The effect of a vitamin A acetate diet on ultraviolet radiation-induced immune suppression as measured by contact hypersensitivity in mice

The adverse health effects caused by increased exposure to ultraviolet radi ation (UVR) due to deterioration of stratospheric ozone are of major concer n, These health effects include sunburn, skin cancer, cataracts and immune suppression, Immune suppression has been associated with the release of cyt okines, a defect in antigen presentation, induction of suppressor T cells a nd suppression of contact hypersensitivity (CH). CH is typically assessed b y the mouse ear swelling test (MEST). Previous studies have demonstrated en hanced CH responses with vitamin A acetate (VAA) dietary supplementation as sessed by MST and the loca lymph node assay (LLNA), To determine the effect that VAA has on UVR-induced immune suppression, Re examined both the induc tion and elicitation phases of CH using murine models, The MEST was used to evaluate the interaction of UVR and VAA on CR elicitation. However, a posi tive MEST response requires that the induction phase as well as the elicita tion phase of CH be functional, The LLNA was used to evaluate the interacti on of UVR and VAA only on CH induction. We tested the hypothesis that mice maintained on a VAA-enriched diet are more resistant to UVR-induced immune suppression (CH) than those maintained on a control diet. Mice were maintai ned on a VAA-enriched or the control diet for 3 weeks and then exposed to U VR 3 days prior to sensitization with 2, 4-dinitrofluorobenzene (DNFB). VAA enhanced the MEST response in both UVR-exposed and non-UVR-exposed mice. T he VAA-enriched diet did not significantly alter the LLNA response in eithe r UVR- or non-UVR-exposed mice, However, there was significant suppression in CH by UVR as measured by the LLNA. These results indicate that (1) the V AA-enriched diet does not restore the number of proliferating cells in the CH induction phase of UVR-induced immunosuppression; (2) the immunosuppress ive effects of UVR affect the induction phase of CH; and (3) the LLNA shoul d be examined as an alternative to the MEST for measurement of UVR-induced immunosuppression, The data indicate that the VAA-enriched diet enhanced th e elicitation response (MEST) but not the earlier induction phase (LLNA). F urther studies are necessary to define mechanisms of action, but modulation of cytokines and effects of specific lymphocyte subsets, as well as system ic effects and local modulation at the site of elicitation are possible, Ad ditionally, future studies to evaluate the effect of the VAA-enriched diet when multiple doses of both UVR and DNFB are used would be of interest for both the LLNA and MEST endpoints.