Bacteria in the gut have been implicated in autoimmune diseases, like lupus, that don’t primarily affect the gastrointestinal system. But how those bacteria affect the human immune system remains unclear. In a new study, Yale researchers show how a gut bacterium called Enterococcus gallinarum can travel outside of the gastrointestinal system and trigger an autoimmune response. The lymph nodes and spleen are what are known as secondary lymphoid organs, which are part of the immune system and help launch immune responses. “Maybe in the future we wouldn’t just target the immune system when treating autoimmune diseases,” said Kriegel.