UROCANIC ACID IN SYSTEMIC IMMUNE SUPPRESSION

Objective To investigate how ultraviolet B (UVB)-irradiated urocanic a cid (cis-UCA) affects the immune function and possible mechanisms. Met hods Skin grafts were harvested from the tails of C57B mice and placed onto full thickness beds on the flanks of BALB \ C mice (across a com plete MHC Class I and II mismatch). 0.2 ml of 24% cis-urocanic acid, 1 00% transurocanic acid, and saline was separately injected ip into rec ipient mice prior to skin grafting. The skin allograft survival time w as observed and compared between groups. A mice model for delayed-type hypersensitivity (DTH) response to DNP6-OVA which was indicated by in creasing in ear thickness was established. Each mouse in Group A and B was injected respectively with 200 mu g cis-UCA and trans-UCA ip 5 ho urs previous to sensitization with 10 mu g emulsified DNP6-OVA in the subcutaneous of hind legs. Group C was control group,ln which DNP6-OVA remained at the same time. After 7 days, each ear thickness of all mi ce including Group D was measured by micrometer. Mice in the Group D w ere examined by increase of ear thickness caused by the physical stimu lus and other factors. 2 mu g DNP6-OVA were injected into each pinnae thereafter. And each ear thickness was remeasured 24 hours later. The serum IgG, C-3, C-4 level in the mice stimulated by E. Coli was detect ed by ELISA assay. The lymphocytes were cultured with 24% Cis-UCA, tra ns-UCA, histamine, Cis-UCA cimetidine together and histamine cimetidin e together respectively, After 40 hours PHA stimulating, 200 mu l lymp hocytes culture media supernatant were collected from each group to ev aluate the. IL-2 active level with IL-2 depending cells ''CTLL'' by MT T method. 68 hours later following PHA stimulating, lymphocytes prolif eration index (SI) was detected by MTT method. Meanwhile, the total ce lls RNA of each group were extracted by one step extraction method and quantified, then the IL-2 mRNA was detected by RT-PCR. Results Cis-UC A could significantly prolong the allograft skin survival (11.4 +/- 0. 71 / 9.3 +/- 0.22 days, P < 0.05) comparing with the trans-UCA and PBS . Significant immunosuppression of DTH to DNP6-OVA was found in the Ci s-UCA group, the P value < 0.01 (t = 9.48). No same effect was found i n trans-UCA and PBS group. The 24% Cis-UCA immune suppression rate was 47.9%. Also we found that Cis-UCA could significantly inhibit the IL- 2 bioactivity than trans-UCA (3.13 +/- 1.52 / 10.14 +/- 6.21, P < 0.05 ) in the mice stimulated by E. Coli. The humoral immune response could be suppressed by Cis-UCA. The serum IgG level was decreased significa ntly in the Cis-UCA group (t = 4.03, P < 0.01). The serum complement l evel (C-3 and C-4) was also decreased after injecting Cis-UCA (C-3: t = 2.50, P < 0.05; C-4: t = 4.63, P < 0.01). Meanwhile, the results ind icated that normal T lymphocytes proliferation could be inhibited by C is-UCA. The stimulated index (SI) of T lymphocytes could be decreased by Cis-UCA. Same effects were found in histamine group. The inhibited effects could be blocked by cimetidine (H2R blocker). The trans-UCA di d not show the stimulated index inhibiting effect on T lymphocytes. Th e same effects of Cis-WCA upon T lymphocyte's total RNA were found. Th e Cis-UCA and histamine decreasing the cell total RNA could be also bl ocked by cimetidine. Conclusions The ultraviolet immunosuppression may be mainly mediated by Cis-UCA which could effect on the H-2 receptors on T lymphocytes.