Reduction of immunosuppression in UV-irradiated mice by dietary retinyl palmitate plus canthaxanthin.

The ability of dietary retinyl palmitate, canthaxanthin or the combination of both, to prevent induction of immunosuppression by UVB irradiation was tested by passive transfer of splenocytes. The basal diet was the American Institute of Nutrition diet 76A, containing 4 IU retinyl palmitate/g diet. Groups of 55 mice were fed this basal diet alone, or supplemented with 120 IU retinyl palmitate/g diet, 1% canthaxanthin or the combination of both. After 18 weeks of these diets, UVB radiation treatments began. The UVB radiation source was a bank of six unfiltered Westinghouse FS40 lamps which delivered an average dose of 4.6 J/m2/s over the wavelength range of 280-340 nm. After 27.5 weeks of UV treatments, and approximately 1.14 X 10(6) J/m2, spleens were removed from mice and used as sources of splenocytes for passive transfer into naive recipients. These recipients were then challenged with an immunogenic, syngeneic UV-induced tumor (UV20). Approximately twice as many tumor challenges grew in recipients of splenocytes from UV-irradiated (19/20), as compared with unirradiated (11/20) donors fed the basal diet. Transfer of splenocytes from UV-irradiated donors fed the basal diet admixed with 1% canthaxanthin, 120 IU retinyl palmitate/g diet or the combination, resulted in 16/20, 13/20 and 10/20 growing tumors, respectively. These values were insignificantly (P = 0.25), marginally (P = 0.054) or significantly (P less than 0.02) different from the positive control value, respectively. Thus, dietary supplementation with retinyl palmitate plus canthaxanthin prevented the transfer of UV-induced immunosuppression with splenocytes from UV-irradiated mice.