During infection, inflammation, immune responses, and neoplastic growth, various cytokines are produced affecting both susceptibility to and protection from cellular death. We have studied the protective effect of pretreatment of the L929 fibroblast cell line with interleukin 1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha (TNF-alpha), or transforming growth factor beta 1 (TGF-beta) on subsequent TNF/actinomycin D-induced cytotoxicity. The protective effects of these cytokines on TNF cytotoxicity were time and concentration dependent. TGF-beta was the most effective cytokine, followed by TNF, IL-1 beta, and IL-6. Activators of protein kinase C also afforded protection, and TGF-beta acted synergistically with either phorbol 12-myristate 13-acetate or the calcium ionophore A-23187. TGF-beta-induced protection against TNF was observed in cells subjected to prolonged treatment with phorbol 12-myristate 13-acetate. Cells pretreated with prostaglandin E2 or cholera toxin amplified the sensitivity to TNF and inhibited TGF-beta-mediated resistance, whereas indomethacin enhanced the protective effect of TGF-beta. Cells cultured in the presence of IL-1 beta, IL-6, TNF-alpha, or TGF-beta for 6 h inhibited DNA synthesis, and this was associated with concomitant growth arrest in the G1 phase of the cell cycle. On the other hand, prostaglandin E2 or cholera toxin stimulated the progression of cells from G1 toward G2 + M which was associated with increased TNF sensitivity. We conclude that these cytokines protect against death by arresting growth in the G1 phase of the cell cycle.