SP0012 THE HYGIENE HYPOTHESIS IN AUTOIMMUNITY

Abstract

Background and Aims: The frequency of autoimmune diseases has increased significantly in recent decades in developed countries. The hygiene hypothesis provides a possible explanation for this increase. The hypothesis is based on the observation of a concomitant decrease in the frequency of infectious diseases and an increase in the frequency of autoimmune diseases. It is also based on the geographical disparity in the frequency of autoimmune diseases, much more frequent in the north than in the south of the northern hemisphere, a disparity that is not explained by genetics. Method: The disease frequency which is very low in southern countries increases from the first generation among subjects migrating northward. The causal relationship between the decline in infections and the increase in autoimmune diseases remains to be proven. Most of the evidence is based on spontaneous experimental models of autoimmune diseases that show the higher frequency of these diseases in a clean sanitary environment and their prevention through the administration of various bacteria, viruses or parasites. Results: The underlying mechanisms are beginning to be revealed. An important place is given to pathogens and more particularly to their TLR ligands. Some arguments suggest that commensal bacteria in the intestinal microbiota also play a role. At the cellular level, the stimulation of certain regulatory cells and more particularly those producing TGF beta is well documented. Conclusion: These considerations are important for understanding the epidemiology and pathophysiology of autoimmune diseases but can also provide new guidance on their treatment and especially their prevention. The problem is, however, complicated by the fact that the theory applies to varying degrees depending on the disease, for instance more in systemic lupus erythematosus than rheumatoid arthritis. Disclosure of Interests: None declared