Substance P is diminished and vasoactive intestinal peptide is augmented in psoriatic lesions and these peptides exert disparate effects on the proliferation of cultured human keratinocytes. - Pincelli,C.; Fantini,F.; Romualdi,P.; Sevignani,C.; Lesa,G.; Benassi,L.; Giannetti,A. (J Invest Dermatol, 1992)