The fate of 2,4-dinitrochlorobenzene, a potent contact sensitizing chemical, and 2,4-dichloronitrobenzene, a non-sensitizer, was compared following their application to the skin of BALB/c mice. Although both chemicals were able to bind to protein in vitro and were capable of being absorbed across mouse skin in vivo, only 2,4-dinitrochlorobenzene was able to bind to cells in the skin and to induce the movement of these cells from the epidermis into the dermis and ultimately into the draining lymph nodes. The sensitization potential of a chemical may therefore be dependent on its ability to associate with and stimulate the efflux of cutaneous antigen-presenting cells.

Epicutaneous application of 2,4-dinitrothiocyanobenzene (DNTB) is said to result in specific immunological hyporesponsiveness and fails to induce contact sensitization. However, we demonstrate that topical exposure to DNTB causes activation of the draining lymph node in mice and the induction of contact sensitization in both rodents and a single human volunteer. In mice and rats, pre-exposure to DNTB failed to impair subsequent responsiveness to the cross-reactive allergen 2,4-dinitrochlorobenzene. These data provide evidence that DNTB cannot be regarded as an exclusive tolerogen when applied epicutaneously and indicate that attempts to define the characteristics of tolerising chemicals from analysis of this agent may be misleading.