The current FAO/WHO definition of probiotics is: “live microorganisms, which, when administered in adequate amounts, confer a health benefit on the host.” Stimulation or improvement of the immune system is a mode of action by which probiotic lactobacilli exerts a beneficial effect to the host.
Adjuvanticity of lactobacilli in enhancing cellular and humoral immune responses has been reported in studies of influenza, polio, and rotavirus vaccines, and rotavirus and Salmonella typhi infections. The immunomodulating mechanism exerted by probiotics is still not fully understood and so is one of the targets of Dr. Yuan’s research.
Studies have indicated that many facets of the immune system are influenced, including increased IgA antibody production; induction of cytokine synthesis; activation of monocytes, macrophages, and dendritic cells; and regulation of the balance of Th1, Th2 and regulatory T cells.
Different probiotic bacteria strains at different doses have different stimulatory and regulatory effects based on different immune status of the host. Further studies are underway in the Yuan lab to clarify the mechanisms of lactobacilli’s immunostimulating effect on rotavirus vaccines in neonatal gnotobiotic pigs.