Regulation of peripheral blood mononuclear cell responses to Dermatophagoides farinae by substance P in patients with atopic dermatitis

Abstract Neuropeptides mediate stress-induced cutaneous inflammation such as atopic dermatitis. The effect of substance P on proliferation and cytokine mRNA expression of peripheral blood mononuclear cells in response to Dermatophagoides farinae (Der f) was studied in atopic dermatitis patients with positive RAST scores to Der f. Upon stimulation with Der f peripheral blood mononuclear cells from patients proliferated in a B7-dependent (CD80- and CD86-dependent) manner, while those from the patients with negative scores, nonatopic eczematous dermatitis patients or normal individuals, did not. Based on the reactivity of normal individuals, atopic dermatitis patients with a stimulation index greater than 1.8 were tentatively defined as high responders, who comprised two-thirds of the patients. Proliferation in high responders was associated with upregulation of IL-2 mRNA expression and induction of IL-5 mRNA expression. Substance P at 10^–10 to 10^–8 M promoted the Der f-induced proliferation when added at the start of culture and upregulated IL-10 mRNA expression while downregulating IL-5 mRNA expression. Our results suggest that substance P modifies immune responses of atopic T cells to Der f by promoting proliferation and altering cytokine profiles, and thus modulates the clinical manifestations of atopic dermatitis.