Urocanic acid suppresses induction of immunity in human skin
Trans-urocanic acid is isomerized to cis-urocanic acid (C-UCA) by ultraviolet radiation. C-UCA suppresses immunity in vitro and in vivo in animals; its effect on human skin is unknown. We sought to determine whether its topical application to normal skin suppresses induction of immunity to dinitrochlorobenzene (DNCB). Methods:
Forty subjects applied C-UCA (0%, 0.02%, 0.2%, or 2%) for 17 days. A 40-mcg dose of DNCB was then applied to induce immunity. Subjects were challenged for immunity at 6-week follow-up by occluding doses of DNCB (0, 3.125, 6.25, or 12.5 mcg) on untreated normal skin. Induced immunity was measured by area of erythema and induration 2 and 4 days postchallenge. Results:
No significant differences were found in incidence of sensitization by C-UCA concentration (P=.59). DNCB sensitization developed in all 10 subjects induced through 0% C-UCA (placebo); only 23 of 30 patients were sensitized through skin treated with C-UCA. Mean areas of erythema and induration induced through C-UCA-treated skin were less than those in controls (P<0.05). The number of Langerhans cells in C-UCA-treated skin was unaffected. Laboratory tests of immune function and lymphocyte numbers were unchanged. Conclusion:
Topically applied C-UCA blunts normal induction responses to a cutaneous sensitizer.
Document Type: Research Article
Affiliations: 1: Department of Dermatology, Mayo Clinic, Scottsdale, AZ, USA 2: The Cosmetic, Toiletry, and Fragrance Association, Washington, DC 3: Department of Dermatology, The University of Minnesota Medical School, Minneapolis, MN, USA
Publication date: 2010-12-01