Decoding the Dialogue: Immunity and central nervous system interactions in neurodegenerative diseases

This review article aims to discuss neuroimmune interactions by emphasizing the role of central and peripheral immunities in central nervous system (CNS) protection and function, as well as how abnormalities in this relationship may be implicated in the genesis of neurodegenerative diseases (NDDs). Immune elements that play roles within the CNS both during stable and infectious states are described. Innate CNS immunity is explored as a distinct entity comprised of the brain blood barrier, CNS parenchyma, and resident immune cells-microglia and astrocytes, whose roles in antigen recognition and clearance and neuromodulation are further enumerated. Due to the inability of the CNS to independently initiate an adaptive immune response, the necessary recruitment and regulation of elements from the peripheral immune system (PIS) are described in a process that, in chief, utilizes resident antigen-presenting cells to prime naïve T-cells, which later enter the CNS through areas of access to the cerebrospinal fluid. The previous modes of interaction especially enable microglia, astrocytes, and T-cells to play part in neurodevelopment and plasticity, and the proposed mechanisms by which they participate in synaptic pruning, neurogenesis, and memory are examined. In addition to its protective role, the PIS has also been shown to play a regulatory role in the CNS, where it drives responses that optimize immune function, such as fever and sickness behavior. Due to the high level of involvement of the immune system within the CNS, dysregulations of the immune system are thought to be implicated in numerous NDD pathogeneses, where neuroinflammation both causes and is caused by immune reactions. Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis are particularly discussed.