ABSTRACT
Contents 22.1 Introduction ................................................................................................................... 440 22.2 Probiotics and Modulation of Immune Function ........................................................... 440
22.2.1 Effect on Mucosal Immunity .............................................................................. 441 22.2.1.1 Intestinal Epithelial Cells ..................................................................... 441 22.2.1.2 Gut Mucosal Barrier Function .............................................................. 441 22.2.1.3 IgA Production ..................................................................................... 441
22.2.2 Effect on Systemic Immunity .............................................................................. 442 22.2.2.1 Phagocytic Activity ............................................................................... 442 22.2.2.2 NK Cell Activity .................................................................................. 467 22.2.2.3 Acquired Immunity .............................................................................. 467 22.2.2.4 Effect on Cytokine Production ............................................................. 480
22.3 Probiotics-Induced Immunoenhancement and Disease Resistance ..................................481 22.3.1 Gastrointestinal Infections ...................................................................................481 22.3.2 Extraintestinal Infections .................................................................................... 482 22.3.3 Respiratory Tract Infections ................................................................................ 482 22.3.4 Urogenital Infections .......................................................................................... 494 22.3.5 Cancer ................................................................................................................ 494
22.4 Probiotics and Immunoinflammatory Disorders .............................................................495 22.4.1 Allergies ...............................................................................................................495 22.4.2 Inflammatory Bowel Disease .............................................................................. 496 22.4.3 Irritable Bowel Syndrome ................................................................................... 497
22.5 Mechanisms by Which Probiotics Mediate Their Immunomodulatory Effects ...............498 22.6 Conclusion ......................................................................................................................498 References ............................................................................................................................... 499
22.1 Introduction The human gastrointestinal tract (GIT) represents the largest body surface area exposed to the external environment. It is continuously challenged by a diverse array of environmental, dietary, and microbial antigens (derived from the enteric flora). In addition to facilitating digestion and allowing absorption of nutrients, the GIT performs a very complex and delicate function of exhibiting tolerance to innocuous environmental antigens and enteric flora, but at the same time mounting an aggressive immune response toward pathogenic organisms. Failure to tightly regulate these responses leads to enhanced susceptibility to infectious diseases and immunoinflammatory disorders. To perform these functions efficiently, the GIT is endowed with the largest immune system in the body.
