Serum amyloid A, cytokines, and corticosterone responses in germfree and conventional mice after lipopolysaccharide injection

To determine why germfree mice are less susceptible to lipopolysaccharide ( LPS) than conventional mice, we studied serum levels of serum amyloid A (SA A), tumor necrosis factor (TNF), interleukin 1 (IL-1), IL-6, and corticoste rone in mice after treatment with LPS. A single injection of LPS caused an elevation of SAA, an acute-phase protein in the mouse, in both conventional and germfree IQI mice, and the response was significantly less in germfree mice. LPS-induced elevations of serum TNF, IL-1, and IL-6 levels were also significantly less in germfree mice, while serum corticosterone levels wer e greater in germfree mice than in conventional mice. These results suggest that the lower susceptibility to LPS and a smaller response of SAA elevati on by LPS in germfree mice may result from less elevation in serum of these cytokines in these mice, which are known to mediate the acute phase respon se of SAA. High levels of serum corticosterone in germfree mice may be part ly responsible for the lower responsiveness of these inflammatory cytokines to LPS in these mice.