A comparative study of allergic and primary irritant contact dermatitis with dinitrochlorobenzene (DNCB) in dogs.

Attempts were made to induce allergic contact dermatitis in dogs, a species generally considered poorly responsive to experimental allergic contact dermatitis. Yound Beagles were sensitized to 2,4 dinitrochlorobenzene (DNCB) by multiple intradermal injections. Two weeks after sensitization, these dogs were challenged topically with 0.1% DNCB by a standard closed-patch technique. Sensitization evidenced by various degrees of reaction following challenge was established in all of 14 pups used, while 7 nonsensitized control pups did not react to challenge. Primary irritant contact dermatitis was induced in the skin of nonsensitized Beagle pups by 1%, 5%, and 10% solutions of DNCB. In allergic contact dermatitis the sites of challenge were grossly indurated, erythematous, and edematous. Histologically at these sites there was an infiltration of mononuclear cells which reached maximum intensity at 3 to 4 days. Accumulations of lymphoid cells were marked around sweat galnds and hair follicles. Penetration of leukocytes into these cutaneous adnexa was associated with degenerative processes in their cellular structures. Mononuclear cell infiltration into the epidermis was mild. Spongiosis was observed in the epidermis, but vesicle formation was rare. In primary irritant contact dermatitis gross lesions were characterized by severe erythema, edema, and gangreen of the skin. Microscopically, the main lesions were necrosis of the epidermal cells, separation of the epidermis from the dermis, dermal edema, and massive infiltration of the dermis with polymorphonuclear cells.