Effects of β-carotene and retinol repletion on antibody production in vitamin A-deficient rats immunized with pneumococcal polysaccharide

Experiments were conducted in male Lewis rats to compare the efficacy with which β-carotene (βC) and retinol restore antibody production in the previously vitamin A-depleted rat immunized with pneumococcal polysaccharide (SSS-III). Weanling rats were fed a semipurified vitamin A-free diet for three weeks and were then repleted with either retinol or βC provided in various doses and by different routes. Pairfed control rats were fed the same diet with adequate vitamin A. When 45-46 days old, rats were immunized with SSS-III and antibody production was measured 5 d later. In rats beginning to manifest vitamin A deficiency, the splenic antibody response was reduced significantly in comparison to that of the pairfed control group as well as to groups repleted with retinyl palmitate or with βC [1500 retinol equivalents (R.E.) each]. When βC was provided in an aqueous dispersion and delivered either orally or intravenously, the splenic antibody response of both βC-repleted groups were similar to each other and both were significantly greater than the response of the vitamin A-deficient group. The antibody response of rats repleted intravenously with βC or retinol, provided in nutritionally equivalent amounts (1000 R.E.), was also similar in magnitude. These observations indicate that βC functions approximately equally well as retinol in enabling the previously vitamin A-deficient rat to respond to pneumococcal polysaccharide; however, βC did not show any superior effect to retinol in restoring this antibody response in the previously vitamin A-depleted rat.