Trace Amine-Associated Receptors in the Cellular Immune System

Trace amine-associated receptors (TAARs) are members of rhodopsin-like family A of G-protein-coupled receptors. TAARs were initially found in the brain, and specifically recognize certain "trace" amines, some of which can be found in the plasma and in the central nervous system at low pico- to nanomolar concentrations. TAAR have been identified in sensory neurons of the olfactory epithelium, where they may detect volatile amines such as odorants, pheromones, or kairomones, at least in rodents, but also in fish. Recently, certain TAAR have been found to be specifically expressed in different types of peripheral blood leukocytes, mediating the potent activation of a variety of immune cell functions by trace amounts of certain amines. This chapter reviews evidence for the expression of TAAR in blood leukocytes, their activation by trace amounts of TAAR agonists, and discusses their potential relevance for biogenic amine-related immune cell functions.