ZINC AND IMMUNE FUNCTION - THE BIOLOGICAL BASIS OF ALTERED RESISTANCETO INFECTION

Zinc is known to play a central role in the immune system, and zinc-de ficient persons experience increased susceptibility to a variety of pa thogens. The immunologic mechanisms whereby zinc modulates increased s usceptibility to infection have been studied for several decades. It i s clear that zinc affects multiple aspects of the immune system, from the barrier of the skin to gene regulation within lymphocytes. Zinc is crucial for normal development and function of cells mediating nonspe cific immunity such as neutrophils and natural killer cells. Zinc defi ciency also affects development of acquired immunity by preventing bot h the outgrowth and certain functions of T lymphocytes such as activat ion, T(h)1 cytokine production, and B lymphocyte help. Likewise, B lym phocyte develop ment and antibody production, particularly immunoglobu lin G, is compromised. The macrophage, a pivotal cell in many immunolo gic functions, is adversely affected by zinc deficiency, which can dys regulate intracellular killing, cytokine production, and phagocytosis. The effects of zinc on these key immunologic mediators is rooted in t he myriad roles for zinc in basic cellular functions such as DNA repli cation, RNA transcription, cell division, and cell activation. Apoptos is is potentiated by zinc deficiency. Zinc also functions as an antiox idant and can stabilize membranes. This review explores these aspects of zinc biology of the immune system and attempts to provide a biologi cal basis for the altered host resistance to infections observed durin g zinc deficiency and supplementation.