Interleukin 2-dependent T cell line acquires responsiveness to phorbol myristate acetate and lipopolysaccharide in the course of long-term culture.

We have observed that CT6 cell line, a murine interleukin 2 (IL 2)-dependent T cell line, was highly responsive to phorbol myristate acetate (PMA) and to a lesser extent but significantly responsive to lipopolysaccharide (LPS) in the short-term proliferation assay. In contrast, two other murine IL 2-dependent cell lines, CTLL-2 and NK clone 7, were totally unresponsive to these stimulants. Even when CT6 was recloned by a limiting dilution, no unresponsive clone to PMA was obtained, whereas several clones unresponsive to LPS were obtained. PMA, unlike to IL 2, could not support a long-term culture of CT6. There are no differences between CT6 and CTLL-2 except that the former possessed asialo GM1 while the latter lacked it. Though it is unknown whether this difference is involved in the mechanism of the response of CT6 to PMA or LPS, these data give caution to us against the use of CT6 for the determination of IL 2 activity contaminated with PMA and LPS.