In vitro lymphocyte cytotoxicity : I. Evidence of multiple cytotoxic molecules secreted by mitogen activated human lymphoid cells in vitro

Abstract

Multiple families of cytotoxic molecules [Lymphotoxin (LT)] have been identified in phytohemagglutinin (PHA-P) activated human lymphocyte supernatants and lymphocyte homogenates, using gel filtration chromatography on Sephadex G-150. These macromolecules have molecular weights of 80–90,000, 50,000, and 10–15,000 daltons and have been termed LT 2, LT 2 and LT 3, respectively. They are secreted by cells from a variety of lympboid tissues, i. e., tonsil, adenoid, and peripheral blood. The kinetics of appearance of the cytotoxins indicate that all three are present within 16 hr after lymphocyte activation. However, while LT 1 and LT 2 persist in these cultures through day 5, LT 3 is not detectable after day 3. These molecules can also be detected when either PHA or concanavalin A are employed as the stimulating agent. Moreover, the relative amounts of LT 1, LT 2 and LT 3 activity in a given supernatant vary dramatically from culture to culture. Extracellular levels of LT accumulate and peak by 4 to 5 days in culture, however, intracellular levels of LT reach a maximum on day 3 and decrease to very low levels on day 5. Mitogen-stimulated lymphocytes at 3 days contain intracellular levels of LT which are several logs higher than that detectable in unstimulated cells. This observation suggests that both the biosynthesis and secretion of lymphotoxin is governed by a regulatory control process(es).