Activation of macrophages by neuropeptides

Macrophages play a key role in the initiation and execution of immunoinflammatory responses. Evidence is reviewed which indicates that neuropeptides are capable of up- or down-regulating their state of activation. Substance P, neurokinin A, neurotensin, bombesin, gastrin-releasing peptide, endorphins, enkephalins, somatotropin, and somatostatin elicit various responses in monocytes and macrophages, presumably as a consequence of receptor stimulation. However, formal evidence for the existence of functional surface receptors on these cells is available only for substance P. Activation of macrophages by neuropeptides is yet another example of neuroimmune modulation. These interactions may be involved in the regulation of local immunity in tissues with dense neuropeptidergic innervation and could also contribute to tissue damage under a number of inflammatory conditions.