Constitutive endothelial and inducible nitric oxide synthase in inflammatory dermatoses.

We have used immunohistochemistry to localize the expression of the constitutive endothelial and inducible forms of the enzyme nitric oxide synthase (NOS) in skin from involved and uninvolved sites in patients with atopic dermatitis (AD) and allergic contact dermatitis (CD). Endothelial NOS (eNOS) immunoreactivity was localized to vascular endothelium in the dermis of both involved and uninvolved skin from all patients. Inducible NOS (iNOS) immunoreactivity was found to be closely associated with the upper dermal microvasculature in all the involved AD biopsies, but only in two of 10 uninvolved AD biopsies. CD biopsies were taken from 10 positive skin patch test sites and iNOS immunoreactivity was detected in all of these. iNOS immunoreactivity was detected in only one of the negative patch test biopsies. Both the extent and intensity of iNOS immunoreactivity was lower in CD than in AD skin lesions. The presence of eNOS in the skin is necessary for constitutive NO-mediated dilatation of the dermal vasculature. Induction of iNOS in the dermal endothelium and in perivascular inflammatory cells may be significant with respect to the roles of NO in both the vasodilatory component of the inflammatory response and in the modulation of immune responses in the skin.