Autoimmune disease in children could be caused by gut bacteria that inhibit immune development.

Surface lipopolysaccharide (LPS) is made by microbes such as Escherichia coli and helps immune cells to mature. Ramnik Xavier of Harvard Medical School in Boston, Massachusetts, and his team studied the gut microbiomes and clinical history of more than 200 children in various countries from birth until age 3. Finnish children, who had higher rates of autoimmune disease than those from Russia, also had higher levels of Bacteroides strains than of E. coli, whereas Russian children had more E. coli. In cultured human white blood cells, LPS produced by Bacteroides dorei inhibited the stimulation that is needed to promote immune-system development.

Certain immune-stimulating LPS types might be needed in early life to 'educate' the immune system to more accurately recognize foreign molecules.

Cell (2016)