Human monocyte chemotactic activity of calcitonin and somatostatin related peptides: modulation by chronic peptide treatment

Neuropeptides are common mediators of the nervous and the immune systems. We investigated whether two families of peptides, calcitonin (CT) and somatostatin, possess human monocyte chemotactic activity. CT-related peptides induce a significant chemotactic response, and the potency order is: salmon CT > human CT > CT >> carbo-CT; CT gene-related peptide is completely inactive. This rank potency order differs from that in other systems (e.g. bone and nervous system). The chemotactic response of monocytes obtained from patients chronically treated with either salmon CT or carbo-CT is impaired, thus suggesting a phenomenon of down-regulation of a common receptor on monocytes. While somatostatin-(1-14) is completely inactive on monocyte chemotaxis, the synthetic analog SMS 201995 is extremely potent. Also, in this case the prolonged treatment of patients with SMS 201995 leads to an impaired chemotactic response.