Interleukin 1 beta and phorbol ester induce tumour necrosis factor alpha production in a hepatic cell line (HepG2)

Tumour necrosis factor alpha (TNF alpha) is a pleiotropic cytokine that is produced mainly by monocytes and macrophages. TNF alpha appears to be responsible for many of the inflammatory and necrotic changes seen in malignant or infectious liver diseases. In addition, blood levels of TNF alpha have been reported to be elevated in those with hepatic diseases. Although TNF alpha is synthesized mainly by monocytes and macrophages, its production has recently been found in nonhaemopoietic cells as well. Therefore we have used the human liver cell line HepG2 to test for the inducible production of TNF alpha in hepatic parenchymal cells. No constitutive TNF alpha gene expression was detected by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). However, treatment with the proinflammatory cytokine interleukin 1 beta (IL-1 beta) or phorbol 12-myristate-acetate (PMA) led to a marked increase in TNF alpha mRNA levels. Maximal TNF alpha: mRNA levels were observed after 3-h incubation periods, decreased thereafter and became undetectable after 12 h. The culture supernatant from cells treated with IL-1 beta or PMA contained significant amounts of TNF alpha protein which was immunologically detectable and biologically active. We believe that our report of inducible TNF alpha production in this widely available hepatic cell line adds a valuable tool for understanding TNF alpha gene expression in nonhaematopoietic cells.