Inhibition of natural killer activity by calcitonin gene-related peptide

The effect of calcitonin gene-related peptide (CGRP) on natural killer (NK) cell activity in spleen cells from Balb/c mice and nude mice was studied. CGRP dose-dependently (10(-9) to 10(-7) M) inhibited NK activity of spleen cells from both strains of mice. This inhibitory effect was observed at the effector to target ratios of 12.5:1 to 100:1. Maximum inhibition by 10(-7) M CGRP was about 60%. The inhibition of NK activity by CGRP was also observed in anti-Thy 1.2 plus complement treated Balb/c spleen cells. Furthermore, when cells were treated with 10(-9) to 10(-7) M CGRP the concentration of intracellular cyclic AMP increased in spleen cells of nude mice. The characteristics of these cells were similar to those of NK cells, (1) being petri dish and nylon wool nonadherent, (2) expressing asialo GM1 antigen, and (3) lacking readily detectable Thy 1 antigen and immunoglobulin. In addition, the intravenous injection of asialo GM1 completely abolished NK activity in spleen cells from nude mice and the increase in intracellular cyclic AMP in spleen cells by CGRP was less in spleen cells from mice given an anti-asialo GM1 injection. Our present study suggests that CGRP inhibits NK cell activity by increasing the intracellular cyclic AMP concentration. CGRP may be implicated in the regulation of NK function.