Histological aspects of DNCB sensitization and challenge tests.

I. A group of twenty-one Caucasian volunteers was patch tested without preliminary sensitization with 3, 10, 30, 50 and 90 mug 2,4-dinitrochlorobenzene (DNCB)/cm2. Of this group seven persons were read after 24 h; with one exception all showed a toxic erythematous reaction to 30 mug and higher amounts of DNCB/cm2. The other fourteen volunteers were read after 48 h. All except one reacted positively to 30 mug and higher amounts of DNCB/cm2. Histologically no changes could be noted after application of 3 and 10 mug DNCB/cm2; they started to appear in patch tests with 30 mug DNCB/cm2 or more. II. A second group of twenty-one Caucasian volunteers was sensitized with 2000 mug DNCB on a surface area of 3-14 cm2. Biopsies were performed after 1 h, 5 h, 1 day and then daily for 17 days. The histological changes occurring in the sensitization site during the primary irritant reaction of the first days were compared with the changes occurring during the flare-up reaction. No essential qualitative differences could be noted. III. Four Caucasian volunteers were sensitized with 2000 mug DNCB on 3-14 cm2. Fourteen days later challenge patch test doses of 3, 10, 30, 50 and 90 mug DNCB/cm2 were applied. Biopsies of the challenge sites were performed after 48 h. In contrast to the results in group I, histological changes could already be noted after challenge patch tests with 3 mug DNCB/cm2. The nature ofthe histological changes in primary irritant and allergic reactions to DNCB appeared to be identical and consisted of spongiosis, epidermal degeneration and lymphocytic infiltration around vessles and epidermal appendages and penetrating into the epidermal layers. It is concluded that, in order to avoid errors through misinterpretation, challenge patch tests with DNCB must be performed with low amounts, e.g. 3 or 10 mug/cm2.