Selective Modulation of the Natural Killer Activity of Murine Intestinal Intraepithelial Leucocytes by the Neuropeptide Substance P

Neuropeptides can influence immune effector cell function at both systemic and mucosal immune sites. We examined the ability of substance P (SP) to modulate the natural killer (NK) activity of intestinal intraepithelial leucocytes (IEL). Yac-1 killing by IEL but not splenic cells was increased after either 18 hr preincubation or 6 hr of co-incubation with SP. We also examined the NK activity of IEL and spleen isolated from mice treated with SP in vivo. The selective increase in NK activity of IEL occurred without any demonstrable change in the number or phenotype of the IEL. The IEL responsive to SP in vivo and induced in vivo by SP were both Thy-1- and did not kill the NK insensitive mastocytoma cell line P815. Lastly, we examined the ability of SP to induce the release of interleukin-2 (IL-2) and IL-4 from IEL after 6 and 18 hr of in vitro culture. No increase in the release of these cytokines was observed, suggesting that IL-2 and IL4 are not involved in the local augmentation of IEL NK activity by SP. These observations suggest that SP has a selective stimulatory effect on intestinal activity and may play a role in the regulation of intestinal cell-mediated immunity.