Studies of the quenching phenomenon in delayed contact hypersensitivity reactions

Abstract

Studies in guinea pig and man have shown that eugenol can quench non-specifically contact urticarial responses, whereas limonene seems largely ineffective. In a comprehensive series of studies, there was little evidence of quenching of delayed contact hypersensitivity reactions to cinnamic aldehyde or citral, including in 'pre-quenched' material supplied by a perfume/flavour company, and in a similar mixture prepared in this laboratory, in the guinea pig model. In addition, there was no evidence of the quenching by eugenol of allergic reactions to cinnamic aldehyde in a panel of human subjects with a proven history of cinnamic-aldehyde-induced allergic contact dermatitis. Overall, the results lend little credibility to earlier literature reports of quenching phenomena in delayed contact hypersensitivity responses.

Quenching: fact or fiction?

“…Let us consider the outcome of the published guinea pig work (12,13) in more detail. Studies were conducted in OECD standard assays (14), which encompass both adjuvant and non-adjuvant tests, as well as in non-standard methods.…”

“…In the work of the Strasbourg group, using a guinea pig predictive test, the effect of limonene on the induction of skin sensitization to citral, unfortunately, was not examined (8). This variable was investigated thoroughly, however, in an extensive series of investigations using a variety of guinea pig models (12,13). The outcome of these studies can be summarized quite simply -no quenching effect could be demonstrated.…”

“…The efficacy of quenching agents during elicitation has been examined in man using a small panel of subjects with proven clinical allergy to cinnamal (12). Patch testing was carried out for 48 h with a range of doses of cinnamal in the presence and absence of eugenol.…”

“…So, can quenching be shown to operate at this level? As with induction, a substantial body of work has been carried out in the guinea pig model (12,13). Studies were conducted with cinnamal/eugenol and citral/limonene.…”

“…Eugenol quenches cinnamal; limonene either has no effect (guinea pig model) (12,13) or may enhance the sensitizing activity of cinnamal (man) (18). This suggests either a specific chemical interaction, or a specific immunobiological event, such as haptenic competition.…”