Quantification of TNF-alpha and IL-6 bioactivity in response to lipopolysaccharide in the degu (Octodon degus)

The proinflammatory cytokines TNF-alpha and IL-6 are important inflammatory mediators that may be regulated by circadian rhythms. However, the production and detection of these cytokines have not been examined in the degu, a diurnal species used in some studies of circadian rhythms. In this study, we used bioassays to attempt to measure tumor necrosis factor (TNF-alpha) and interleukin 6 (IL-6) levels in degus exposed to an inflammatory stimulus, lipopolysaccharide (LPS). In an in vitro study, whole blood was incubated with LPS. After 6 and 24 h of LPS stimulation, TNF-alpha levels were substantially increased. However, IL-6 was not found in any of the samples. In an in vivo study, LPS was given to degus intraperitoneally. Similar to responses seen in other species, LPS stimulation resulted in marked neutrophil recruitment into the peritoneal space but not the alveolar space. TNF-alpha was present in large amounts in plasma and/or peritoneal lavage fluid. Again, IL-6 was not detectable with the bioassay. These findings suggest that degus do not produce IL-6, that they produce IL-6 in extremely small amounts, or that the bioassay is unable to detect IL-6 from degus. In conclusion, using well-established models of acute inflammation, this study demonstrated that TNF-alpha, but not IL-6, could be detected in plasma and peritoneal lavage fluids from degus with standard bioassays used for cytokine detection in other species.