Neuropeptide modulation of the immune response in gut associated lymphoid tissue

The neuropeptides vasoactive intestinal peptide (VIP), substance P, and somatostatin are found in high concentrations in both the central nervous system and the gastrointestinal tract. Specific high affinity receptors for VIP, substance P and somatostatin have been identified on both human and murine lymphocytes, suggesting a role for each of these neuropeptides in a neuroimmune axis. These peptides may be important modulators of mucosal immunity regulating lymphocyte proliferation and trafficking in gut associated lymphoid tissue, synthesis of IgA, and histamine release. Somatostatin antagonism of both VIP and substance P effects has been observed in the immune system. Though the mechanisms by which these neuropeptides modulate immune function have not been completely delineated, current evidence supports the hypothesis that VIP modulates immune function via cAMP dependent pathways while substance P regulation of the immune response involves phospholipid metabolism. Somatostatin inhibition of both cAMP dependent and phospholipid dependent effects has been documented in endocrine tissues. Delineation of the role of these peptide-peptide interactions in modulation of the immune response promises to be a fruitful area for further investigation.