Paradoxically, while the detection systems are different, the actual immune defenses the body employs to clear the system of viral or bacterial infection are much the same. As are the symptoms--to you or me, fighting off bacteria or viruses can produce the same fatigue, inflammation, or hacking cough.
Now a team of researchers at The Scripps Research Institute (TSRI) has published a paper appearing in an upcoming issue of the journal Nature that explains how pathogens as different as viruses and bacteria can have such a common bottom line.
"The proximal reason [for these similar symptoms] is a single protein," says TSRI Professor Bruce Beutler, M.D., who led the research.
This protein, called Trif, associates with different "receptors" that detect a virus or a bacterium on the surfaces of human cells. Trif is a signal transducer--it helps turn these positive detections into immune reactions. Significantly, Trif is the topmost protein shared by the pathway that detects gram-negative bacteria and the pathway that detects most viruses. It is like a waiter who brings orders from two different customers into the same kitchen.
This is the first time that anyone has identified a protein that directly responds to the signals the innate immune system sends when it recognizes both bacteria and viruses.
In addition, Trif could be a potential target for intervening in diseases in which the innate immune system plays a role, such as sepsis. Sepsis basically results from a runaway cascade of inflammation in response to a bacterial infection, and Trif is involved very early in this cascade. If drugs might be designed that could modulate the function of Trif, they might help to improve the prognosis for sepsis.