Immunity, Immunosenescence, Brain and Cognitive/Mental Health

The brain was once considered as an immunoprivileged organ, mainly due to a tight blood-brain barrier. However, recent research shows that immune cells are participating in the surveillance, homeostasis and functioning of the brain. These typically also include brain-resident immune cells such as microgliaMicroglia, astrocytesAstrocyte and specialised T cells. This interaction between the brain and immunity assures a harmonized functioning. However, there could occur a dysregulation following various insults, including infectionsInfection, trauma, toxic substances, dysbiosis and ischemia. These challenges lead to neuroinflammationNeuroinflammation which would serve to maintain the relatively normal functioning of the brain. AgeingAgeing is generally associated with immune changes including low-grade inflammatory processes. These ageingAgeing-associated perturbations conjugated to the environmental challenges may lead to dysregulation of the brain homeostasis e.g. by generating misfolded proteins, resulting in uncontrolled neuroinflammationNeuroinflammation. The prototypic diseases related to these ageingAgeing-related processes are Alzheimer’s diseaseAlzheimer's disease (AD), Parkinson’s disease and amyotrophic lateral sclerosis. However, some other inflammatory disorders such as multiple sclerosisMultiple sclerosis, and mental healthMental health diseases (mood disordersMood disorders) such as depression and bipolar disease may remotely relate to these age-related immune processes. In this chapter we will describe how the immune responseImmune response is changing with ageingAgeing in the brain and how it impacts the various neurodegenerativeNeurodegenerative diseases and mental healthMental health problems.