TNF-beta (lymphotoxin) strongly upregulates TNF-alpha gene expression in human peripheral blood lymphocytes.

We investigated whether TNF-beta could induce or modulate TNF-alpha gene expression in human peripheral blood lymphocytes. For these experiments, lymphocytes were cultured in serum-free medium for 48 hours with human recombinant TNF-beta in the presence or absence of human recombinant IL-2. At the end of the culture period, total cellular RNA was isolated and probed for TNF-alpha mRNA using an S1 nuclease protection assay. TNF-beta alone was unable to induce lymphocyte TNF-alpha mRNA. However, when TNF-beta was used in combination with IL-2 an 8- to 12-fold increase in TNF-alpha mRNA compared to lymphocytes activated in IL-2 alone was observed. Secreted TNF-alpha was measured in the culture supernatants by TNF-alpha specific ELISA. Consistent with the results of mRNA analysis, TNF-beta alone did stimulate TNF-alpha secretion, but lymphocytes activated with TNF-beta/IL-2 demonstrated a 3- to 10-fold increase in secreted TNF-alpha over that induced by IL-2 alone. These experiments demonstrate that TNF-beta can participate in the upregulation of TNF-alpha gene expression in lymphocytes and suggest that cellular dysregulations involving autocrine TNF production may be exacerbated by this positive feedback pathway.