Effect of retinyl palmitate and 13-cis retinoic acid on immune functions in immunodeficient, nude mice.

Nude mice are deficient in thymus gland development and hence lacking functional, mature T-lymphocytes. Weanling nude mice were given various deficient and high retinyl palmitate (RP) or 13-cis retinoic acid (CRA) diets. The high RP (vitamin A) diets stimulated phagocytosis in the absence of mature T-helper cells. However, T-cell dependent mitogens did not cause significant mitogenesis in any group, while LPS, a B-cell mitogen, did. RP had no effect on mitogenesis. NK cell activity was increased only at a very high level of RP, as has been reported with conventional mice. Macrophage production of cytotoxic factors was unaffected by high levels of RP or CRA. Direct cytotoxicity in vitro of tumor cells was increased only at very high RP levels. Thus, mature T cells may be needed for RP to produce normal activation of macrophage, except at very high RP levels.