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Characteristics of a Cytotoxin ("Lymphotoxin") Produced by Stimulation of Human Lymphoid Tissue¹

From the Department of Medicine, UCLA School of Medicine, Los Angeles, California 90024

Abstract

Stimulated lymphocytes derived from human peripheral blood, tonsils, adenoids and thoracic duct lymph elaborate a cytotoxic activity (cytotoxin, lymphotoxin) which causes release of ¹⁴C-protein or ⁵¹Cr from prelabeled L cells or HeLa cells. Mouse mastocytoma and Ewing's sarcoma cells, as well as red blood cells and lymphocytes of several species, are not susceptible to the cytotoxin and none of the cells tested, including L cells, absorb or inactivate the cytotoxin. Inhibition of L cell proliferation by mitomycin C or colchicine does not alter susceptibility to cytotoxin but cytotoxin-induced release of ⁵¹Cr is increased by irradiation of L cells.

The kinetics of action of cytotoxin are complicated by a lag phase which is temperature sensitive as opposed to the rate of ⁵¹Cr release itself which is similar at different temperatures after the lag phase is completed.

Characteristics of the cytotoxic activity, including its heat lability, inhibition by certain drugs, precipitation with (NH₄)₂SO₄, molecular size, and polydisperse chromatographic pattern, are similar regardless of the lymphocyte source. Most of the cytotoxic activity induced by stimulation with purified phytohemagglutinin P, concanavalin A, pokeweed mitogen, and purified protein derivative tuberculin (PPD) is precipitated at 37% to 50% (NH₄)₂SO₄ saturation. The cytotoxin elaborated by PPD stimulation of sensitized lymphocytes is significantly more heat labile than that induced by mitogen.

A variety of putative substrates for the cytotoxin do not inhibit its action. Serum of some normal rabbits contains a potent inhibitor.

Footnotes

¹ This work was supported by National Institutes of Health Grant GM 15759.