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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: OBJECTIVE, METHODS, RESULTS. Meshes: Adult, Dinitrochlorobenzene, Erythema, Female, Humans, Immunosuppressive Agents, Langerhans Cells, Male, Middle Aged, Skin, Stereoisomerism, Time Factors, Ultraviolet Rays, Urocanic Acid.
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Does urocanic acid suppress induction of immunity in human skin? Context: 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). 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. 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.
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Topically applied C-UCA blunts normal induction responses to a cutaneous sensitizer. Final Decision: yes