Immunotrophic methodology

Interest in the immunoregulatory properties of vitamin A stems from three types of observations: the susceptibility of vitamin A-deficient humans and animals to infection; the association of vitamin A deficiency with depressed immune responses; and the stimulating effects of excess vitamin A, retinoic acid, and synthetic retinoids on various immune parameters. A large number of in vitro and in vivo immunologic assays have been used to assess immunocompetence in these studies. This chapter discusses the tests used most frequently to evaluate immunologic status in vitamin A-deficient or retinoid-supplemented human and animal subjects. The chapter provides an overview of the methodologies available to identify retinoid-associated immunosuppression or immune enhancement. It discusses interpretation of the data and indicates the strengths and limitations of the different assays when applied to nutritional or pharmacological studies.