The way that food-derived substances modulate immune
functions is either indirect or direct. Comparative analyses of
conventional and germ-free animals revealed that indigenous
intestinal microflora play a pivotal role in the development of
host immune systems. Ingestion of probiotics stabilizes the
intestinal microflora, and normalization of the intestinal
microflora by probiotics could lead to modulation of the host
immune system (144). In addition, probiotics such as lactic
acid bacteria are recognized by specific receptors on the
surface of phagocytic cells. Additionally, vitamins, minerals or
fatty acids affect cellular functions by preserving the cell
membrane or regulating gene expression after being incorporated
into lymphocytes (Fig. 3). One group of foods
represented by lactic acid bacteria stimulates innate immunity
(phagocytic activity, NK cell activity), while other foods,
including vitamins and minerals, activate acquired immunity
(T cell response, antibody production). However, as innate
immunity and acquired immunity are closely linked, both
groups of foods may regulate both immune systems. It has
been reported that various nutrients found in foods exhibit
anti-infectious functions (145). We would like to briefly
describe the pathways by which food-derived substances exert
their immune-modulating abilities.