Sickness and the brain

The brain was once believed to be immune privileged, sequestered from peripheral inflammatory signals and pathogens, but it is now clear that bidirectional communication between the immune and nervous systems exists, serving as an integral part of animal physiology and behavior that shapes health and disease. In peripheral tissues, such as the gut, skin, and lungs, sensory neurons and tissue-resident immune cells communicate via soluble signals to fight infection. The field of cancer immunology has been bolstered by the discovery of numerous interactions between the nervous system and immune surveillance of cancer that have significant implications for human health. Similarly, the landscape of immune cells in the brain continues to expand and reveal new interactions with non-neuronal as well as neuronal cells that influence development, aging, and importantly, animal behavior. In this primer, we focus on sickness behavior as a prototypical example of reciprocal communication between the brain and body.