Probiotics: Role in immunomodulation and consequent effects

Abstract

Microbiologically gastrointestinal tract (GIT) is one of the most active ecosystems with rich diversity of microflora and this gut microbial ecosystem is very crucial for the development and maturation of the of GIT associated immune system. The probiotics mediate their effects by regulating various immune cells, such as T regulatory cells, effector lymphocytes, natural killer T cells, B cells, dendritic cells, and epithelial cells. The gut microbiota is very instrumental in the development and immunomodulation of mucosal immune system and any sort of impairment might result in development of microbiota-related diseases. There are two major mechanisms underlying the immunomodulatory actions of probiotics – regulation of gene expression and signaling pathways in the host cells. The immunomodulatory effect is achieved by: a) direct stimulation of residing immune cells in the GIT, which results in macrophage activation and enhanced phagocytosis, b) modulation of enzyme activity by changing the microbial metabolism. On exposure to any foreign antigen an immune response is initiated by host gut mucosal immune system to maintain the homeostasis partly by adaptive immune response and partly by inducing inflammation. The advancement in the knowledge of intestinal microbiota as a result of metagenomics strategies has provided us a greater understanding of underlying mechanisms of how gut microorganisms affect the body functions. Significant amount of encouraging data pertaining to studies on humans and animal models show that supplementation of probiotics are promising approaches for prevention and treatment of GIT and immune disorders. The effects of probiotics have been observed beyond GIT and the interaction between GIT and central nervous system have revealed the role of neurochemical signalling in gut homeostasis and mental health. However, there is uncertainty in reproducibility of the effects of probiotic supplementation in animal or human nutrition and also there is no information whether the probiotics used in animal nutrition enter the human food chain or not.