In a study reported in this month's edition of Nature Medicine , the researchers show that immune system cells which fight bacteria can also attack normal cells carrying a specific molecule that closely resembles a bacterial protein. This occurs when the cells are stressed by exposure to irradiation, environmental toxins or the body's stress chemicals. The study also offers a starting place for scientists to investigate environmental or genetic triggers to autoimmune diseases. The team focused on infections by Salmonella, bacteria well known for food poisoning but also long thought to trigger arthritis in some people. But a smaller, significant number of those patients get a severe, debilitating type of arthritis that's long-lasting.
Cells invaded by bacteria normally give clear signals that they're infected.
This molecule helps proteins keep their shape. When researchers artificially coaxed mouse body cells to display the Salmonella flag, the mouse CTLs would readily attack them. But CTLs also went into attack mode if the cells displayed a piece of the mouse's own housekeeping molecule or the identical human version. That's a huge immune response. Based on the similarity of the set-up in humans, he adds, the response is likely the same.