Characterization of a monoclonal antibody to cis-urocanic acid: detection of cis-urocanic acid in the serum of irradiated mice by immunoassay.

Cis-urocanic acid (cis-UCA), which is formed from the naturally occurring trans-isomer on ultraviolet (UV) irradiation, has been suggested as a photoreceptor for and mediator of the suppressive effects of UV irradiation on systemic immune responses. Trans-UCA is located predominantly in the stratum corneum, and the extent of isomerization to cis-UCA may be analysed by high-performance liquid chromatography (HPLC) of skin extracts. Such an analysis is not suitable for other tissues. In this study a murine monoclonal antibody to cis-UCA was prepared and tested by ELISA using UCA isomers conjugated to protein as antigens. The interaction of the antibody with structural analogues of UCA was assessed by competitive inhibition ELISA which indicated that the antibody had a high specificity for cis-UCA. Screening of sera at various times after UVB irradiation of mice by competitive inhibition ELISA using the monoclonal antibody showed that cis-UCA was present, probably in an unbound form, for at least 2 days after the exposure. Thus, cis-UCA produced in the epidermis following UVB irradiation reaches the serum a few hours later. The implications of this finding for the generation of suppressed immune responses are discussed.