Expression of CD80 (B7/BB-1) and CD28 in human white blood cells treated with urocanic acid.

Urocanic acid (UCA) is formed in the epidermis where it accumulates to be converted from trans- to cis-UCA by ultraviolet (UV) radiation. The two isomers modulate immune functions in several experimental systems. In particular, cis-UCA has been shown to induce antigen-specific immune tolerance, but the molecular mechanism of this effect is unknown. The present investigation was instituted to disclose any effect of UCA isomers on the cellular expression of the costimulatory antigens CD80 (B7/BB-1) and CD28. CD80 expression was efficiently induced in monocytic (CD14+) cells by human interferon-gamma, while CD28 levels on lymphocytes remained unchanged, as detected by flow cytometry. Neither UCA isomer showed any effect on the expression patterns of these costimulatory molecules. The results obtained suggest that the mode of action for epidermal UCA-induced tolerogenesis may not involve modulation of CD80 (B7/BB-1) or CD28 expression.