Abstract: Tos tudy the possible immunosuppression mechanism of cis-urocanic acid(cis-UCA)ir-radiated by UV,the proliferation test by phytohemagglutinin(PHA) was carried out to investigate whether and how the cis-UCA、trans-UCA and histamine phosphate influence the Tlymphocyte.Also it was disscused if the H₂ receptor of Tlymphocyte play an important role in the immunosuppression of cis-UCA and histamine.Th eresults showed that 0.2 mmol/L cis-UCA and 0.2 mmol/L histaminephos-phate significantly inhibited the Tlymphocyte proliferation by PHA,however,0.2 mmol/L trans-UCA did not.2.0 mmol/L cimetidine could block the inhibitory effects of cis-UCA and histamine phosphate.The seresults indicate that cis-UCA can inhibit the Tlymphocyte proliferation by H₂ receptor,further-more,immunosuppression mechanism of cis-UCA may be similar to histamine.

Key words: Urocanic acid, Receptors, histamine H₂, Immunosuppression