DIETARY BETA-CAROTENE AND ULTRAVIOLET-INDUCED IMMUNOSUPPRESSION

Ultraviolet (UV)-induced immunosuppression is a critical step in UV ca rcinogenesis, permitting tumour outgrowth. We investigated the effect of dietary beta-carotene on UV suppression of contact hypersensitivity (CHS) to trinitrochlorobenzene (TNCB) in BALB/c mice. Mice were fed f or 10-16 weeks chow alone or supplemented with 1% beta-carotene or pla cebo as beadlets. Serum beta-carotene was detectable by high performan ce liquid chromatography (HPLC) analysis only in beta-carotene-fed mic e (206 +/- 0.15 mu g/ml). Serum retinol was 0.22-0.27 mu g/ml in all t hree groups. Mice (n=41/dietary group) were irradiated with 0, 4.5, 9 or 18 kJ/m(2) of UVB and the CHS response was measured. Decreased CHS responses were observed in all UV-irradiated groups compared with unir radiated controls. UV dose-responses for suppression of CHS derived by first-order regression analyses of plots of percentage suppression of CHS as a function of log(10)UV dose showed significant slopes (P < 0. 02) for all three dietary groups and similar residual variances betwee n groups, P > 0.05. The UV pose for 50% suppression of CHS was 6.3 kJ/ m(2) for control, 6.4 kJ/m(2) for placebo, and 5.5 kJ/m(2) for beta-ca rotene-fed mice. No significant differences in slopes or elevations be tween UV dose-responses were observed, P > 0.05. Skin levels of the in itiator of UV-induced immunosuppression, cis urocanic acid, were deter mined by HPLC in mice given 0 or 9 kJ/m(2) of UV (n = 28/dietary group ). No significant differences were observed between dietary groups (ra nge 35.2-41.1 ng/mg skin, P > 0.15) We conclude feeding beta-carotene to BALB/c mice does not alter susceptibility to UV immune suppression, in contrast to human studies.