Immune cells in the protective tissue that surround the brain are necessary for the regulation of social behaviour in mice, according to a paper published online this week in Nature. The study suggests that dysfunctional immunity may contribute to the impaired neural circuitry underlying the social deficits observed in many neurological and psychiatric disorders.

Altered immune responses have been associated with disorders such as autism and schizophrenia. Although immunity in the peripheral nervous system has previously been shown to influence learning and memory, the interaction between the immune system and the neural circuits that give rise to the social deficits that characterize these disorders is not well understood.

Jonathan Kipnis and colleagues demonstrate that mice deficient in adaptive (acquired) immunity do not show preference for investigating another mouse over an object and exhibit hyper-connectivity between the frontal regions of their brain, reminiscent of patients with autism. The authors were able to rescue these deficits and normalize brain connectivity by repopulating mice with lymphocytes. They find that neurons respond directly to interferon gamma - a substance secreted by immune cells that is predominantly thought to fight pathogens - regulating the activity of neural circuits implicated in social behaviours. Finally, the authors report that this interaction between immunity and social behaviour is also present in rats, zebrafish and fruit flies. They suggest that an anti-viral response may have co-evolved with sociality in higher species and that these pathways could potentially be manipulated by fast-evolving pathogens.