Animal studies show that cytokine mediated illnesses — for example infectious, autoimmune and neurodegenerative diseases — are associated with behavioural changes. But the underlying mechanisms in humans have not yet been established. In the May Archives of General Psychiatry Abraham Reichenberg and colleagues from the Hebrew University of Jerusalem, Israel show that in humans the level of circulating cytokines may influence not only emotional state but cognitive function as well.
Reichenberg et al investigated the effects of low-dose endotoxemia, a well-established and safe model of host-defence activation in 20 healthy male volunteers. In a double-blind, crossover study, the volunteers completed psychological questionnaires and neuropsychological tests at 1, 3 and 9 hours after intravenous injection of Salmonella abortus equi endotoxin (0.8 ng/kg) or saline. Endotoxin caused a mild increase in rectal temperature (0.5°C) and increased the circulating levels of tumor necrosis factor, soluble TNF receptors, interleukin-6, IL-1 receptor antagonist and cortisol. Positive correlations were found between cytokine secretion and endotoxin-induced anxiety, depressed mood and decreases in memory performance (Arch Gen Psychiatry 2001, 58:445-452).
These results may have implications for the development of new psychopharmacological approaches that should target the negative psychological effects of cytokines in various medical conditions.