Système immunitaire muqueux et microbiote intestinal : Histoire d'une symbiose

Human foetus develops in a sterile environment. Mucosal and cutaneous colonisation begins at birth, with acquisition of his mother's vaginal, fecal and cutaneous flora. Age, nutrition, environment introduce quantitative and phylogenic variations in newborn's flora which reaches 1014 germs in the digestive system. In adults, the commensal flora or microbiota consists essentially of bacteria, in particular of 4 phyla, but also of yeasts and bacteriophage viruses. Physiologically, human develops tolerance against microbiota (Th3 lymphocytes, TGF-β, secretory IgA) and many interactions are essential for adaptation to our environment and preservation of intestinal homeostasis. Microbiota is involved in mucosal immune system (MALT) ontogeny in newborns. Then, throughout the life, MALT will be stimulated by microbiota to maintain tolerance, but also to develop protective immune responses against pathogens, with activation of Th17 lymphocytes and ILC (innate lymphoid cells). These inflammatory reactions are transient, and homeostasis is quickly restored. Otherwise, there is a breakdown of tolerance and development of pathological chronic inflammatory reactions.