Contact Sensitivity to Urushiol: Role of Covalent Bond Formation

A single cutaneous application of components of poison oak or ivy urushiol oils to mice results contact sensitivity with properties of delayed-type hypersensitivity.The compounds,3-heptadecycatechol (HDC,from poison oak urushiol) and 3-pentadecylcatechol (PDC,from poison ivy urushiol) are completely cross-reactive.Covalent bond formatiion between the o-quinone intermediate of PDC and uncleophilic functionalities such as those found on proteins is known to occur in a regiospecific manner.Amino uncleophiles perferenitally attack the 5-position on the catechol ring white thiol nucleophiles attack the 6=position.The present paper descreibes the immunological properties of the three possibls ring monomethylated analogs of PDC.When mice were treated with a single epicutaneous painting with these analogs, only the 5-methyl compound (5-Me-PDC) was found to be an ineffecitive sensitizer.The 5-Me-PDC analog, however, was capable of inducing cellular proliferation in draning lymph nodes.Furthermore, epicutaneous pretreatment with 5-Me-PDC suppressed the subsequent induction of contact sensivity to PDC and HDC in antigen-specific manner.Equivalent treatment with the 6-Me-PDC analog (a good sensitizing agent) resulted in a less consisitent and weaker suppressive effect, while the 4-Me-PDC analog did not display any suppressive activity.The suppressive acitivity coud be demonstrated up to 15 days following primary painting with 5-Me-PDC. Lymph node cells obtaind from mice 10 days after a single painting with 5-Me-PDC could transfer the suppressive effect.Under certain circmstances 5-Me-PDC could also sensitize, indicating that the analge retaims some sensitizing abilities.Hence, blocking the 5-posistion of catechol ring results in a major alteration in the type of immune response elicited.Since 5-Me-PDC is specifically blocked in terms of uncleophilic attack by amino groups,it is suggested that attackd by amino uncleophiles is of primary importance in the peripheral metabolic processing of these catechols, which in turn determines the outcome of the immune response.