Dietary β-carotene and ultraviolet-induced immunosuppression

Abstract

Ultraviolet (UV)-induced immunosuppression is a critical step in W carcinogenesis, permitting tumour outgrowth. We investigated the effect of dietary,B-carotene on UV suppression of contact hypersensitivity (CHS) to trinitrochlorobenzene (TNCB) in BALB/c mice. Mice were fed for 10-16 weeks chow alone or supplemented with 1% β-carotene or placebo as beadlets. Serum β-carotene was detectable by high performance liquid chromatography (HPLC) analysis only in β-carotene-fed mice (2.06 ± 0.15 μg/ml). Serum retinol was 0.22-0.27 μg/ml in all three groups. Mice (n=41/dietary group) were irradiated with 0, 4.5, 9 or 18 kJ/m2 of UVB and the CHS response was measured. Decreased CHS responses were observed in all UV-irradiated groups compared with unirradiated 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 log10UV dose showed significant slopes (P < 0.02) for all three dietary groups and similar residual variances between groups, P > 0.05. The UV dose for 50% suppression of CHS was 6.3 kJ/m2 for control, 6.4kJ/m2 for placebo, and 5.5 kJ/m2 for β-carotene-fed mice. No significant differences in slopes or elevations between UV dose-responses were observed, P > 0.05. Skin levels of the initiator of UV-induced immunosuppression, cis urocanic acid, were determined by HPLC in mice given 0 or 9 kJ/m2 of W (n=28/dietary group). No significant differences were observed between dietary groups (range 35.2-41.1 ng/mg skin, P > 0.15) We conclude feeding β-carotene to BALB/c mice does not alter susceptibility to UV immune suppression, in contrast to human studies.