Induction and characterization of lymphotoxins from tumor promoter-synergized, lectin-stimulated human lymphocytes in vitro.

The tumor promoters mezerein and phorbol myristate acetate, and the phorbol diesters phorbol diacetate, phorbol dibenzoate, and phorbol didecanoate synergistically enhanced the production of lymphotoxin (LT) by phytohemagglutinin-stimulated human peripheral blood or tonsil and adenoid lymphocytes. LT production was elevated 2-20-fold, depending on such parameters as the nature of the promoter and dose, the lectin dose, and the lymphocyte source. The increased LT levels were primarily due to enhanced production of the alpha-light (alpha L) class of LT. The alpha L-class obtained from supernatants from promoter-synergized, lectin-stimulated lymphocyte cultures was compared with the alpha L from lectin-stimulated cultures. They were indistinguishable by molecular sieving on Ultrogel AcA44, were both composed primarily of the alpha 2-subclass as determined by ion-exchange chromatography on DEAE-Sepharose, and were immunologically cross-reactive. Lectin-affinity chromatography on concanavalin A-Sepharose and on lentil-lectin--Sepharose revealed that both alpha L preparations were dominated by components with affinity for these matrices. Affinity chromatography on alkyl sorbents also indicated very similar hydrophobicities. Chromatofocusing of the alpha L preparations demonstrated a comparable pattern of isoelectric points. Thus, the use of these drugs in lectin-stimulated human lymphocyte cultures provides an effective means for significantly increasing the yield of alpha L-LT suitable for biochemical purification and analysis, and biological testing in vitro.