Delayed type hypersensitivity in atopic dermatitis.

Three different aspects of delayed type hypersensitivity in atopic dermatitis (A.D.) were studied. (a) Intradermal testing demonstrated that positive reactions to bacterial vaccines were distinctly lower in patients with A.D. (b) Patch testing in patients with A.D. compared to tests in patients with anal eczema showed a striking difference in results concerning the substances to which positive reactions were found. (c) Patients with A.D. (n = 18), atopics without A.D. (n = 10), patients with contact dermatitis (n = 10), and normal controls (n = 10), were patch tested with various human dander (H.D.) fractions after stripping the stratum corneum with skin tape. Only patients with A.D. showed positive reactions, the maximum response being at 24-48 hours. There was no difference in reaction pattern between partially purified H.D. subfractions. Histopathological examination revealed an eczema-reaction. Patch testing within the same patient groups with purified house dust mite allergen P1 demonstrated similar results. Although this finding argues against a specific role of H.D. allergen in A.D. it may at least be concluded that H.D. preparations have the capacity to provoke immediate as well as delayed type skin reactions.