Vitamin A deficiency decreases natural killer cell activity and interferon production in rats.
 We examined the effect of vitamin A deficiency on natural killer (NK) cell activity and interferon (IFN) production.
 Rats were weaned at 16 or 21 d of age onto semisynthetic diets containing either 0 or 4 micrograms retinol/g diet.
 At the time of study, retinol-depleted rats had serum vitamin A concentrations less than 7% of those of pair-fed controls.
 In two studies, rats exhibited no external signs of retinol deficiency, but with further depletion some symptoms were observed.
 Splenic NK cell activity against chromium-51-labeled YAC-1 cells was significantly decreased in vitamin A-depleted rats (22-80% of values for control rats, depending on the degree of retinol deficiency), regardless of the ratio of effector to target cells used.
 When vitamin A-depleted rats were repleted orally with retinol, NK cell activity was consistently normalized.
 To understand the possible mechanisms involved in decreasing NK cell activity, we investigated IFN production by concanavalin A-stimulated spleen cells from vitamin A-depleted, from repleted and from control animals.
 IFN titers were significantly decreased (22-33% of values for control rats) in supernatants of spleen cell cultures of the vitamin A-depleted rats.
 Repletion with vitamin A resulted in IFN activities ranging from 80 to 130% of controls.
 Adding alpha/beta IFN in vitro to the spleen cells of vitamin A-depleted animals increased their NK cell activity.
 The number of spleen cells reacting with a monoclonal antibody specific for rat NK cells was slightly lower in retinol-depleted rats, but not enough to account for the differences in NK cell and IFN activities.
 These data suggest that vitamin A deficiency affect the nonspecific arm of the immune system, possibly by altering the functional capacity of cells to produce lymphokines needed for the generation of an appropriate cytolytic response.
