U937 cells stimulated with opsonised zymozan particles provide a convenient laboratory source of tumour necrosis factor alpha.

The U937 cell line has been shown to generate tumour necrosis factor alpha (TNF-alpha) in response to soluble stimuli such as PMA and LPS, but only after treatment with GM-CSF. We report here the generation of TNF-alpha from U937 cells following phagocytosis of opsonised zymozan particles without the need for pre-treatment with GM-CSF. The release of TNF-alpha from U937 cells was demonstrated by a specific radioimmunoassay, L929 cell killing and neutrophil 'priming'. The biological activities in the cell supernatant were inhibited by TNF-alpha antiserum. Phagocytosis was required for TNF-alpha production. Non-opsonised zymozan or latex particles which were not phagocytosed or pretreatment with cytochalasin B, which inhibited phagocytosis of opsonised zymozan particles, all failed to trigger TNF-alpha production. Phagocytosis failed to trigger detectable IL-1 generation, and production of IL-6 was insufficient to produce biological effects on neutrophils. The U937 supernatant thus provides a source of human TNF-alpha which can be generated conveniently and cheaply for experimental investigations.