Effect of Age on Fever Response to Recombinant Interleukin-6 in a Murine Model

BACKGROUND: A blunted or absent fever response to infection may occur in elderly people. Fever is mediated by endogenously produced molecules of leukocytes. The best studied of these molecules is interleukin-1 (IL-1). However, interleukin-6 (IL-6) is also known to possess the biological properties of pyrogenic cytokines. In this study, we assessed the influence of age on the febrile response to recombinant IL-6 (rIL-6) using a well-defined murine model. METHODS: Balb/c male mice were injected intravenously and intraperitoneally with varying doses of rIL-6. Control mice received pyrogen-free phosphate buffered saline. Temperatures were measured rectally at baseline and at 10-minute intervals for 120 minutes post-injection using a thermistor probe. Stable baseline temperatures were first determined, and post-injection temperatures were recorded every 10 minutes for up to 120 minutes. RESULTS: A dose-response correlation was found between the amount of the injected rIL-6 and the mean temperature changes in both young and old mice. The mean temperature changes for both young and old mice were higher following a 25 ng dose compared to a 12.5 ng dose of rIL-6 injected intravenously, and, likewise, following a 500 ng dose compared to a 250 ng dose of rIL-6 injected intraperitoneally. A significant delay in the peak temperature response was seen for both young and old mice when comparing intraperitoneal injections to intravenous injections. However, control mice showed no changes. CONCLUSIONS: Our findings confirm that IL-6 has a role in the pathogenesis of fever and that aging alters the febrile response to rIL-6.