AUTHOR=Stavropoulou Elisavet , Bezirtzoglou Eugenia TITLE=Probiotics in Medicine: A Long Debate JOURNAL=Frontiers in Immunology VOLUME=Volume 11 - 2020 YEAR=2020 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2020.02192 DOI=10.3389/fimmu.2020.02192 ISSN=1664-3224 ABSTRACT=During the last years probiotics gained the attention of clinicians for their use in the prevention and treatment of multiple diseases. Probiotics main mechanisms of action include enhanced mucosal barrier function, direct antagonism with pathogens, inhibition of bacterial adherence and invasion capacity, boosting of the immune system and regulation of the central nervous system. It is accepted that there is a mutual communication between the central nervous system and the liver, the so-called “microbiota-gut-liver axis” as well as a reciprocal communication between the intestinal microbiota and the central nervous system through the “microbiota-gut-brain axis”. Moreover, recently the gut–lung axis in bacterial and viral infections is considerably discussed as the intestinal microbiota amplifies the alveolar macrophage activity having a protective role in the host defense against pneumonia. The importance of the normal human intestinal microbiota is recognized in the preservation of health. Disease states such as, infections, autoimmune conditions, allergy and other are occurring when the intestinal balance is disturbed. Probiotics seems to be a promising approach to prevent and even reduce the symptoms of these clinical states as an adjuvant therapy by preserving the balance of the normal intestinal microbiota and improving the immune system. The present review states globally all different disorders in which probiotics were given. Stronger data in favor of their clinical use are provided in the prevention of gastrointestinal disorders, antibiotic-associated diarrhea, allergy and respiratory infections. We discuss hereby the role of probiotics in the reduction of the respiratory infections symptoms with a focus on the possibility to be used as an adjuvant to the therapeutic approach of the pandemic COVID-19.Nevertheless, it is accepted by the scientific community that more clinical studies should be undertaken in large samples of diseased populations so that the assessment of their therapeutic potential provide us with strong evidence for their efficacy and safety in clinical use.