Analysis of the Cytokine Pattern Expressed In Situ in Inhalant Allergen Patch Test Reactions of Atopic Dermatitis Patients

In the present study, we examined the cytokine pattern expressed in situ during the development of eczematous reactions that had been provoked in atopic dermatitis patients by patch testing with house dust mite allergen. In 24-h house dust mite allergen patch test reactions, expression of interleukin (IL)-4 mRNA and IL-2 mRNA increased, but interferon (IFN)-γ mRNA did not, as compared with control skin. In 48-h inhalant allergen patch test reactions, however, IFN-γ mRNA and IL-2 mRNA expression were increased above levels observed in control skin, whereas IL-4 mRNA expression was decreased below background levels. These data demonstrate that a switch from a Th2-like to a Th1-like cytokine response occurs in inhalant allergen patch tests of atopic dermatitis patients. This biphasic pattern was specific to inhalant allergen patch test reactions, as it was not observed in irritant reactions in the same patient. IFN-γ production by T cells may be induced by the cytokine IL-12. In the present study, up- regulation of IFN-γ mRNA expression in inhalant allergen patch test reactions was preceded by an increased expression of the p35 subunit of IL-12 mRNA. These observations suggest that increased IL-12 expression may contribute to the observed switch of the in situ cytokine secretion pattern. Further studies are necessary to determine whether a similar biphasic pattern of cytokine expression is also operative in the initiation phase of atopic eczema.