Investigating the Effects of Typhoid Vaccine on Sleep in Healthy Volunteers

Elevated levels of pro-inflammatory cytokines are implicated in the pathogenesis of major depression. Both clinical and animal studies have shown that pro-inflammatory cytokines can induce a behavioural repertoire of symptoms collectively referred to as 'sickness behaviours,' which include cognitive and mood symptoms, such as depression, anxiety, memory impairment, fatigue, anhedonia and sleep disturbance.

Raised circulating pro-inflammatory cytokines exhibited during chronic medical illness, such as rheumatoid arthritis, are frequently associated with higher rates of co-morbid depression compared to the general population. Medically healthy individuals with major depression have also been shown to have raised pro-inflammatory cytokine levels. Moreover, administration of interferon-α (IFN-α), a recombinant form of inflammatory cytokine that is commonly used as a therapy for hepatitis C virus (HCV) and certain cancers, is well documented to precipitate depression and cognitive impairment in 30-50% of patients. In a previous study in this Department the investigators showed, using magnetic resonance spectroscopy (MRS), that IFN- α increased markers of glutamate activity. This is of particular interest because of the postulated role of glutamate in mood regulation and cognition.

Converging evidence of the link between inflammation and depression has therefore led to the hypothesis that chronic low-grade inflammation could lead to more persistent alterations in neuropsychological function that might be instrumental in the pathogenesis of major depression. However, the mechanisms for this potential modulation of mood and cognitive function remain unclear.

In order to examine the relationship between inflammation and depression, experimental models of inflammation have been developed that involve exogenous administration of cytokines or cytokine-inducers, for example salmonella typhi (typhoid) vaccination. This study will utilise typhoid vaccination as a model of acute inflammatory challenge in healthy volunteers, which has previously been shown to stimulate a mild, non-sickness inducing inflammatory response that significantly increases levels of the pro-inflammatory cytokine, interleukin (IL)-6, in a safe manner without increasing symptoms of illness, body temperature and blood pressure. This model has been shown to elicit a transient depression-like syndrome in healthy volunteers, including a range of behavioural changes such as cognitive dysfunction, fatigue and modulation of subjective ratings of mood. The investigators believe this will serve as a good model to investigate effects of immune activation on sleep.

Sleep electroencephalogram (EEG) recordings will explore the effects of immune activation on sleep, as sleep changes are observed in clinical depression. Healthy volunteers will be recruited for this study, so that the investigators can investigate the effects of inflammatory challenge in participants that do not currently have an inflammatory condition.