Altered interleukin-1 and tumor necrosis factor production and secretion during pyrogenic tolerance to LPS in rabbits

Rabbits were injected intravenously with 10 μg/kg of endotoxin [lipopolysaccharide (LPS)] on days 0, 1, and 7, and rectal temperatures were monitored. The febrile responses were compared with circulating levels of interleukin-1β (IL-1β) and tumor necrosis factor (TNF) and in vitro synthesis of these cytokines by peripheral blood mononuclear cells (PBMC) isolated just before the injection of LPS. Fever after the first LPS injection was biphasic on day 0, attenuated and monophasic after the second LPS injection on day 1, and augmented after third injection of LPS on day 7. On day 1, circulating TNF and IL-1β levels were significantly (P < 0.05) decreased compared with those on days 0 and 7. Similarly, TNF and IL-1β synthesis by LPS-stimulated PBMC were significantly reduced on day 1. On day 7, cellular synthesis and secretion of IL-1β were significantly increased compared with that on day 0. A significant positive correlation was observed between fever index and total in vitro IL-1β synthesis by LPS-stimulated PBMC (r = 0.866, P = 0.001). These data demonstrate that pyrogenic tolerance in the rabbit after a single LPS injection is associated with decreased circulating IL-1β and TNF levels as well as decreased production of these cytokines in vitro. In addition, the pyrogenic hyperresponsiveness to LPS after 7 days is associated with increased synthesis and secretion of IL-1β from PBMC in vitro.