Urocanic acid isomers, immunosuppressive cytokines and the induction of human immunodeficiency virus.

The ability of cis-urocanic acid to mimic the effects of ultraviolet (UV) was tested in two systems that show cellular responses to direct UV irradiation. First, cultured mouse keratinocytes were treated with cis-urocanic acid and the cell culture supernatants were injected into mice to test for the ability to block spleen cell proliferation in the mixed lymphocyte reaction. Second, human fibroblasts carrying the chloramphenicol acetyltransferase gene under the control of the human immunodeficiency virus (HIV) long terminal repeat promoter were tested for the ability of cis-urocanic acid to induce gene expression. In these tests cis-urocanic acid did not induce a response comparable with UV irradiation alone, although at toxic concentrations cis-UCA did induce low expression from the viral promoter. These data suggest that, unlike UVB radiation, cis-urocanic acid does not activate keratinocytes to produce immunosuppressive cytokines nor does it induce expression of the HIV promoter.