Predominantly indurated reactions to sensitizers may not cause keratinocytes to express HLA-DR

Dermal reactions to primary intradermal or appendageal sensitization are compared to predominantly dermal reactions to standard patch tests and to intradermal antigen tests. In contrast to epicutaneous spongiotic contact dermatitis, HLA-DR was only seen on skin appendages and nearby basal keratinocytes in indurated tissue reactions with the exception of the reactions with focal basal cell layer disruption and an indurated patch test performed one week post angry back syndrome. Other intradermal skin tests showed only minimal epidermal HLA-DR expression despite spongiotic epidermal changes. Predominantly dermal hypersensitivity reactions can be induced by intradermal or epicutaneous routes. They can evoke hypersensitivity responses which do not cause most epidermal keratinocytes to express HLA-DR.