Chronic vitamin A status and age as determinants of plasma retinol, its transport proteins, and immune functions

Few studies of aging have been conducted in animals whose nutritional status has been controlled throughout their lifetime. Previously, vitamin A (VA) has been implicated in immune functions in acute studies of VA deficiency and retinoid repletion. We have evaluated how chronic VA nutritional status affects plasma retinol, its transport proteins, lymphocyte populations, and proliferative responses. In a 3 × 3 factorial design, male Lewis rats were fed one of three VA-controlled diets (VA-marginal, control, or VA-supplemented) until the ages of 2-3 mo (young), 10-12 mo (middle-age), or 18-20 mo (old). By 2-factor ANOVA, both diet and age were significant determinants of plasma retinol, retinol-binding protein (RBP), and transthyretin (TTR) concentrations. The molar ratio of retinol:RBP was < 1 for all VA-marginal and control groups, and > 1 for all VA-supplemented groups with an age related increase in the latter. There were age-related declines in the proliferative response to anti-CD3 and anti-CD3/CD28 (T cells), LPS (B cells), and calcium ionophore (nonspecific) (all P<0.0001). There were also significant diet-related effects on responses to anti-CD3 and anti-CD3/CD28; the latter changes can partially be explained by the effect of age and diet on the percentage of OX19+/CD5 T cells in peripheral blood. Thus, within a range of VA intakes that apparently excludes deficiency and toxicity, VA status has significant effects on T cell number and function.