Calcitonin gene-related peptide is chemotactic for human T lymphocytes

Certain neuropeptides, such as CGRP, are associated with C-type nerve fibers in the skin and are known to be proinflammatory mediators. Because of their probable role in various cutaneous diseases, we investigated the effect of alpha- and beta-CGRP on human leukocyte migration in a 48-well microchemotaxis chamber using a 5-microns-pore filter. Elutriated peripheral blood leukocytes (enriched 80-90% for CD3+ and 10-20% for CD20+ lymphocytes) were added to the upper wells, and CGRP to the lower ones in a dose range of 10(-19)-10(-5) M; both were diluted in RPMI medium containing 0.05% fetal calf serum. The chamber was incubated at 37 degrees C for 2.5 hours, and the filter was washed and stained. The mean number of cells migrating through the filter was calculated for quadruplicate wells in each treatment group. Chemotactic activity was expressed as a migration index (MI = number of cells responding to CGRP/media control). Both alpha- and beta-CGRP were optimally chemotactic for leukocytes at approximately 50 pM, with a mean migration index of 11.5 for filter-adherent cells (n = 13 experiments); migration due to chemokinesis was minimal, as measured by checkerboard analysis. Almost all leukocytes that responded to CGRP were T cells (TCs), and the CD4 to CD8 ratio was similar to that of the input population; B cells were not observed. CGRP-induced migration appears to be a specific receptor-mediated event, as pretreating the cells with CGRP resulted in significant down-regulation of their chemotactic response to CGRP, but not to interleukin-1 alpha. Our data suggest that the release of CGRP from free nerve endings near the dermal-epidermal junction could influence cutaneous TC trafficking. As neuropeptides exacerbate (possibly initiate) the inflammatory process, they are likely to be important pharmacological targets in dermatological disorders.