Inhibition of Growth by Pro-Inflammatory Cytokines: An Integrated View

In response to antigenic stimuli, a variety of cells, including activated macrophages, secrete cytokines that are responsible for altering the host's metabolism. Three of these cytokines (tumor necrosis factor alpha [TNF-α], interleukin-1 [IL-1], and interleukin-6 [IL-6]) have profound behavioral, neuroendocrine, and metabolic effects. There is evidence that cytokines and their cognate receptors are present in the neuroendocrine system and brain. Moreover, in laboratory animal species, IL-1, IL-6, and TNF-α have been found to modulate intermediary metabolism of carbohydrate, fat, and protein substrates, regulate hypothalamic-pituitary outflow, and act in the brain to reduce food intake. Finally, many of the systemic acute-phase responses to inflammatory stimuli such as lipopolysaccharide are inhibited by treatment with cytokine receptor antagonists. In short, many findings converge to suggest that a major component of the growth inhibition observed in immunologically challenged animals is mediated by pro-inflammatory cytokines. The goal of this article is to provide an integrated view of how cytokines act systemically on disparate tissues to alter growth.