Inhibition of the induction of delayed-type and contact hypersensitivity by calcitonin gene-related peptide.

Calcitonin gene-related peptide (CGRP)-containing nerves are frequently associated anatomically with epidermal Langerhans cells (LC), and LC Ag-presenting function is down-regulated by CGRP. To investigate possible regulation of cutaneous immunity by CGRP, we examined its effect on the induction of delayed-type hypersensitivity (DTH) and contact hypersensitivity (CHS). A system of immunity to the murine spindle cell tumor S1509a (H-2a) was employed to examine induction of DTH by LC. This system requires exposure of epidermal cells (EC) to GM-CSF for induction of substantial immunity. EC were prepared from CAF1 mice (H-2a/d) and Thy-1+ cells deleted. EC were exposed for 16 h to GM-CSF with or without CGRP. EC were then pulsed with tumor-associated Ags (TAA), washed, and injected s.c. into mice three times at 7-day intervals for immunization. Mice were challenged for a DTH response by injection of a hind footpad with TAA-pulsed EC, and 24-h footpad swelling assessed. Exposure of EC to CGRP significantly inhibited induction of DTH. To examine the effect of CGRP administered in vivo on induction of immunity, 530 pmol of CGRP or diluent alone was injected intradermally into the dorsum of the left ear of naive mice 8 h and 3 h before epicutaneous application of a hapten at the injected site. Mice were challenged on the right ear 7 days later and 24 h ear swelling was assessed. CGRP significantly inhibited the induction of CHS whereas calcitonin had no effect. Furthermore, when hapten was applied at a site distant from CGRP administration, no inhibition of CHS was observed, suggesting that the effect of CGRP is local. These data support the concept that CGRP may be an endogenous regulator of immune function and also suggest the possibility that CGRP or its analogues administered in vivo might have therapeutic utility as immunomodulators.