Modulation of the immune system by the autonomic nervous system and its implication in immunological changes after training.

This review examines the role of the autonomic nervous system in the regulation of the immune system to understand the alteration of immunological parameters under the influence of stressors and exercise. Sympathetic innervation in secondary lymphoid organs plays a major role in immune regulation. Catecholamine released from the nerve terminal serves as the major mediator when bound to adrenergic receptors present on immunocompetent cells. Experiments using chemical and surgical denervation, catecholamine knock-out mice, and receptor antagonist and agonists revealed several important points. Sympathetic nerve activity is generally suppressive for the immunocompetent cells in the blood stream except neutrophils. Sympathetic activity facilitates detachment of T cells and NK cells from blood vessels without affecting functional adhesion molecule expression. Th1 cells express more beta 2 adrenergic receptors than Th2 cells, indicating a greater influence of sympathetic activity on Th1 response. Sympathetic action was also shown to regulate the production of chemokines. Taken together, the sympathetic nervous system does not simply suppress the immune system but might help organize the immune response sequentially and spatially by modulating the distribution of immunocompetent cells.