Abstract
The importance of vitamin A on immune system functions can be demonstrated, in part, by in vitro studies of blood or tissue lymphocytes obtained from animals or human beings. Mitogenic responsiveness of splenic T-cells was depressed in vitamin A-defi-cient rats, as compared to pair-fed controls, at different stages of vitamin A restriction. However, the impairment in mitogenic responsiveness of T-cells from peripheral blood did not become apparent until vitamin A deprivation was well established. Smaller degrees of impairment were also seen in the pair-fed control rats, demonstrating the concomitant importance of energy intake.
Other important variables were identified by studying the in vitro mitogenic responsiveness of lymphocytes to antigens to which the rats had been previously exposed. Important variables (which could influence the results of dietary deprivation studies) included the sources of the lymphocytes, differences in routes of immunization, and the systemic activation caused by adjuvants.
Reports are limited concerning the effects of different degrees of vitamin A deficiency on the mitogenic responsiveness of blood lymphocytes from children who are free of protein-energy malnutrition. No difference was found (using whole blood culture techniques) in the in vitro proliferative responsiveness of T-cells to Con-A and tetanus toxoid of children with normal or low-normal concentrations of vitamin A or zinc. The whole blood culture techniques can be used to measure lymphocyte production of IL-2 and IL-4 (which is not impaired in A-deficient mice).