Systemic endotoxemia induces integrated sickness physiology in female BALB/c mice

Sickness is an organismal response to inflammation, yet its immune, metabolic, neural, and behavioral components are often studied separately and predominantly in male C57BL/6 mice. In this study, we characterized these responses to systemic lipopolysaccharide (LPS) in female BALB/c mice. Mice received intraperitoneal LPS at moderate concentrations and outcomes were assessed during the acute and resolving phases of endotoxemia. LPS caused rapid disappearance of resident peritoneal macrophages, followed by neutrophil accumulation and increased circulating TNF- and IL-6. In the liver, LPS induced inflammatory, acute-phase, and anti-inflammatory transcripts while suppressing genes involved in lipid, cholesterol, and xenobiotic metabolism. Hepatic glutathione was reduced, whereas total superoxide dismutase activity was unchanged. These peripheral responses were followed by transient hypothermia, reduced food intake, and body weight loss. Regional brain mapping showed increased c-Fos labeling in the area postrema, nucleus of the solitary tract, external lateral parabrachial nucleus, paraventricular nucleus of the hypothalamus, and arcuate nucleus. In parallel, LPS selectively promoted IBA1-positive area in the median eminence and arcuate nucleus, whereas several other regions showed no changes, indicating that neuronal and microglial responses are regionally distinct. Behaviorally, LPS reduced locomotion and exploration, increased freezing, and increased forced-swim immobility. Changes in spatial exploration were most pronounced during the acute phase, whereas locomotor suppression and passive stress-coping persisted longer and varied in magnitude with the timing of inflammatory challenge. Together, these findings show that systemic LPS produces a coordinated sickness state in female BALB/c mice that links peripheral inflammation and hepatic metabolic and redox changes with region-specific neuronal and microglial responses, altered thermoregulation and feeding, and behavioral suppression.