Scientists have discovered that at the same time the immune system is vigorously attacking invading viruses or bacteria, it is unexpectedly reducing its production of a particular type of factor that directs the movement of immune cells. The new finding, which could help explain the transient immune suppression often seen during acute infections, shows that the immune system is even more complex than previously believed.

A natural mechanism pirated by tumors and HIV to evade the immune response is opening the door to better treatment for these conditions, researchers say.