A Comparative Light and Electron Microscopic Study of Primary Irritant Contact Dermatitis and Allergic Contact Dermatitis

Abstract

A detailed sequential study of the early phases of primary irritant and allergic contact dermatitis by means of both light and electron microscopy was undertaken in a search for possible differences not previously appreciated. A primary irritant contact dermatitis was induced in the skin of albino guinea pigs by paintings with 10%, 5% and 1% solutions of 1 chloro 2:4 dinitro benzene (DNCB) in acetone. Allergic contact dermatitis was elicited by application of 0.1% DNCB solution to the skin of animals previously sensitized to this compound. Biopsy specimens were taken from reaction sites at 1, 3, 6, 8, 12, 24 and 48 hours after DNCB application. In primary irritant contact dermatitis, regardless of the irritant concentration used (10%, 5%, 1%), epidermo-dermal separation in the plane between cell membrane and basal, lamina, necrosis of the epidermal cells and dermal polymorphonuclear leukocytic infiltration were regularly observed. Spongiosis and secondary lysosomes were lacking in the separated epidermis but were noted in the epidermis as it regenerated. In allergic contact dermatitis the was no epidermo-dermal separation or cell necrosis but rather the epidermis regularly showed spongiosis and secondary lysosomes. The dermal infiltrate contained numerous basophils which if observed only in H&E stained sections might have been mistaken for eosinophils. Monocytes and lymphocytes appeared simultaneously in the dermis and epidermis and these two cell types frequently were in contact with each other. Macrophages appeared later in the allergic reaction and were filled with secondary lysosomes.