Neuroimmunology beyond the CNS: Nerve-macrophage interactions in peripheral tissues

Macrophages are now recognised to be highly heterogeneous, with diverse ontogenies, anatomical locations and characteristics, all of which inform their function. Nerve-associated macrophage subpopulations have been found to exist across tissues, and whilst they appear to have roles in neuronal maintenance and repair, their function is still being elucidated. Although nerve-associated macrophage functions in the Central Nervous System have taken centre-stage, nerve-associated macrophages also interact with peripheral nerves and this field remains relatively understudied. This review discusses recent studies into nerve-associated macrophages across peripheral tissues. These studies identify populations of nerve-associated macrophages in many peripheral tissues, and reveal elegant neuroimmune communication pathways which coordinate functions from infection defence and anti-inflammatory actions to neuronal maintenance for homeostatic tissue function and nerve repair. We highlight nerve-associated macrophage interactions with nerves in peripheral tissues as a rapidly evolving field which could revolutionise our understanding of macrophage function in both homeostasis and disease.