Diet-induced weight gain produces a graded increase in behavioral responses to an acute immune challenge

Sickness behaviors and fever during infection constitute an adaptive and tightly regulated mechanism designed to efficiently clear the invading pathogen from the body. Recent literature has demonstrated that changes in energy status can profoundly affect the fever response to an acute immune challenge. The purpose of the present study was to investigate whether the exacerbating effect of diet induced obesity (DIO) on the LPS-induced fever response demonstrated previously would generalize to other sickness behaviors and, further, whether incremental changes in body weight would influence these responses. Results showed that DIO male Wistar rats exhibited a higher number of sickness symptoms for a longer period after lipopolysaccharide (LPS) injection (100μg/kg) than lean rats. Similarly, they showed a more prolonged fever and a delayed recovery from LPS-induced suppression of social interaction. No difference in locomotor activity was observed between obese and lean groups. Comparisons among groups that varied in body weight showed that an 11% increase in body weight was sufficient to increase the number and duration of sickness symptoms displayed after an LPS-injection and that the severity of sickness symptoms increased with increasing body weight. Together these data suggest that DIO can have profound effects on multiple behavioral responses to an acute immune challenge placing obese organisms at higher risk of the consequences of prolonged inflammation.