Aberrant acute-phase response in aged interleukin-6 knockout mice

This study was designed to determine whether the acute-phase response in aged mice is altered by interleukin (IL) 6 deficiency. Young and aged wild-type (WT) and IL-6 knockout (KO) BALB/C female mice were injected with lipopolysaccharide (LPS; 1.5 mu g/g body weight). After 24 h, aged IL-6 KO mice had an improved survival when compared with aged WT mice. Serum levels of IL-6 in aged WT animals given LIPS were determined and, as expected, were significantly higher when compared with young LPS-treated WTanimals (P < 0.05). Serum levels of the acute-phase protein, serum amyloid A, were 50% lower in aged LPS-treated IL-6 KO mice relative to aged WT mice given LPS (P < 0.001). In contrast, the induction of LPS-binding protein was not affected by age or IL-6 deficiency in LPS-treated animals. Circulating levels of corticosterone were markedly reduced in aged LIPS-treated IL-6 KO mice relative to aged WT mice given LIPS. These data indicate that IL-6 is an important contributor to the outcome of the acute-phase response of aged individuals challenged with endotoxin. We conclude that the absence of IL-6, a cytokine that contributes to the elevated basal proinflammatory state observed in aging, can improve the ability of aged mice to withstand an otherwise lethal challenge of bacterial endotoxin.