Elicitation response characteristics to mono- and to N,N'-diacetyl-para-phenylenediamine.

Background: Para-phenylenediamine (PPD) is an important and common cause of allergic contact dermatitis. The mechanism of sensitization is still unknown. It is believed that PPD is a prohapten and thus the balance between activation and/or detoxification processes may influence responses to PPD. Beside auto-oxidation to Bandrowski's base, PPD is enzymatically acetylated to monoacetyl-PPD (MAPPD) and to N,N'-diacetyl-PPD (DAPPD) in skin and keratinocytes.
Objective: We investigated if the 2 acetylated PPD derivatives are able to elicit allergic contact dermatitis by performing epicutaneous skin tests in subjects with dermatitis.
Patients and Methods: Contact allergy to PPD and the 2 acetylated derivatives (1% in petrolatum) were detected by patch testing of 455 patients with eczema from our clinic who were tested with the baseline series.
Results and Conclusions: 16 subjects were found to be patch test positive to PPD (3.5%). No reactions were found for MAPPD, and just 1 PPD-positive patient was positive for DAPPD (0.2%). In agreement with our earlier published in vitro data, these in vivo patch test results indicate that acetylation of PPD can be regarded as a detoxification reaction.