[Influence of natural gut flora on immune response]

Our intestines are habitat for trillions of microorganisms such as bacteria, viruses and eukaryotes, known as microbiota. They are indispensable for our well-being due to their metabolic activities. Microbiota digests complex plant polysaccharides, which are normally unprocessed by humans; as well it retrieves other essential nutrients. It is well established that microbiota is crucial for proper development of intestinal as well systemic immune compartments. Recent results indicate that composition of natural gut flora is responsible for shaping of immune response. Alerted bacterial profile, known as dysbiosis precedes development of allergy in children. Many autoimmune conditions are associated with shift in intestinal bacterial profile. Apart of direct association between gut flora and systemic immune compartment little is known about the mechanisms by which microbiota exerts its immunoregulatory function. At the moment several bacterial strains as well some bacterial products were recognized as immunomodulators. This review describes the composition of normal gut flora as well disease-associated microbiota. It deals with unique mechanisms, found in GALT, that favor induction of tolerance towards orally administrated antigens as well discriminate between commensal and pathogens to minimize induction of inflammatory response. Further, the review tries to establish the connection between microbiota and systemic immune response. Finally the factors that modulate the composition of our gut flora are described.