Fever and Survival in Aged Mice After Endotoxin Challenge

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Abstract
Male CS7BL/6 mice of 12,19, and 24 months of age received injections of low (25 μg 100 g−1 body weight) or high (5O μg 100 g−1 body weight) doses of Salmonella typhosa endotoxin and were exposed to ambient temperatures below (24 °C) or within (30 °C) the thermoneutral zone. Old mice (19 and 24 months) developed initial fevers followed by hypothermia in response to endotoxin challenge at 24 °C, irrespective of dose; 12-month-old-mice became hypothermic at 24 °C following injection of the high dose of endotoxin only. At 30 ° C, 12- and 19-month-old mice developed and maintained fever over 4 hr in response to endotoxin compared with the 24-month-old mice who were unable to maintain fevers. Logistic regression analysis showed that age, ambient temperature, and body temperature responses were significant predictors of survival outcome in endotoxin-treated mice; of these, age and ambient temperature had the strongest effects.