IL-2-induced LAK activity. Culture of murine lymphocytes with high concentrations of IL-4 induced nonspecific lytic activity against a wide variety of tumors. Lytic activity induced by IL-4 increased with increasing concentrations of IL-4 over the range of 1.0 to 25 ng/ml. The kinetics of LAK induction by IL-4 and IL-2 were similar; however, IL-4 was less effective than IL-2 in maintaining lytic activity for longer culture periods and provided lower viable cell yields than did IL-2. Similar to IL-2, IL-4 induced blastogenesis and the generation of large granular lymphocytes, all LAK activity observed was exclusively associated with the large granular lymphocyte fraction, and the cytolytic effector cells were heterogeneous in regards to cell surface phenotype. The majority of IL-4-induced lytic activity was associated with mutually exclusive NK-like (i.e., NK-1.1+ Lyt-2-) and T cell-like (i.e., NK-1.1- Lyt-2+) LAK cells. The precursors for each subset were distinct and expressed the asialo-GM1+ Lyt-2- and the asialo-GM1+ Lyt-2+ phenotypes, respectively. Although IL-4-induced LAK effector cells were morphologically and phenotypically similar to IL-2-induced LAK cells, IL-2 generated equivalent numbers of T cell-like and NK-like LAK cells, whereas IL-4 generated 3.5-fold more T cell-like LAK cells than NK-like LAK cells. It might eventually be possible to exploit the preferential activation of T cell-like LAK by IL-4 for therapeutic advantage.

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