Noradrenergic and peptidergic innervation of lymphoid organs.

It now is evident that extensive neural-immune anatomical connections exist between the nervous and immune systems, with close contacts of nerves with lymphocytes and macrophages. The presence of receptors for catecholamines and neuropeptides on these cells, coupled with functional evidence that these neural signals can modulate immune responses, brings these putative neurotransmitters to the forefront as a class of immunomodulatory molecules that can be investigated for possible benefit of disorders resulting from enhanced or suppressed activity of specific aspects of immune function. Furthermore, feedback from the immune system (cytokines) can act locally on lymphoid organ innervation to modulate transmitter release, and can act on the central nervous system via the vagus nerve to alter central pathways relevant to the immune system. It certainly is very clear that extensive bidirectional interactions occur between the nervous and immune systems, and that one system cannot be considered functionally without taking into account the state of activity of the other system.