Abstract
Although studies conducted over the last twenty-five years have demonstrated that vitamin A and related retinoids are immune enhancers, the use of vitamin A and related retinoids to enhance responses to immunization has been limited. Numerous animal studies have now demonstrated that vitamin A and related retinoids, when given at or prior to immunization, will enhance antibody responses and cell-mediated immune responses to protein antigens. Recent studies with humans show that vitamin A supplementation enhances the IgG response to tetanus toxoid, and that related retinoids can be used to enhance antibody responses to protein antigens.
Vitamin A enhances immune responses to poor immunogens, and this may be relevant to vaccines which are characterized by low se-roconversion rates. Although most known adjuvants have too many side effects for human use, vitamin A and related retinoids appear to enhance antibody and cell-mediated immunity without severe side effects. Vitamin A, through its metabolites, acts to modify biological responses through specific nuclear receptors which activate gene transcription. Thus, the mechanism for immune enhancement by vitamin A appears to be different from that of known adjuvants. Vitamin A and related retinoids have potential as a safe and effective means of enhancing immune responses to vaccination antigens.