Historical overview

In the years soon after its discovery, vitamin A became suspected of being a factor essential for the development of the lymphoid system and for the maintenance of mucosal surfaces of the gastrointestinal, respiratory and genitourinary tracts (Clausen, 1934; Robertson, 1934) and the high childhood morbidity and mortality in Europe and the USA in the early 20th century - comparable to those found in many developing countries today - were ascribed to the deficiency of vitamin A (Bloch, 1924). Milk, cream and butter were advocated to reduce infections in children (Bloch, 1924). Subsequently, vitamin A was evaluated in at least 30 therapeutic trials in various infections (e.g. Green and Mellanby, 1928; Ellison, 1932). It is now recognized that vitamin A modulates many different aspects of immune function, including components of both nonspecific immunity (e.g. phagocytosis, maintenance of mucosal surfaces) and specific immunity (e.g. generation of antibody responses). Much of our knowledge of vitamin A and immune function is derived from experimental animal studies involving mice, rats and chickens. The effects of vitamin A deficiency on aspects of immune function are summarized in Table 8.1.

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