Close encounters of the monoamine kind: immune cells betray their nervous disposition.

Here we review the evidence for immune cells expressing multiple components of the serotonergic and dopaminergic systems that are more commonly associated with the central nervous system (CNS). We discuss where and how peripheral encounters with these biogenic monoamines occur and posit reasons as to why the immune system would wish to deploy these pathways. A full taxonomy of serotonergic and dopaminergic constituents and their workings in component cells of the immune system should facilitate the formulation of novel therapeutic approaches in diseases characterized by immune dysfunction and potentially provide a range of surrogate peripheral markers for registering and monitoring disturbances within the CNS.